a unary operator, but merely separates the arguments of a list
operator. A unary operator generally provides scalar context to its
argument, while a list operator may provide either scalar or list
-contexts for its arguments. If it does both, scalar arguments
+contexts for its arguments. If it does both, scalar arguments
come first and list argument follow, and there can only ever
-be one such list argument. For instance, splice() has three scalar
-arguments followed by a list, whereas gethostbyname() has four scalar
-arguments.
+be one such list argument. For instance,
+L<C<splice>|/splice ARRAY,OFFSET,LENGTH,LIST> has three scalar arguments
+followed by a list, whereas L<C<gethostbyname>|/gethostbyname NAME> has
+four scalar arguments.
In the syntax descriptions that follow, list operators that expect a
list (and provide list context for elements of the list) are shown
Any function in the list below may be used either with or without
parentheses around its arguments. (The syntax descriptions omit the
-parentheses.) If you use parentheses, the simple but occasionally
+parentheses.) If you use parentheses, the simple but occasionally
surprising rule is this: It I<looks> like a function, therefore it I<is> a
function, and precedence doesn't matter. Otherwise it's a list
operator or unary operator, and precedence does matter. Whitespace
print +(1+2)+4; # Prints 7.
print ((1+2)+4); # Prints 7.
-If you run Perl with the B<-w> switch it can warn you about this. For
-example, the third line above produces:
+If you run Perl with the L<C<use warnings>|warnings> pragma, it can warn
+you about this. For example, the third line above produces:
print (...) interpreted as function at - line 1.
Useless use of integer addition in void context at - line 1.
A few functions take no arguments at all, and therefore work as neither
-unary nor list operators. These include such functions as C<time>
-and C<endpwent>. For example, C<time+86_400> always means
-C<time() + 86_400>.
+unary nor list operators. These include such functions as
+L<C<time>|/time> and L<C<endpwent>|/endpwent>. For example,
+C<time+86_400> always means C<time() + 86_400>.
For functions that can be used in either a scalar or list context,
nonabortive failure is generally indicated in scalar context by
first glance appear to be a list in scalar context. You can't get a list
like C<(1,2,3)> into being in scalar context, because the compiler knows
the context at compile time. It would generate the scalar comma operator
-there, not the list construction version of the comma. That means it
+there, not the list concatenation version of the comma. That means it
was never a list to start with.
-In general, functions in Perl that serve as wrappers for system calls ("syscalls")
-of the same name (like chown(2), fork(2), closedir(2), etc.) return
-true when they succeed and C<undef> otherwise, as is usually mentioned
-in the descriptions below. This is different from the C interfaces,
-which return C<-1> on failure. Exceptions to this rule include C<wait>,
-C<waitpid>, and C<syscall>. System calls also set the special C<$!>
-variable on failure. Other functions do not, except accidentally.
+In general, functions in Perl that serve as wrappers for system calls
+("syscalls") of the same name (like L<chown(2)>, L<fork(2)>,
+L<closedir(2)>, etc.) return true when they succeed and
+L<C<undef>|/undef EXPR> otherwise, as is usually mentioned in the
+descriptions below. This is different from the C interfaces, which
+return C<-1> on failure. Exceptions to this rule include
+L<C<wait>|/wait>, L<C<waitpid>|/waitpid PID,FLAGS>, and
+L<C<syscall>|/syscall NUMBER, LIST>. System calls also set the special
+L<C<$!>|perlvar/$!> variable on failure. Other functions do not, except
+accidentally.
Extension modules can also hook into the Perl parser to define new
kinds of keyword-headed expression. These may look like functions, but
=for Pod::Functions =String
-C<chomp>, C<chop>, C<chr>, C<crypt>, C<fc>, C<hex>, C<index>, C<lc>,
-C<lcfirst>, C<length>, C<oct>, C<ord>, C<pack>, C<q//>, C<qq//>, C<reverse>,
-C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///>
-
-C<fc> is available only if the C<"fc"> feature is enabled or if it is
-prefixed with C<CORE::>. The C<"fc"> feature is enabled automatically
+L<C<chomp>|/chomp VARIABLE>, L<C<chop>|/chop VARIABLE>,
+L<C<chr>|/chr NUMBER>, L<C<crypt>|/crypt PLAINTEXT,SALT>,
+L<C<fc>|/fc EXPR>, L<C<hex>|/hex EXPR>,
+L<C<index>|/index STR,SUBSTR,POSITION>, L<C<lc>|/lc EXPR>,
+L<C<lcfirst>|/lcfirst EXPR>, L<C<length>|/length EXPR>,
+L<C<oct>|/oct EXPR>, L<C<ord>|/ord EXPR>,
+L<C<pack>|/pack TEMPLATE,LIST>,
+L<C<qE<sol>E<sol>>|/qE<sol>STRINGE<sol>>,
+L<C<qqE<sol>E<sol>>|/qqE<sol>STRINGE<sol>>, L<C<reverse>|/reverse LIST>,
+L<C<rindex>|/rindex STR,SUBSTR,POSITION>,
+L<C<sprintf>|/sprintf FORMAT, LIST>,
+L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT>,
+L<C<trE<sol>E<sol>E<sol>>|/trE<sol>E<sol>E<sol>>, L<C<uc>|/uc EXPR>,
+L<C<ucfirst>|/ucfirst EXPR>,
+L<C<yE<sol>E<sol>E<sol>>|/yE<sol>E<sol>E<sol>>
+
+L<C<fc>|/fc EXPR> is available only if the
+L<C<"fc"> feature|feature/The 'fc' feature> is enabled or if it is
+prefixed with C<CORE::>. The
+L<C<"fc"> feature|feature/The 'fc' feature> is enabled automatically
with a C<use v5.16> (or higher) declaration in the current scope.
-
=item Regular expressions and pattern matching
X<regular expression> X<regex> X<regexp>
=for Pod::Functions =Regexp
-C<m//>, C<pos>, C<qr//>, C<quotemeta>, C<s///>, C<split>, C<study>
+L<C<mE<sol>E<sol>>|/mE<sol>E<sol>>, L<C<pos>|/pos SCALAR>,
+L<C<qrE<sol>E<sol>>|/qrE<sol>STRINGE<sol>>,
+L<C<quotemeta>|/quotemeta EXPR>,
+L<C<sE<sol>E<sol>E<sol>>|/sE<sol>E<sol>E<sol>>,
+L<C<split>|/split E<sol>PATTERNE<sol>,EXPR,LIMIT>,
+L<C<study>|/study SCALAR>
=item Numeric functions
X<numeric> X<number> X<trigonometric> X<trigonometry>
=for Pod::Functions =Math
-C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>,
-C<sin>, C<sqrt>, C<srand>
+L<C<abs>|/abs VALUE>, L<C<atan2>|/atan2 Y,X>, L<C<cos>|/cos EXPR>,
+L<C<exp>|/exp EXPR>, L<C<hex>|/hex EXPR>, L<C<int>|/int EXPR>,
+L<C<log>|/log EXPR>, L<C<oct>|/oct EXPR>, L<C<rand>|/rand EXPR>,
+L<C<sin>|/sin EXPR>, L<C<sqrt>|/sqrt EXPR>, L<C<srand>|/srand EXPR>
=item Functions for real @ARRAYs
X<array>
=for Pod::Functions =ARRAY
-C<each>, C<keys>, C<pop>, C<push>, C<shift>, C<splice>, C<unshift>, C<values>
+L<C<each>|/each HASH>, L<C<keys>|/keys HASH>, L<C<pop>|/pop ARRAY>,
+L<C<push>|/push ARRAY,LIST>, L<C<shift>|/shift ARRAY>,
+L<C<splice>|/splice ARRAY,OFFSET,LENGTH,LIST>,
+L<C<unshift>|/unshift ARRAY,LIST>, L<C<values>|/values HASH>
=item Functions for list data
X<list>
=for Pod::Functions =LIST
-C<grep>, C<join>, C<map>, C<qw//>, C<reverse>, C<sort>, C<unpack>
+L<C<grep>|/grep BLOCK LIST>, L<C<join>|/join EXPR,LIST>,
+L<C<map>|/map BLOCK LIST>, L<C<qwE<sol>E<sol>>|/qwE<sol>STRINGE<sol>>,
+L<C<reverse>|/reverse LIST>, L<C<sort>|/sort SUBNAME LIST>,
+L<C<unpack>|/unpack TEMPLATE,EXPR>
=item Functions for real %HASHes
X<hash>
=for Pod::Functions =HASH
-C<delete>, C<each>, C<exists>, C<keys>, C<values>
+L<C<delete>|/delete EXPR>, L<C<each>|/each HASH>,
+L<C<exists>|/exists EXPR>, L<C<keys>|/keys HASH>,
+L<C<values>|/values HASH>
=item Input and output functions
X<I/O> X<input> X<output> X<dbm>
=for Pod::Functions =I/O
-C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>,
-C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>,
-C<readdir>, C<readline> C<rewinddir>, C<say>, C<seek>, C<seekdir>, C<select>,
-C<syscall>, C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>,
-C<truncate>, C<warn>, C<write>
-
-C<say> is available only if the C<"say"> feature is enabled or if it is
-prefixed with C<CORE::>. The C<"say"> feature is enabled automatically
+L<C<binmode>|/binmode FILEHANDLE, LAYER>, L<C<close>|/close FILEHANDLE>,
+L<C<closedir>|/closedir DIRHANDLE>, L<C<dbmclose>|/dbmclose HASH>,
+L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK>, L<C<die>|/die LIST>,
+L<C<eof>|/eof FILEHANDLE>, L<C<fileno>|/fileno FILEHANDLE>,
+L<C<flock>|/flock FILEHANDLE,OPERATION>, L<C<format>|/format>,
+L<C<getc>|/getc FILEHANDLE>, L<C<print>|/print FILEHANDLE LIST>,
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST>,
+L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<readdir>|/readdir DIRHANDLE>, L<C<readline>|/readline EXPR>
+L<C<rewinddir>|/rewinddir DIRHANDLE>, L<C<say>|/say FILEHANDLE LIST>,
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<seekdir>|/seekdir DIRHANDLE,POS>,
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT>,
+L<C<syscall>|/syscall NUMBER, LIST>,
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE>,
+L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<tell>|/tell FILEHANDLE>, L<C<telldir>|/telldir DIRHANDLE>,
+L<C<truncate>|/truncate FILEHANDLE,LENGTH>, L<C<warn>|/warn LIST>,
+L<C<write>|/write FILEHANDLE>
+
+L<C<say>|/say FILEHANDLE LIST> is available only if the
+L<C<"say"> feature|feature/The 'say' feature> is enabled or if it is
+prefixed with C<CORE::>. The
+L<C<"say"> feature|feature/The 'say' feature> is enabled automatically
with a C<use v5.10> (or higher) declaration in the current scope.
=item Functions for fixed-length data or records
=for Pod::Functions =Binary
-C<pack>, C<read>, C<syscall>, C<sysread>, C<sysseek>, C<syswrite>, C<unpack>,
-C<vec>
+L<C<pack>|/pack TEMPLATE,LIST>,
+L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<syscall>|/syscall NUMBER, LIST>,
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE>,
+L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<unpack>|/unpack TEMPLATE,EXPR>, L<C<vec>|/vec EXPR,OFFSET,BITS>
=item Functions for filehandles, files, or directories
X<file> X<filehandle> X<directory> X<pipe> X<link> X<symlink>
=for Pod::Functions =File
-C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>,
-C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>,
-C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<sysopen>,
-C<umask>, C<unlink>, C<utime>
+L<C<-I<X>>|/-X FILEHANDLE>, L<C<chdir>|/chdir EXPR>,
+L<C<chmod>|/chmod LIST>, L<C<chown>|/chown LIST>,
+L<C<chroot>|/chroot FILENAME>,
+L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR>, L<C<glob>|/glob EXPR>,
+L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>,
+L<C<link>|/link OLDFILE,NEWFILE>, L<C<lstat>|/lstat FILEHANDLE>,
+L<C<mkdir>|/mkdir FILENAME,MASK>, L<C<open>|/open FILEHANDLE,EXPR>,
+L<C<opendir>|/opendir DIRHANDLE,EXPR>, L<C<readlink>|/readlink EXPR>,
+L<C<rename>|/rename OLDNAME,NEWNAME>, L<C<rmdir>|/rmdir FILENAME>,
+L<C<select>|/select FILEHANDLE>, L<C<stat>|/stat FILEHANDLE>,
+L<C<symlink>|/symlink OLDFILE,NEWFILE>,
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE>,
+L<C<umask>|/umask EXPR>, L<C<unlink>|/unlink LIST>,
+L<C<utime>|/utime LIST>
=item Keywords related to the control flow of your Perl program
X<control flow>
=for Pod::Functions =Flow
-C<break>, C<caller>, C<continue>, C<die>, C<do>,
-C<dump>, C<eval>, C<evalbytes> C<exit>,
-C<__FILE__>, C<goto>, C<last>, C<__LINE__>, C<next>, C<__PACKAGE__>,
-C<redo>, C<return>, C<sub>, C<__SUB__>, C<wantarray>
-
-C<break> is available only if you enable the experimental C<"switch">
-feature or use the C<CORE::> prefix. The C<"switch"> feature also enables
-the C<default>, C<given> and C<when> statements, which are documented in
-L<perlsyn/"Switch Statements">. The C<"switch"> feature is enabled
+L<C<break>|/break>, L<C<caller>|/caller EXPR>,
+L<C<continue>|/continue BLOCK>, L<C<die>|/die LIST>, L<C<do>|/do BLOCK>,
+L<C<dump>|/dump LABEL>, L<C<eval>|/eval EXPR>,
+L<C<evalbytes>|/evalbytes EXPR> L<C<exit>|/exit EXPR>,
+L<C<__FILE__>|/__FILE__>, L<C<goto>|/goto LABEL>,
+L<C<last>|/last LABEL>, L<C<__LINE__>|/__LINE__>,
+L<C<next>|/next LABEL>, L<C<__PACKAGE__>|/__PACKAGE__>,
+L<C<redo>|/redo LABEL>, L<C<return>|/return EXPR>,
+L<C<sub>|/sub NAME BLOCK>, L<C<__SUB__>|/__SUB__>,
+L<C<wantarray>|/wantarray>
+
+L<C<break>|/break> is available only if you enable the experimental
+L<C<"switch"> feature|feature/The 'switch' feature> or use the C<CORE::>
+prefix. The L<C<"switch"> feature|feature/The 'switch' feature> also
+enables the C<default>, C<given> and C<when> statements, which are
+documented in L<perlsyn/"Switch Statements">.
+The L<C<"switch"> feature|feature/The 'switch' feature> is enabled
automatically with a C<use v5.10> (or higher) declaration in the current
-scope. In Perl v5.14 and earlier, C<continue> required the C<"switch">
-feature, like the other keywords.
-
-C<evalbytes> is only available with the C<"evalbytes"> feature (see
-L<feature>) or if prefixed with C<CORE::>. C<__SUB__> is only available
-with the C<"current_sub"> feature or if prefixed with C<CORE::>. Both
-the C<"evalbytes"> and C<"current_sub"> features are enabled automatically
-with a C<use v5.16> (or higher) declaration in the current scope.
+scope. In Perl v5.14 and earlier, L<C<continue>|/continue BLOCK>
+required the L<C<"switch"> feature|feature/The 'switch' feature>, like
+the other keywords.
+
+L<C<evalbytes>|/evalbytes EXPR> is only available with the
+L<C<"evalbytes"> feature|feature/The 'unicode_eval' and 'evalbytes' features>
+(see L<feature>) or if prefixed with C<CORE::>. L<C<__SUB__>|/__SUB__>
+is only available with the
+L<C<"current_sub"> feature|feature/The 'current_sub' feature> or if
+prefixed with C<CORE::>. Both the
+L<C<"evalbytes">|feature/The 'unicode_eval' and 'evalbytes' features>
+and L<C<"current_sub">|feature/The 'current_sub' feature> features are
+enabled automatically with a C<use v5.16> (or higher) declaration in the
+current scope.
=item Keywords related to scoping
=for Pod::Functions =Namespace
-C<caller>, C<import>, C<local>, C<my>, C<our>, C<package>, C<state>, C<use>
+L<C<caller>|/caller EXPR>, L<C<import>|/import LIST>,
+L<C<local>|/local EXPR>, L<C<my>|/my VARLIST>, L<C<our>|/our VARLIST>,
+L<C<package>|/package NAMESPACE>, L<C<state>|/state VARLIST>,
+L<C<use>|/use Module VERSION LIST>
-C<state> is available only if the C<"state"> feature is enabled or if it is
-prefixed with C<CORE::>. The C<"state"> feature is enabled automatically
-with a C<use v5.10> (or higher) declaration in the current scope.
+L<C<state>|/state VARLIST> is available only if the
+L<C<"state"> feature|feature/The 'state' feature> is enabled or if it is
+prefixed with C<CORE::>. The
+L<C<"state"> feature|feature/The 'state' feature> is enabled
+automatically with a C<use v5.10> (or higher) declaration in the current
+scope.
=item Miscellaneous functions
=for Pod::Functions =Misc
-C<defined>, C<formline>, C<lock>, C<prototype>, C<reset>, C<scalar>, C<undef>
+L<C<defined>|/defined EXPR>, L<C<formline>|/formline PICTURE,LIST>,
+L<C<lock>|/lock THING>, L<C<prototype>|/prototype FUNCTION>,
+L<C<reset>|/reset EXPR>, L<C<scalar>|/scalar EXPR>,
+L<C<undef>|/undef EXPR>
=item Functions for processes and process groups
X<process> X<pid> X<process id>
=for Pod::Functions =Process
-C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>,
-C<pipe>, C<qx//>, C<readpipe>, C<setpgrp>,
-C<setpriority>, C<sleep>, C<system>,
-C<times>, C<wait>, C<waitpid>
+L<C<alarm>|/alarm SECONDS>, L<C<exec>|/exec LIST>, L<C<fork>|/fork>,
+L<C<getpgrp>|/getpgrp PID>, L<C<getppid>|/getppid>,
+L<C<getpriority>|/getpriority WHICH,WHO>, L<C<kill>|/kill SIGNAL, LIST>,
+L<C<pipe>|/pipe READHANDLE,WRITEHANDLE>,
+L<C<qxE<sol>E<sol>>|/qxE<sol>STRINGE<sol>>,
+L<C<readpipe>|/readpipe EXPR>, L<C<setpgrp>|/setpgrp PID,PGRP>,
+L<C<setpriority>|/setpriority WHICH,WHO,PRIORITY>,
+L<C<sleep>|/sleep EXPR>, L<C<system>|/system LIST>, L<C<times>|/times>,
+L<C<wait>|/wait>, L<C<waitpid>|/waitpid PID,FLAGS>
=item Keywords related to Perl modules
X<module>
=for Pod::Functions =Modules
-C<do>, C<import>, C<no>, C<package>, C<require>, C<use>
+L<C<do>|/do EXPR>, L<C<import>|/import LIST>,
+L<C<no>|/no MODULE VERSION LIST>, L<C<package>|/package NAMESPACE>,
+L<C<require>|/require VERSION>, L<C<use>|/use Module VERSION LIST>
=item Keywords related to classes and object-orientation
X<object> X<class> X<package>
=for Pod::Functions =Objects
-C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>,
-C<untie>, C<use>
+L<C<bless>|/bless REF,CLASSNAME>, L<C<dbmclose>|/dbmclose HASH>,
+L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK>,
+L<C<package>|/package NAMESPACE>, L<C<ref>|/ref EXPR>,
+L<C<tie>|/tie VARIABLE,CLASSNAME,LIST>, L<C<tied>|/tied VARIABLE>,
+L<C<untie>|/untie VARIABLE>, L<C<use>|/use Module VERSION LIST>
=item Low-level socket functions
X<socket> X<sock>
=for Pod::Functions =Socket
-C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>,
-C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>,
-C<socket>, C<socketpair>
+L<C<accept>|/accept NEWSOCKET,GENERICSOCKET>,
+L<C<bind>|/bind SOCKET,NAME>, L<C<connect>|/connect SOCKET,NAME>,
+L<C<getpeername>|/getpeername SOCKET>,
+L<C<getsockname>|/getsockname SOCKET>,
+L<C<getsockopt>|/getsockopt SOCKET,LEVEL,OPTNAME>,
+L<C<listen>|/listen SOCKET,QUEUESIZE>,
+L<C<recv>|/recv SOCKET,SCALAR,LENGTH,FLAGS>,
+L<C<send>|/send SOCKET,MSG,FLAGS,TO>,
+L<C<setsockopt>|/setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL>,
+L<C<shutdown>|/shutdown SOCKET,HOW>,
+L<C<socket>|/socket SOCKET,DOMAIN,TYPE,PROTOCOL>,
+L<C<socketpair>|/socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL>
=item System V interprocess communication functions
X<IPC> X<System V> X<semaphore> X<shared memory> X<memory> X<message>
=for Pod::Functions =SysV
-C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>,
-C<shmctl>, C<shmget>, C<shmread>, C<shmwrite>
+L<C<msgctl>|/msgctl ID,CMD,ARG>, L<C<msgget>|/msgget KEY,FLAGS>,
+L<C<msgrcv>|/msgrcv ID,VAR,SIZE,TYPE,FLAGS>,
+L<C<msgsnd>|/msgsnd ID,MSG,FLAGS>,
+L<C<semctl>|/semctl ID,SEMNUM,CMD,ARG>,
+L<C<semget>|/semget KEY,NSEMS,FLAGS>, L<C<semop>|/semop KEY,OPSTRING>,
+L<C<shmctl>|/shmctl ID,CMD,ARG>, L<C<shmget>|/shmget KEY,SIZE,FLAGS>,
+L<C<shmread>|/shmread ID,VAR,POS,SIZE>,
+L<C<shmwrite>|/shmwrite ID,STRING,POS,SIZE>
=item Fetching user and group info
X<user> X<group> X<password> X<uid> X<gid> X<passwd> X</etc/passwd>
=for Pod::Functions =User
-C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>,
-C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>,
-C<getpwuid>, C<setgrent>, C<setpwent>
+L<C<endgrent>|/endgrent>, L<C<endhostent>|/endhostent>,
+L<C<endnetent>|/endnetent>, L<C<endpwent>|/endpwent>,
+L<C<getgrent>|/getgrent>, L<C<getgrgid>|/getgrgid GID>,
+L<C<getgrnam>|/getgrnam NAME>, L<C<getlogin>|/getlogin>,
+L<C<getpwent>|/getpwent>, L<C<getpwnam>|/getpwnam NAME>,
+L<C<getpwuid>|/getpwuid UID>, L<C<setgrent>|/setgrent>,
+L<C<setpwent>|/setpwent>
=item Fetching network info
X<network> X<protocol> X<host> X<hostname> X<IP> X<address> X<service>
=for Pod::Functions =Network
-C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>,
-C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
-C<getprotobyname>, C<getprotobynumber>, C<getprotoent>,
-C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>,
-C<setnetent>, C<setprotoent>, C<setservent>
+L<C<endprotoent>|/endprotoent>, L<C<endservent>|/endservent>,
+L<C<gethostbyaddr>|/gethostbyaddr ADDR,ADDRTYPE>,
+L<C<gethostbyname>|/gethostbyname NAME>, L<C<gethostent>|/gethostent>,
+L<C<getnetbyaddr>|/getnetbyaddr ADDR,ADDRTYPE>,
+L<C<getnetbyname>|/getnetbyname NAME>, L<C<getnetent>|/getnetent>,
+L<C<getprotobyname>|/getprotobyname NAME>,
+L<C<getprotobynumber>|/getprotobynumber NUMBER>,
+L<C<getprotoent>|/getprotoent>,
+L<C<getservbyname>|/getservbyname NAME,PROTO>,
+L<C<getservbyport>|/getservbyport PORT,PROTO>,
+L<C<getservent>|/getservent>, L<C<sethostent>|/sethostent STAYOPEN>,
+L<C<setnetent>|/setnetent STAYOPEN>,
+L<C<setprotoent>|/setprotoent STAYOPEN>,
+L<C<setservent>|/setservent STAYOPEN>
=item Time-related functions
X<time> X<date>
=for Pod::Functions =Time
-C<gmtime>, C<localtime>, C<time>, C<times>
+L<C<gmtime>|/gmtime EXPR>, L<C<localtime>|/localtime EXPR>,
+L<C<time>|/time>, L<C<times>|/times>
=item Non-function keywords
functionality may differ slightly. The Perl functions affected
by this are:
-C<-X>, C<binmode>, C<chmod>, C<chown>, C<chroot>, C<crypt>,
-C<dbmclose>, C<dbmopen>, C<dump>, C<endgrent>, C<endhostent>,
-C<endnetent>, C<endprotoent>, C<endpwent>, C<endservent>, C<exec>,
-C<fcntl>, C<flock>, C<fork>, C<getgrent>, C<getgrgid>, C<gethostbyname>,
-C<gethostent>, C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
-C<getppid>, C<getpgrp>, C<getpriority>, C<getprotobynumber>,
-C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>,
-C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>,
-C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>,
-C<msgsnd>, C<open>, C<pipe>, C<readlink>, C<rename>, C<select>, C<semctl>,
-C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>,
-C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>,
-C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>,
-C<shmwrite>, C<socket>, C<socketpair>,
-C<stat>, C<symlink>, C<syscall>, C<sysopen>, C<system>,
-C<times>, C<truncate>, C<umask>, C<unlink>,
-C<utime>, C<wait>, C<waitpid>
+L<C<-I<X>>|/-X FILEHANDLE>, L<C<binmode>|/binmode FILEHANDLE, LAYER>,
+L<C<chmod>|/chmod LIST>, L<C<chown>|/chown LIST>,
+L<C<chroot>|/chroot FILENAME>, L<C<crypt>|/crypt PLAINTEXT,SALT>,
+L<C<dbmclose>|/dbmclose HASH>, L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK>,
+L<C<dump>|/dump LABEL>, L<C<endgrent>|/endgrent>,
+L<C<endhostent>|/endhostent>, L<C<endnetent>|/endnetent>,
+L<C<endprotoent>|/endprotoent>, L<C<endpwent>|/endpwent>,
+L<C<endservent>|/endservent>, L<C<exec>|/exec LIST>,
+L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR>,
+L<C<flock>|/flock FILEHANDLE,OPERATION>, L<C<fork>|/fork>,
+L<C<getgrent>|/getgrent>, L<C<getgrgid>|/getgrgid GID>,
+L<C<gethostbyname>|/gethostbyname NAME>, L<C<gethostent>|/gethostent>,
+L<C<getlogin>|/getlogin>,
+L<C<getnetbyaddr>|/getnetbyaddr ADDR,ADDRTYPE>,
+L<C<getnetbyname>|/getnetbyname NAME>, L<C<getnetent>|/getnetent>,
+L<C<getppid>|/getppid>, L<C<getpgrp>|/getpgrp PID>,
+L<C<getpriority>|/getpriority WHICH,WHO>,
+L<C<getprotobynumber>|/getprotobynumber NUMBER>,
+L<C<getprotoent>|/getprotoent>, L<C<getpwent>|/getpwent>,
+L<C<getpwnam>|/getpwnam NAME>, L<C<getpwuid>|/getpwuid UID>,
+L<C<getservbyport>|/getservbyport PORT,PROTO>,
+L<C<getservent>|/getservent>,
+L<C<getsockopt>|/getsockopt SOCKET,LEVEL,OPTNAME>,
+L<C<glob>|/glob EXPR>, L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>,
+L<C<kill>|/kill SIGNAL, LIST>, L<C<link>|/link OLDFILE,NEWFILE>,
+L<C<lstat>|/lstat FILEHANDLE>, L<C<msgctl>|/msgctl ID,CMD,ARG>,
+L<C<msgget>|/msgget KEY,FLAGS>,
+L<C<msgrcv>|/msgrcv ID,VAR,SIZE,TYPE,FLAGS>,
+L<C<msgsnd>|/msgsnd ID,MSG,FLAGS>, L<C<open>|/open FILEHANDLE,EXPR>,
+L<C<pipe>|/pipe READHANDLE,WRITEHANDLE>, L<C<readlink>|/readlink EXPR>,
+L<C<rename>|/rename OLDNAME,NEWNAME>,
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT>,
+L<C<semctl>|/semctl ID,SEMNUM,CMD,ARG>,
+L<C<semget>|/semget KEY,NSEMS,FLAGS>, L<C<semop>|/semop KEY,OPSTRING>,
+L<C<setgrent>|/setgrent>, L<C<sethostent>|/sethostent STAYOPEN>,
+L<C<setnetent>|/setnetent STAYOPEN>, L<C<setpgrp>|/setpgrp PID,PGRP>,
+L<C<setpriority>|/setpriority WHICH,WHO,PRIORITY>,
+L<C<setprotoent>|/setprotoent STAYOPEN>, L<C<setpwent>|/setpwent>,
+L<C<setservent>|/setservent STAYOPEN>,
+L<C<setsockopt>|/setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL>,
+L<C<shmctl>|/shmctl ID,CMD,ARG>, L<C<shmget>|/shmget KEY,SIZE,FLAGS>,
+L<C<shmread>|/shmread ID,VAR,POS,SIZE>,
+L<C<shmwrite>|/shmwrite ID,STRING,POS,SIZE>,
+L<C<socket>|/socket SOCKET,DOMAIN,TYPE,PROTOCOL>,
+L<C<socketpair>|/socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL>,
+L<C<stat>|/stat FILEHANDLE>, L<C<symlink>|/symlink OLDFILE,NEWFILE>,
+L<C<syscall>|/syscall NUMBER, LIST>,
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE>,
+L<C<system>|/system LIST>, L<C<times>|/times>,
+L<C<truncate>|/truncate FILEHANDLE,LENGTH>, L<C<umask>|/umask EXPR>,
+L<C<unlink>|/unlink LIST>, L<C<utime>|/utime LIST>, L<C<wait>|/wait>,
+L<C<waitpid>|/waitpid PID,FLAGS>
For more information about the portability of these functions, see
L<perlport> and other available platform-specific documentation.
=head2 Alphabetical Listing of Perl Functions
-=over
+=over
=item -X FILEHANDLE
X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p>
=for Pod::Functions a file test (-r, -x, etc)
A file test, where X is one of the letters listed below. This unary
-operator takes one argument, either a filename, a filehandle, or a dirhandle,
+operator takes one argument, either a filename, a filehandle, or a dirhandle,
and tests the associated file to see if something is true about it. If the
-argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN.
-Unless otherwise documented, it returns C<1> for true and C<''> for false.
-If the file doesn't exist or can't be examined, it returns C<undef> and
-sets C<$!> (errno). Despite the funny names, precedence is the same as any
-other named unary operator. The operator may be any of:
+argument is omitted, tests L<C<$_>|perlvar/$_>, except for C<-t>, which
+tests STDIN. Unless otherwise documented, it returns C<1> for true and
+C<''> for false. If the file doesn't exist or can't be examined, it
+returns L<C<undef>|/undef EXPR> and sets L<C<$!>|perlvar/$!> (errno).
+Despite the funny names, precedence is the same as any other named unary
+operator. The operator may be any of:
-r File is readable by effective uid/gid.
-w File is writable by effective uid/gid.
Also note that, for the superuser on the local filesystems, the C<-r>,
C<-R>, C<-w>, and C<-W> tests always return 1, and C<-x> and C<-X> return 1
if any execute bit is set in the mode. Scripts run by the superuser
-may thus need to do a stat() to determine the actual mode of the file,
-or temporarily set their effective uid to something else.
-
-If you are using ACLs, there is a pragma called C<filetest> that may
-produce more accurate results than the bare stat() mode bits.
-When under C<use filetest 'access'> the above-mentioned filetests
-test whether the permission can(not) be granted using the
-access(2) family of system calls. Also note that the C<-x> and C<-X> may
+may thus need to do a L<C<stat>|/stat FILEHANDLE> to determine the
+actual mode of the file, or temporarily set their effective uid to
+something else.
+
+If you are using ACLs, there is a pragma called L<C<filetest>|filetest>
+that may produce more accurate results than the bare
+L<C<stat>|/stat FILEHANDLE> mode bits.
+When under C<use filetest 'access'>, the above-mentioned filetests
+test whether the permission can(not) be granted using the L<access(2)>
+family of system calls. Also note that the C<-x> and C<-X> tests may
under this pragma return true even if there are no execute permission
bits set (nor any extra execute permission ACLs). This strangeness is
due to the underlying system calls' definitions. Note also that, due to
the implementation of C<use filetest 'access'>, the C<_> special
filehandle won't cache the results of the file tests when this pragma is
-in effect. Read the documentation for the C<filetest> pragma for more
-information.
+in effect. Read the documentation for the L<C<filetest>|filetest>
+pragma for more information.
-The C<-T> and C<-B> switches work as follows. The first block or so of
+The C<-T> and C<-B> tests work as follows. The first block or so of
the file is examined to see if it is valid UTF-8 that includes non-ASCII
-characters. If, so it's a C<-T> file. Otherwise, that same portion of
+characters. If so, it's a C<-T> file. Otherwise, that same portion of
the file is examined for odd characters such as strange control codes or
characters with the high bit set. If more than a third of the
characters are strange, it's a C<-B> file; otherwise it's a C<-T> file.
read a file to do the C<-T> test, on most occasions you want to use a C<-f>
against the file first, as in C<next unless -f $file && -T $file>.
-If any of the file tests (or either the C<stat> or C<lstat> operator) is given
-the special filehandle consisting of a solitary underline, then the stat
-structure of the previous file test (or stat operator) is used, saving
-a system call. (This doesn't work with C<-t>, and you need to remember
-that lstat() and C<-l> leave values in the stat structure for the
-symbolic link, not the real file.) (Also, if the stat buffer was filled by
-an C<lstat> call, C<-T> and C<-B> will reset it with the results of C<stat _>).
+If any of the file tests (or either the L<C<stat>|/stat FILEHANDLE> or
+L<C<lstat>|/lstat FILEHANDLE> operator) is given the special filehandle
+consisting of a solitary underline, then the stat structure of the
+previous file test (or L<C<stat>|/stat FILEHANDLE> operator) is used,
+saving a system call. (This doesn't work with C<-t>, and you need to
+remember that L<C<lstat>|/lstat FILEHANDLE> and C<-l> leave values in
+the stat structure for the symbolic link, not the real file.) (Also, if
+the stat buffer was filled by an L<C<lstat>|/lstat FILEHANDLE> call,
+C<-T> and C<-B> will reset it with the results of C<stat _>).
Example:
print "Can do.\n" if -r $a || -w _ || -x _;
=for Pod::Functions absolute value function
Returns the absolute value of its argument.
-If VALUE is omitted, uses C<$_>.
+If VALUE is omitted, uses L<C<$_>|perlvar/$_>.
=item accept NEWSOCKET,GENERICSOCKET
X<accept>
=for Pod::Functions accept an incoming socket connect
-Accepts an incoming socket connect, just as accept(2)
+Accepts an incoming socket connect, just as L<accept(2)>
does. Returns the packed address if it succeeded, false otherwise.
See the example in L<perlipc/"Sockets: Client/Server Communication">.
On systems that support a close-on-exec flag on files, the flag will
be set for the newly opened file descriptor, as determined by the
-value of
$^F. See L<perlvar/$^F>.
+value of
L<C<$^F>|perlvar/$^F>. See L<perlvar/$^F>.
=item alarm SECONDS
X<alarm>
Arranges to have a SIGALRM delivered to this process after the
specified number of wallclock seconds has elapsed. If SECONDS is not
-specified, the value stored in C<$_> is used. (On some machines,
-unfortunately, the elapsed time may be up to one second less or more
-than you specified because of how seconds are counted, and process
-scheduling may delay the delivery of the signal even further.)
+specified, the value stored in L<C<$_>|perlvar/$_> is used. (On some
+machines, unfortunately, the elapsed time may be up to one second less
+or more than you specified because of how seconds are counted, and
+process scheduling may delay the delivery of the signal even further.)
Only one timer may be counting at once. Each call disables the
previous timer, and an argument of C<0> may be supplied to cancel the
previous timer without starting a new one. The returned value is the
amount of time remaining on the previous timer.
-For delays of finer granularity than one second, the Time::HiRes module
+For delays of finer granularity than one second, the L<Time::HiRes> module
(from CPAN, and starting from Perl 5.8 part of the standard
-distribution) provides ualarm(). You may also use Perl's four-argument
-version of select() leaving the first three arguments undefined, or you
-might be able to use the C<syscall> interface to access setitimer(2) if
-your system supports it. See L<perlfaq8> for details.
-
-It is usually a mistake to intermix C<alarm> and C<sleep> calls, because
-C<sleep> may be internally implemented on your system with C<alarm>.
-
-If you want to use C<alarm> to time out a system call you need to use an
-C<eval>/C<die> pair. You can't rely on the alarm causing the system call to
-fail with C<$!> set to C<EINTR> because Perl sets up signal handlers to
-restart system calls on some systems. Using C<eval>/C<die> always works,
-modulo the caveats given in L<perlipc/"Signals">.
+distribution) provides
+L<C<ualarm>|Time::HiRes/ualarm ( $useconds [, $interval_useconds ] )>.
+You may also use Perl's four-argument version of
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT> leaving the first three
+arguments undefined, or you might be able to use the
+L<C<syscall>|/syscall NUMBER, LIST> interface to access L<setitimer(2)>
+if your system supports it. See L<perlfaq8> for details.
+
+It is usually a mistake to intermix L<C<alarm>|/alarm SECONDS> and
+L<C<sleep>|/sleep EXPR> calls, because L<C<sleep>|/sleep EXPR> may be
+internally implemented on your system with L<C<alarm>|/alarm SECONDS>.
+
+If you want to use L<C<alarm>|/alarm SECONDS> to time out a system call
+you need to use an L<C<eval>|/eval EXPR>/L<C<die>|/die LIST> pair. You
+can't rely on the alarm causing the system call to fail with
+L<C<$!>|perlvar/$!> set to C<EINTR> because Perl sets up signal handlers
+to restart system calls on some systems. Using
+L<C<eval>|/eval EXPR>/L<C<die>|/die LIST> always works, modulo the
+caveats given in L<perlipc/"Signals">.
eval {
local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
alarm $timeout;
- $nread = sysread SOCKET, $buffer, $size;
+ my $nread = sysread $socket, $buffer, $size;
alarm 0;
};
if ($@) {
Returns the arctangent of Y/X in the range -PI to PI.
-For the tangent operation, you may use the C<Math::Trig::tan>
-function, or use the familiar relation:
+For the tangent operation, you may use the
+L<C<Math::Trig::tan>|Math::Trig/B<tan>> function, or use the familiar
+relation:
sub tan { sin($_[0]) / cos($_[0]) }
The return value for C<atan2(0,0)> is implementation-defined; consult
-your atan2(3) manpage for more information.
+your L<atan2(3)> manpage for more information.
Portability issues: L<perlport/atan2>.
=for Pod::Functions binds an address to a socket
-Binds a network address to a socket, just as bind(2)
+Binds a network address to a socket, just as L<bind(2)>
does. Returns true if it succeeded, false otherwise. NAME should be a
packed address of the appropriate type for the socket. See the examples in
L<perlipc/"Sockets: Client/Server Communication">.
mode on systems where the run-time libraries distinguish between
binary and text files. If FILEHANDLE is an expression, the value is
taken as the name of the filehandle. Returns true on success,
-otherwise it returns C<undef> and sets C<$!> (errno).
+otherwise it returns L<C<undef>|/undef EXPR> and sets
+L<C<$!>|perlvar/$!> (errno).
-On some systems (in general, DOS- and Windows-based systems) binmode()
-is necessary when you're not working with a text file. For the sake
-of portability it is a good idea always to use it when appropriate,
-and never to use it when it isn't appropriate. Also, people can
-set their I/O to be by default UTF8-encoded Unicode, not bytes.
+On some systems (in general, DOS- and Windows-based systems)
+L<C<binmode>|/binmode FILEHANDLE, LAYER> is necessary when you're not
+working with a text file. For the sake of portability it is a good idea
+always to use it when appropriate, and never to use it when it isn't
+appropriate. Also, people can set their I/O to be by default
+UTF8-encoded Unicode, not bytes.
-In other words: regardless of platform, use binmode() on binary data,
-like images, for example.
+In other words: regardless of platform, use
+L<C<binmode>|/binmode FILEHANDLE, LAYER> on binary data, like images,
+for example.
If LAYER is present it is a single string, but may contain multiple
directives. The directives alter the behaviour of the filehandle.
PERLIO environment variable.
The C<:bytes>, C<:crlf>, C<:utf8>, and any other directives of the
-form C<:...>, are called I/O I<layers>. The C<open> pragma can be used to
-establish default I/O layers. See L<open>.
+form C<:...>, are called I/O I<layers>. The L<open> pragma can be used to
+establish default I/O layers.
-I<The LAYER parameter of the binmode() function is described as "DISCIPLINE"
-in "Programming Perl, 3rd Edition". However, since the publishing of this
-book, by many known as "Camel III", the consensus of the naming of this
-functionality has moved from "discipline" to "layer". All documentation
-of this version of Perl therefore refers to "layers" rather than to
-"disciplines". Now back to the regularly scheduled documentation...>
+I<The LAYER parameter of the L<C<binmode>|/binmode FILEHANDLE, LAYER>
+function is described as "DISCIPLINE" in "Programming Perl, 3rd
+Edition". However, since the publishing of this book, by many known as
+"Camel III", the consensus of the naming of this functionality has moved
+from "discipline" to "layer". All documentation of this version of Perl
+therefore refers to "layers" rather than to "disciplines". Now back to
+the regularly scheduled documentation...>
To mark FILEHANDLE as UTF-8, use C<:utf8> or C<:encoding(UTF-8)>.
C<:utf8> just marks the data as UTF-8 without further checking,
while C<:encoding(UTF-8)> checks the data for actually being valid
UTF-8. More details can be found in L<PerlIO::encoding>.
-In general, binmode() should be called after open() but before any I/O
-is done on the filehandle. Calling binmode() normally flushes any
-pending buffered output data (and perhaps pending input data) on the
-handle. An exception to this is the C<:encoding> layer that
-changes the default character encoding of the handle; see L</open>.
+In general, L<C<binmode>|/binmode FILEHANDLE, LAYER> should be called
+after L<C<open>|/open FILEHANDLE,EXPR> but before any I/O is done on the
+filehandle. Calling L<C<binmode>|/binmode FILEHANDLE, LAYER> normally
+flushes any pending buffered output data (and perhaps pending input
+data) on the handle. An exception to this is the C<:encoding> layer
+that changes the default character encoding of the handle.
The C<:encoding> layer sometimes needs to be called in
-mid-stream, and it doesn't flush the stream. The C<:encoding>
+mid-stream, and it doesn't flush the stream. C<:encoding>
also implicitly pushes on top of itself the C<:utf8> layer because
internally Perl operates on UTF8-encoded Unicode characters.
flavors of Mac OS, and is LINE FEED on Unix and most VMS files). In other
systems like OS/2, DOS, and the various flavors of MS-Windows, your program
sees a C<\n> as a simple C<\cJ>, but what's stored in text files are the
-two characters C<\cM\cJ>. That means that if you don't use binmode() on
-these systems, C<\cM\cJ> sequences on disk will be converted to C<\n> on
-input, and any C<\n> in your program will be converted back to C<\cM\cJ> on
-output. This is what you want for text files, but it can be disastrous for
-binary files.
-
-Another consequence of using binmode() (on some systems) is that
-special end-of-file markers will be seen as part of the data stream.
-For systems from the Microsoft family this means that, if your binary
-data contain C<\cZ>, the I/O subsystem will regard it as the end of
-the file, unless you use binmode().
-
-binmode() is important not only for readline() and print() operations,
-but also when using read(), seek(), sysread(), syswrite() and tell()
-(see L<perlport> for more details). See the C<$/> and C<$\> variables
-in L<perlvar> for how to manually set your input and output
+two characters C<\cM\cJ>. That means that if you don't use
+L<C<binmode>|/binmode FILEHANDLE, LAYER> on these systems, C<\cM\cJ>
+sequences on disk will be converted to C<\n> on input, and any C<\n> in
+your program will be converted back to C<\cM\cJ> on output. This is
+what you want for text files, but it can be disastrous for binary files.
+
+Another consequence of using L<C<binmode>|/binmode FILEHANDLE, LAYER>
+(on some systems) is that special end-of-file markers will be seen as
+part of the data stream. For systems from the Microsoft family this
+means that, if your binary data contain C<\cZ>, the I/O subsystem will
+regard it as the end of the file, unless you use
+L<C<binmode>|/binmode FILEHANDLE, LAYER>.
+
+L<C<binmode>|/binmode FILEHANDLE, LAYER> is important not only for
+L<C<readline>|/readline EXPR> and L<C<print>|/print FILEHANDLE LIST>
+operations, but also when using
+L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET> and
+L<C<tell>|/tell FILEHANDLE> (see L<perlport> for more details). See the
+L<C<$E<sol>>|perlvar/$E<sol>> and L<C<$\>|perlvar/$\> variables in
+L<perlvar> for how to manually set your input and output
line-termination sequences.
Portability issues: L<perlport/binmode>.
This function tells the thingy referenced by REF that it is now an object
in the CLASSNAME package. If CLASSNAME is omitted, the current package
-is used. Because a C<bless> is often the last thing in a constructor,
-it returns the reference for convenience. Always use the two-argument
-version if a derived class might inherit the function doing the blessing.
-See L<perlobj> for more about the blessing (and blessings) of objects.
+is used. Because a L<C<bless>|/bless REF,CLASSNAME> is often the last
+thing in a constructor, it returns the reference for convenience.
+Always use the two-argument version if a derived class might inherit the
+method doing the blessing. See L<perlobj> for more about the blessing
+(and blessings) of objects.
Consider always blessing objects in CLASSNAMEs that are mixed case.
Namespaces with all lowercase names are considered reserved for
-Perl pragmata. Builtin types have all uppercase names. To prevent
+Perl pragmas. Builtin types have all uppercase names. To prevent
confusion, you may wish to avoid such package names as well. Make sure
that CLASSNAME is a true value.
=for Pod::Functions +switch break out of a C<given> block
-Break out of a C<given()> block.
+Break out of a C<given> block.
-This keyword is enabled by the C<"switch"> feature; see L<feature> for
-more information on C<"switch">. You can also access it by prefixing it
-with C<CORE::>. Alternatively, include a C<use v5.10> or later to the
-current scope.
+L<C<break>|/break> is available only if the
+L<C<"switch"> feature|feature/The 'switch' feature> is enabled or if it
+is prefixed with C<CORE::>. The
+L<C<"switch"> feature|feature/The 'switch' feature> is enabled
+automatically with a C<use v5.10> (or higher) declaration in the current
+scope.
=item caller EXPR
X<caller> X<call stack> X<stack> X<stack trace>
Returns the context of the current pure perl subroutine call. In scalar
context, returns the caller's package name if there I<is> a caller (that is, if
-we're in a subroutine or C<eval> or C<require>) and the undefined value
-otherwise. caller never returns XS subs and they are skipped. The next pure
-perl sub will appear instead of the XS
-sub in caller's return values. In list
-context, caller returns
+we're in a subroutine or L<C<eval>|/eval EXPR> or
+L<C<require>|/require VERSION>) and the undefined value otherwise.
+caller never returns XS subs and they are skipped. The next pure perl
+sub will appear instead of the XS sub in caller's return values. In
+list context, caller returns
- # 0 1 2
- ($package, $filename, $line) = caller;
+ # 0 1 2
+ my ($package, $filename, $line) = caller;
With EXPR, it returns some extra information that the debugger uses to
print a stack trace. The value of EXPR indicates how many call frames
to go back before the current one.
# 0 1 2 3 4
- ($package, $filename, $line, $subroutine, $hasargs,
+ my ($package, $filename, $line, $subroutine, $hasargs,
# 5 6 7 8 9 10
$wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash)
- = caller($i);
+ = caller($i);
Here, $subroutine is the function that the caller called (rather than the
function containing the caller). Note that $subroutine may be C<(eval)> if
-the frame is not a subroutine call, but an C<eval>. In such a case
-additional elements $evaltext and
-C<$is_require> are set: C<$is_require> is true if the frame is created by a
-C<require> or C<use> statement, $evaltext contains the text of the
-C<eval EXPR> statement. In particular, for an C<eval BLOCK> statement,
-$subroutine is C<(eval)>, but $evaltext is undefined. (Note also that
-each C<use> statement creates a C<require> frame inside an C<eval EXPR>
-frame.) $subroutine may also be C<(unknown)> if this particular
-subroutine happens to have been deleted from the symbol table.
-C<$hasargs> is true if a new instance of C<@_> was set up for the frame.
+the frame is not a subroutine call, but an L<C<eval>|/eval EXPR>. In
+such a case additional elements $evaltext and C<$is_require> are set:
+C<$is_require> is true if the frame is created by a
+L<C<require>|/require VERSION> or L<C<use>|/use Module VERSION LIST>
+statement, $evaltext contains the text of the C<eval EXPR> statement.
+In particular, for an C<eval BLOCK> statement, $subroutine is C<(eval)>,
+but $evaltext is undefined. (Note also that each
+L<C<use>|/use Module VERSION LIST> statement creates a
+L<C<require>|/require VERSION> frame inside an C<eval EXPR> frame.)
+$subroutine may also be C<(unknown)> if this particular subroutine
+happens to have been deleted from the symbol table. C<$hasargs> is true
+if a new instance of L<C<@_>|perlvar/@_> was set up for the frame.
C<$hints> and C<$bitmask> contain pragmatic hints that the caller was
-compiled with. C<$hints> corresponds to C<$^H>, and C<$bitmask>
-corresponds to C<${^WARNING_BITS}>. The
-C<$hints> and C<$bitmask> values are subject
-to change between versions of Perl, and are not meant for external use.
-
-C<$hinthash> is a reference to a hash containing the value of C<%^H> when the
-caller was compiled, or C<undef> if C<%^H> was empty. Do not modify the values
-of this hash, as they are the actual values stored in the optree.
+compiled with. C<$hints> corresponds to L<C<$^H>|perlvar/$^H>, and
+C<$bitmask> corresponds to
+L<C<${^WARNING_BITS}>|perlvar/${^WARNING_BITS}>. The C<$hints> and
+C<$bitmask> values are subject to change between versions of Perl, and
+are not meant for external use.
+
+C<$hinthash> is a reference to a hash containing the value of
+L<C<%^H>|perlvar/%^H> when the caller was compiled, or
+L<C<undef>|/undef EXPR> if L<C<%^H>|perlvar/%^H> was empty. Do not
+modify the values of this hash, as they are the actual values stored in
+the optree.
Furthermore, when called from within the DB package in
list context, and with an argument, caller returns more
arguments with which the subroutine was invoked.
Be aware that the optimizer might have optimized call frames away before
-C<caller> had a chance to get the information. That means that C<caller(N)>
-might not return information about the call frame you expect it to, for
-C<< N > 1 >>. In particular, C<@DB::args> might have information from the
-previous time C<caller> was called.
+L<C<caller>|/caller EXPR> had a chance to get the information. That
+means that C<caller(N)> might not return information about the call
+frame you expect it to, for C<< N > 1 >>. In particular, C<@DB::args>
+might have information from the previous time L<C<caller>|/caller EXPR>
+was called.
Be aware that setting C<@DB::args> is I<best effort>, intended for
debugging or generating backtraces, and should not be relied upon. In
-particular, as C<@_> contains aliases to the caller's arguments, Perl does
-not take a copy of C<@_>, so C<@DB::args> will contain modifications the
-subroutine makes to C<@_> or its contents, not the original values at call
-time. C<@DB::args>, like C<@_>, does not hold explicit references to its
-elements, so under certain cases its elements may have become freed and
-reallocated for other variables or temporary values. Finally, a side effect
-of the current implementation is that the effects of C<shift @_> can
-I<normally> be undone (but not C<pop @_> or other splicing, I<and> not if a
-reference to C<@_> has been taken, I<and> subject to the caveat about reallocated
-elements), so C<@DB::args> is actually a hybrid of the current state and
-initial state of C<@_>. Buyer beware.
+particular, as L<C<@_>|perlvar/@_> contains aliases to the caller's
+arguments, Perl does not take a copy of L<C<@_>|perlvar/@_>, so
+C<@DB::args> will contain modifications the subroutine makes to
+L<C<@_>|perlvar/@_> or its contents, not the original values at call
+time. C<@DB::args>, like L<C<@_>|perlvar/@_>, does not hold explicit
+references to its elements, so under certain cases its elements may have
+become freed and reallocated for other variables or temporary values.
+Finally, a side effect of the current implementation is that the effects
+of C<shift @_> can I<normally> be undone (but not C<pop @_> or other
+splicing, I<and> not if a reference to L<C<@_>|perlvar/@_> has been
+taken, I<and> subject to the caveat about reallocated elements), so
+C<@DB::args> is actually a hybrid of the current state and initial state
+of L<C<@_>|perlvar/@_>. Buyer beware.
=item chdir EXPR
X<chdir>
Changes the working directory to EXPR, if possible. If EXPR is omitted,
changes to the directory specified by C<$ENV{HOME}>, if set; if not,
changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the
-variable C<$ENV{SYS$LOGIN}> is also checked, and used if it is set.) If
-neither is set, C<chdir> does nothing. It returns true on success,
-false otherwise. See the example under C<die>.
+variable C<$ENV{'SYS$LOGIN'}> is also checked, and used if it is set.) If
+neither is set, L<C<chdir>|/chdir EXPR> does nothing and fails. It
+returns true on success, false otherwise. See the example under
+L<C<die>|/die LIST>.
-On systems that support fchdir(2), you may pass a filehandle or
-directory handle as the argument. On systems that don't support fchdir(2),
+On systems that support L<fchdir(2)>, you may pass a filehandle or
+directory handle as the argument. On systems that don't support L<fchdir(2)>,
passing handles raises an exception.
=item chmod LIST
list must be the numeric mode, which should probably be an octal
number, and which definitely should I<not> be a string of octal digits:
C<0644> is okay, but C<"0644"> is not. Returns the number of files
-successfully changed. See also L</oct> if all you have is a string.
+successfully changed. See also L<C<oct>|/oct EXPR> if all you have is a
+string.
- $cnt = chmod 0755, "foo", "bar";
+ my $cnt = chmod 0755, "foo", "bar";
chmod 0755, @executables;
- $mode = "0644"; chmod $mode, "foo"; # !!! sets mode to
- # --w----r-T
- $mode = "0644"; chmod oct($mode), "foo"; # this is better
- $mode = 0644; chmod $mode, "foo"; # this is best
+ my $mode = "0644"; chmod $mode, "foo"; # !!! sets mode to
+ # --w----r-T
+ my $mode = "0644"; chmod oct($mode), "foo"; # this is better
+ my $mode = 0644; chmod $mode, "foo"; # this is best
-On systems that support fchmod(2), you may pass filehandles among the
-files. On systems that don't support fchmod(2), passing filehandles raises
+On systems that support L<fchmod(2)>, you may pass filehandles among the
+files. On systems that don't support L<fchmod(2)>, passing filehandles raises
an exception. Filehandles must be passed as globs or glob references to be
recognized; barewords are considered filenames.
my $perm = (stat $fh)[2] & 07777;
chmod($perm | 0600, $fh);
-You can also import the symbolic C<S_I*> constants from the C<Fcntl>
-module:
+You can also import the symbolic C<S_I*> constants from the
+L<C<Fcntl>|Fcntl> module:
use Fcntl qw( :mode );
chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
=for Pod::Functions remove a trailing record separator from a string
-This safer version of L</chop> removes any trailing string
-that corresponds to the current value of C<$/> (also known as
-$INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total
+This safer version of L<C<chop>|/chop VARIABLE> removes any trailing
+string that corresponds to the current value of
+L<C<$E<sol>>|perlvar/$E<sol>> (also known as C<$INPUT_RECORD_SEPARATOR>
+in the L<C<English>|English> module). It returns the total
number of characters removed from all its arguments. It's often used to
remove the newline from the end of an input record when you're worried
that the final record may be missing its newline. When in paragraph
-mode (C<$/ = "">), it removes all trailing newlines from the string.
-When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is
-a reference to an integer or the like; see L<perlvar>) chomp() won't
-remove anything.
-If VARIABLE is omitted, it chomps C<$_>. Example:
+mode (C<$/ = ''>), it removes all trailing newlines from the string.
+When in slurp mode (C<$/ = undef>) or fixed-length record mode
+(L<C<$E<sol>>|perlvar/$E<sol>> is a reference to an integer or the like;
+see L<perlvar>), L<C<chomp>|/chomp VARIABLE> won't remove anything.
+If VARIABLE is omitted, it chomps L<C<$_>|perlvar/$_>. Example:
while (<>) {
chomp; # avoid \n on last field
- @array = split(/:/);
+ my @array = split(/:/);
# ...
}
If VARIABLE is a hash, it chomps the hash's values, but not its keys,
-resetting the C<each> iterator in the process.
+resetting the L<C<each>|/each HASH> iterator in the process.
You can actually chomp anything that's an lvalue, including an assignment:
- chomp($cwd = `pwd`);
- chomp($answer = <STDIN>);
+ chomp(my $cwd = `pwd`);
+ chomp(my $answer = <STDIN>);
If you chomp a list, each element is chomped, and the total number of
characters removed is returned.
Chops off the last character of a string and returns the character
chopped. It is much more efficient than C<s/.$//s> because it neither
-scans nor copies the string. If VARIABLE is omitted, chops C<$_>.
+scans nor copies the string. If VARIABLE is omitted, chops
+L<C<$_>|perlvar/$_>.
If VARIABLE is a hash, it chops the hash's values, but not its keys,
-resetting the C<each> iterator in the process.
+resetting the L<C<each>|/each HASH> iterator in the process.
You can actually chop anything that's an lvalue, including an assignment.
If you chop a list, each element is chopped. Only the value of the
-last C<chop> is returned.
+last L<C<chop>|/chop VARIABLE> is returned.
-Note that C<chop> returns the last character. To return all but the last
-character, use C<substr($string, 0, -1)>.
+Note that L<C<chop>|/chop VARIABLE> returns the last character. To
+return all but the last character, use C<substr($string, 0, -1)>.
-See also L</chomp>.
+See also L<C<chomp>|/chomp VARIABLE>.
=item chown LIST
X<chown> X<owner> X<user> X<group>
systems to leave that value unchanged. Returns the number of files
successfully changed.
- $cnt = chown $uid, $gid, 'foo', 'bar';
+ my $cnt = chown $uid, $gid, 'foo', 'bar';
chown $uid, $gid, @filenames;
-On systems that support fchown(2), you may pass filehandles among the
-files. On systems that don't support fchown(2), passing filehandles raises
+On systems that support L<fchown(2)>, you may pass filehandles among the
+files. On systems that don't support L<fchown(2)>, passing filehandles raises
an exception. Filehandles must be passed as globs or glob references to be
recognized; barewords are considered filenames.
Here's an example that looks up nonnumeric uids in the passwd file:
print "User: ";
- chomp($user = <STDIN>);
+ chomp(my $user = <STDIN>);
print "Files: ";
- chomp($pattern = <STDIN>);
+ chomp(my $pattern = <STDIN>);
- ($login,$pass,$uid,$gid) = getpwnam($user)
+ my ($login,$pass,$uid,$gid) = getpwnam($user)
or die "$user not in passwd file";
- @ary = glob($pattern); # expand filenames
+ my @ary = glob($pattern); # expand filenames
chown $uid, $gid, @ary;
On most systems, you are not allowed to change the ownership of the
On POSIX systems, you can detect this condition this way:
use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
- $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);
+ my $can_chown_giveaway = ! sysconf(_PC_CHOWN_RESTRICTED);
Portability issues: L<perlport/chown>.
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
-chr(0x263a) is a Unicode smiley face.
+chr(0x263a) is a Unicode smiley face.
Negative values give the Unicode replacement character (chr(0xfffd)),
except under the L<bytes> pragma, where the low eight bits of the value
(truncated to an integer) are used.
-If NUMBER is omitted, uses C<$_>.
+If NUMBER is omitted, uses L<C<$_>|perlvar/$_>.
-For the reverse, use L</ord>.
+For the reverse, use L<C<ord>|/ord EXPR>.
Note that characters from 128 to 255 (inclusive) are by default
internally not encoded as UTF-8 for backward compatibility reasons.
begin with a C</> by your process and all its children. (It doesn't
change your current working directory, which is unaffected.) For security
reasons, this call is restricted to the superuser. If FILENAME is
-omitted, does a C<chroot> to C<$_>.
+omitted, does a L<C<chroot>|/chroot FILENAME> to L<C<$_>|perlvar/$_>.
-B<NOTE:> It is good security practice to do C<chdir("/")> (to the root
-directory) immediately after a C<chroot()>.
+B<NOTE:> It is good security practice to do C<chdir("/")>
+(L<C<chdir>|/chdir EXPR> to the root directory) immediately after a
+L<C<chroot>|/chroot FILENAME>.
Portability issues: L<perlport/chroot>.
omitted.
You don't have to close FILEHANDLE if you are immediately going to do
-another C<open> on it, because C<open> closes it for you. (See
-L<open|/open FILEHANDLE>.) However, an explicit C<close> on an input file resets the line
-counter (C<$.>), while the implicit close done by C<open> does not.
-
-If the filehandle came from a piped open, C<close> returns false if one of
-the other syscalls involved fails or if its program exits with non-zero
-status. If the only problem was that the program exited non-zero, C<$!>
-will be set to C<0>. Closing a pipe also waits for the process executing
-on the pipe to exit--in case you wish to look at the output of the pipe
-afterwards--and implicitly puts the exit status value of that command into
-C<$?> and C<${^CHILD_ERROR_NATIVE}>.
-
-If there are multiple threads running, C<close> on a filehandle from a
-piped open returns true without waiting for the child process to terminate,
-if the filehandle is still open in another thread.
+another L<C<open>|/open FILEHANDLE,EXPR> on it, because
+L<C<open>|/open FILEHANDLE,EXPR> closes it for you. (See
+L<C<open>|/open FILEHANDLE,EXPR>.) However, an explicit
+L<C<close>|/close FILEHANDLE> on an input file resets the line counter
+(L<C<$.>|perlvar/$.>), while the implicit close done by
+L<C<open>|/open FILEHANDLE,EXPR> does not.
+
+If the filehandle came from a piped open, L<C<close>|/close FILEHANDLE>
+returns false if one of the other syscalls involved fails or if its
+program exits with non-zero status. If the only problem was that the
+program exited non-zero, L<C<$!>|perlvar/$!> will be set to C<0>.
+Closing a pipe also waits for the process executing on the pipe to
+exit--in case you wish to look at the output of the pipe afterwards--and
+implicitly puts the exit status value of that command into
+L<C<$?>|perlvar/$?> and
+L<C<${^CHILD_ERROR_NATIVE}>|perlvar/${^CHILD_ERROR_NATIVE}>.
+
+If there are multiple threads running, L<C<close>|/close FILEHANDLE> on
+a filehandle from a piped open returns true without waiting for the
+child process to terminate, if the filehandle is still open in another
+thread.
Closing the read end of a pipe before the process writing to it at the
other end is done writing results in the writer receiving a SIGPIPE. If
=for Pod::Functions close directory handle
-Closes a directory opened by C<opendir> and returns the success of that
-system call.
+Closes a directory opened by L<C<opendir>|/opendir DIRHANDLE,EXPR> and
+returns the success of that system call.
=item connect SOCKET,NAME
X<connect>
=for Pod::Functions connect to a remote socket
-Attempts to connect to a remote socket, just like connect(2).
+Attempts to connect to a remote socket, just like L<connect(2)>.
Returns true if it succeeded, false otherwise. NAME should be a
packed address of the appropriate type for the socket. See the examples in
L<perlipc/"Sockets: Client/Server Communication">.
=for Pod::Functions optional trailing block in a while or foreach
-When followed by a BLOCK, C<continue> is actually a
-flow control statement rather than a function. If
-there is a C<continue> BLOCK attached to a BLOCK (typically in a C<while> or
-C<foreach>), it is always executed just before the conditional is about to
-be evaluated again, just like the third part of a C<for> loop in C. Thus
-it can be used to increment a loop variable, even when the loop has been
-continued via the C<next> statement (which is similar to the C C<continue>
+When followed by a BLOCK, L<C<continue>|/continue BLOCK> is actually a
+flow control statement rather than a function. If there is a
+L<C<continue>|/continue BLOCK> BLOCK attached to a BLOCK (typically in a
+C<while> or C<foreach>), it is always executed just before the
+conditional is about to be evaluated again, just like the third part of
+a C<for> loop in C. Thus it can be used to increment a loop variable,
+even when the loop has been continued via the L<C<next>|/next LABEL>
+statement (which is similar to the C L<C<continue>|/continue BLOCK>
statement).
-C<last>, C<next>, or C<redo> may appear within a C<continue>
-block; C<last> and C<redo> behave as if they had been executed within
-the main block. So will C<next>, but since it will execute a C<continue>
-block, it may be more entertaining.
+L<C<last>|/last LABEL>, L<C<next>|/next LABEL>, or
+L<C<redo>|/redo LABEL> may appear within a
+L<C<continue>|/continue BLOCK> block; L<C<last>|/last LABEL> and
+L<C<redo>|/redo LABEL> behave as if they had been executed within the
+main block. So will L<C<next>|/next LABEL>, but since it will execute a
+L<C<continue>|/continue BLOCK> block, it may be more entertaining.
while (EXPR) {
### redo always comes here
}
### last always comes here
-Omitting the C<continue> section is equivalent to using an
-empty one, logically enough, so C<next> goes directly back
-to check the condition at the top of the loop.
+Omitting the L<C<continue>|/continue BLOCK> section is equivalent to
+using an empty one, logically enough, so L<C<next>|/next LABEL> goes
+directly back to check the condition at the top of the loop.
-When there is no BLOCK, C<continue> is a function that
-falls through the current C<when> or C<default> block instead of iterating
-a dynamically enclosing C<foreach> or exiting a lexically enclosing C<given>.
-In Perl 5.14 and earlier, this form of C<continue> was
-only available when the C<"switch"> feature was enabled.
-See L<feature> and L<perlsyn/"Switch Statements"> for more
-information.
+When there is no BLOCK, L<C<continue>|/continue BLOCK> is a function
+that falls through the current C<when> or C<default> block instead of
+iterating a dynamically enclosing C<foreach> or exiting a lexically
+enclosing C<given>. In Perl 5.14 and earlier, this form of
+L<C<continue>|/continue BLOCK> was only available when the
+L<C<"switch"> feature|feature/The 'switch' feature> was enabled. See
+L<feature> and L<perlsyn/"Switch Statements"> for more information.
=item cos EXPR
X<cos> X<cosine> X<acos> X<arccosine>
=for Pod::Functions cosine function
Returns the cosine of EXPR (expressed in radians). If EXPR is omitted,
-takes the cosine of C<$_>.
+takes the cosine of L<C<$_>|perlvar/$_>.
-For the inverse cosine operation, you may use the C<Math::Trig::acos()>
-function, or use this relation:
+For the inverse cosine operation, you may use the
+L<C<Math::Trig::acos>|Math::Trig> function, or use this relation:
sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }
=for Pod::Functions one-way passwd-style encryption
-Creates a digest string exactly like the crypt(3) function in the C
+Creates a digest string exactly like the L<crypt(3)> function in the C
library (assuming that you actually have a version there that has not
been extirpated as a potential munition).
-crypt() is a one-way hash function. The PLAINTEXT and SALT are turned
+L<C<crypt>|/crypt PLAINTEXT,SALT> is a one-way hash function. The
+PLAINTEXT and SALT are turned
into a short string, called a digest, which is returned. The same
PLAINTEXT and SALT will always return the same string, but there is no
(known) way to get the original PLAINTEXT from the hash. Small
having to transmit or store the text itself. An example is checking
if a correct password is given. The digest of the password is stored,
not the password itself. The user types in a password that is
-crypt()'d with the same salt as the stored digest. If the two digests
-match, the password is correct.
+L<C<crypt>|/crypt PLAINTEXT,SALT>'d with the same salt as the stored
+digest. If the two digests match, the password is correct.
When verifying an existing digest string you should use the digest as
the salt (like C<crypt($plain, $digest) eq $digest>). The SALT used
to create the digest is visible as part of the digest. This ensures
-crypt() will hash the new string with the same salt as the digest.
-This allows your code to work with the standard L<crypt|/crypt> and
-with more exotic implementations. In other words, assume
-nothing about the returned string itself nor about how many bytes
-of SALT may matter.
+L<C<crypt>|/crypt PLAINTEXT,SALT> will hash the new string with the same
+salt as the digest. This allows your code to work with the standard
+L<C<crypt>|/crypt PLAINTEXT,SALT> and with more exotic implementations.
+In other words, assume nothing about the returned string itself nor
+about how many bytes of SALT may matter.
Traditionally the result is a string of 13 bytes: two first bytes of
the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only
'/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>). This set of
characters is just a recommendation; the characters allowed in
the salt depend solely on your system's crypt library, and Perl can't
-restrict what salts C<crypt()> accepts.
+restrict what salts L<C<crypt>|/crypt PLAINTEXT,SALT> accepts.
Here's an example that makes sure that whoever runs this program knows
their password:
- $pwd = (getpwuid($<))[1];
+ my $pwd = (getpwuid($<))[1];
system "stty -echo";
print "Password: ";
- chomp($word = <STDIN>);
+ chomp(my $word = <STDIN>);
print "\n";
system "stty echo";
Of course, typing in your own password to whoever asks you
for it is unwise.
-The L<crypt|/crypt> function is unsuitable for hashing large quantities
-of data, not least of all because you can't get the information
-back. Look at the L<Digest> module for more robust algorithms.
+The L<C<crypt>|/crypt PLAINTEXT,SALT> function is unsuitable for hashing
+large quantities of data, not least of all because you can't get the
+information back. Look at the L<Digest> module for more robust
+algorithms.
-If using crypt() on a Unicode string (which I<potentially> has
-characters with codepoints above 255), Perl tries to make sense
-of the situation by trying to downgrade (a copy of)
-the string back to an eight-bit byte string before calling crypt()
-(on that copy). If that works, good. If not, crypt() dies with
-C<Wide character in crypt>.
+If using L<C<crypt>|/crypt PLAINTEXT,SALT> on a Unicode string (which
+I<potentially> has characters with codepoints above 255), Perl tries to
+make sense of the situation by trying to downgrade (a copy of) the
+string back to an eight-bit byte string before calling
+L<C<crypt>|/crypt PLAINTEXT,SALT> (on that copy). If that works, good.
+If not, L<C<crypt>|/crypt PLAINTEXT,SALT> dies with
+L<C<Wide character in crypt>|perldiag/Wide character in %s>.
Portability issues: L<perlport/crypt>.
=for Pod::Functions breaks binding on a tied dbm file
-[This function has been largely superseded by the C<untie> function.]
+[This function has been largely superseded by the
+L<C<untie>|/untie VARIABLE> function.]
Breaks the binding between a DBM file and a hash.
=for Pod::Functions create binding on a tied dbm file
[This function has been largely superseded by the
-L<tie|/tie VARIABLE,CLASSNAME,LIST> function.]
-
-This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a
-hash. HASH is the name of the hash. (Unlike normal C<open>, the first
-argument is I<not> a filehandle, even though it looks like one). DBNAME
-is the name of the database (without the F<.dir> or F<.pag> extension if
-any). If the database does not exist, it is created with protection
-specified by MASK (as modified by the C<umask>). To prevent creation of
-the database if it doesn't exist, you may specify a MODE
-of 0, and the function will return a false value if it
-can't find an existing database. If your system supports
-only the older DBM functions, you may make only one C<dbmopen> call in your
+L<C<tie>|/tie VARIABLE,CLASSNAME,LIST> function.]
+
+This binds a L<dbm(3)>, L<ndbm(3)>, L<sdbm(3)>, L<gdbm(3)>, or Berkeley
+DB file to a hash. HASH is the name of the hash. (Unlike normal
+L<C<open>|/open FILEHANDLE,EXPR>, the first argument is I<not> a
+filehandle, even though it looks like one). DBNAME is the name of the
+database (without the F<.dir> or F<.pag> extension if any). If the
+database does not exist, it is created with protection specified by MASK
+(as modified by the L<C<umask>|/umask EXPR>). To prevent creation of
+the database if it doesn't exist, you may specify a MODE of 0, and the
+function will return a false value if it can't find an existing
+database. If your system supports only the older DBM functions, you may
+make only one L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK> call in your
program. In older versions of Perl, if your system had neither DBM nor
-ndbm, calling C<dbmopen> produced a fatal error; it now falls back to
-sdbm(3).
+ndbm, calling L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK> produced a fatal
+error; it now falls back to L<sdbm(3)>.
If you don't have write access to the DBM file, you can only read hash
variables, not set them. If you want to test whether you can write,
-either use file tests or try setting a dummy hash entry inside an C<eval>
-to trap the error.
+either use file tests or try setting a dummy hash entry inside an
+L<C<eval>|/eval EXPR> to trap the error.
-Note that functions such as C<keys> and C<values> may return huge lists
-when used on large DBM files. You may prefer to use the C<each>
-function to iterate over large DBM files. Example:
+Note that functions such as L<C<keys>|/keys HASH> and
+L<C<values>|/values HASH> may return huge lists when used on large DBM
+files. You may prefer to use the L<C<each>|/each HASH> function to
+iterate over large DBM files. Example:
# print out history file offsets
dbmopen(%HIST,'/usr/lib/news/history',0666);
rich implementation.
You can control which DBM library you use by loading that library
-before you call dbmopen():
+before you call L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK>:
use DB_File;
dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
=for Pod::Functions test whether a value, variable, or function is defined
-Returns a Boolean value telling whether EXPR has a value other than
-the undefined value C<undef>. If EXPR is not present, C<$_> is
-checked.
-
-Many operations return C<undef> to indicate failure, end of file,
-system error, uninitialized variable, and other exceptional
-conditions. This function allows you to distinguish C<undef> from
-other values. (A simple Boolean test will not distinguish among
-C<undef>, zero, the empty string, and C<"0">, which are all equally
-false.) Note that since C<undef> is a valid scalar, its presence
-doesn't I<necessarily> indicate an exceptional condition: C<pop>
-returns C<undef> when its argument is an empty array, I<or> when the
-element to return happens to be C<undef>.
-
-You may also use C<defined(&func)> to check whether subroutine C<&func>
+Returns a Boolean value telling whether EXPR has a value other than the
+undefined value L<C<undef>|/undef EXPR>. If EXPR is not present,
+L<C<$_>|perlvar/$_> is checked.
+
+Many operations return L<C<undef>|/undef EXPR> to indicate failure, end
+of file, system error, uninitialized variable, and other exceptional
+conditions. This function allows you to distinguish
+L<C<undef>|/undef EXPR> from other values. (A simple Boolean test will
+not distinguish among L<C<undef>|/undef EXPR>, zero, the empty string,
+and C<"0">, which are all equally false.) Note that since
+L<C<undef>|/undef EXPR> is a valid scalar, its presence doesn't
+I<necessarily> indicate an exceptional condition: L<C<pop>|/pop ARRAY>
+returns L<C<undef>|/undef EXPR> when its argument is an empty array,
+I<or> when the element to return happens to be L<C<undef>|/undef EXPR>.
+
+You may also use C<defined(&func)> to check whether subroutine C<func>
has ever been defined. The return value is unaffected by any forward
-declarations of C<&func>. A subroutine that is not defined
+declarations of C<func>. A subroutine that is not defined
may still be callable: its package may have an C<AUTOLOAD> method that
makes it spring into existence the first time that it is called; see
L<perlsub>.
-Use of C<defined> on aggregates (hashes and arrays) is deprecated. It
+Use of L<C<defined>|/defined EXPR> on aggregates (hashes and arrays) is
+deprecated. It
used to report whether memory for that aggregate had ever been
allocated. This behavior may disappear in future versions of Perl.
You should instead use a simple test for size:
if (%a_hash) { print "has hash members\n" }
When used on a hash element, it tells you whether the value is defined,
-not whether the key exists in the hash. Use L</exists> for the latter
-purpose.
+not whether the key exists in the hash. Use L<C<exists>|/exists EXPR>
+for the latter purpose.
Examples:
print "$val\n" while defined($val = pop(@ary));
die "Can't readlink $sym: $!"
unless defined($value = readlink $sym);
- sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
+ sub foo { defined &$bar ? $bar->(@_) : die "No bar"; }
$debugging = 0 unless defined $debugging;
-Note: Many folks tend to overuse C<defined> and are then surprised to
-discover that the number C<0> and C<""> (the zero-length string) are, in fact,
-defined values. For example, if you say
+Note: Many folks tend to overuse L<C<defined>|/defined EXPR> and are
+then surprised to discover that the number C<0> and C<""> (the
+zero-length string) are, in fact, defined values. For example, if you
+say
"ab" =~ /a(.*)b/;
matched something that happened to be zero characters long. This is all
very above-board and honest. When a function returns an undefined value,
it's an admission that it couldn't give you an honest answer. So you
-should use C<defined> only when questioning the integrity of what
-you're trying to do. At other times, a simple comparison to C<0> or C<""> is
-what you want.
+should use L<C<defined>|/defined EXPR> only when questioning the
+integrity of what you're trying to do. At other times, a simple
+comparison to C<0> or C<""> is what you want.
-See also L</undef>, L</exists>, L</ref>.
+See also L<C<undef>|/undef EXPR>, L<C<exists>|/exists EXPR>,
+L<C<ref>|/ref EXPR>.
=item delete EXPR
X<delete>
=for Pod::Functions deletes a value from a hash
-Given an expression that specifies an element or slice of a hash, C<delete>
-deletes the specified elements from that hash so that exists() on that element
-no longer returns true. Setting a hash element to the undefined value does
-not remove its key, but deleting it does; see L</exists>.
+Given an expression that specifies an element or slice of a hash,
+L<C<delete>|/delete EXPR> deletes the specified elements from that hash
+so that L<C<exists>|/exists EXPR> on that element no longer returns
+true. Setting a hash element to the undefined value does not remove its
+key, but deleting it does; see L<C<exists>|/exists EXPR>.
In list context, returns the value or values deleted, or the last such
element in scalar context. The return list's length always matches that of
the argument list: deleting non-existent elements returns the undefined value
in their corresponding positions.
-delete() may also be used on arrays and array slices, but its behavior is less
-straightforward. Although exists() will return false for deleted entries,
-deleting array elements never changes indices of existing values; use shift()
-or splice() for that. However, if any deleted elements fall at the end of an
-array, the array's size shrinks to the position of the highest element that
-still tests true for exists(), or to 0 if none do. In other words, an
-array won't have trailing nonexistent elements after a delete.
-
-B<WARNING:> Calling C<delete> on array values is strongly discouraged. The
+L<C<delete>|/delete EXPR> may also be used on arrays and array slices,
+but its behavior is less straightforward. Although
+L<C<exists>|/exists EXPR> will return false for deleted entries,
+deleting array elements never changes indices of existing values; use
+L<C<shift>|/shift ARRAY> or L<C<splice>|/splice
+ARRAY,OFFSET,LENGTH,LIST> for that. However, if any deleted elements
+fall at the end of an array, the array's size shrinks to the position of
+the highest element that still tests true for L<C<exists>|/exists EXPR>,
+or to 0 if none do. In other words, an array won't have trailing
+nonexistent elements after a delete.
+
+B<WARNING:> Calling L<C<delete>|/delete EXPR> on array values is
+strongly discouraged. The
notion of deleting or checking the existence of Perl array elements is not
conceptually coherent, and can lead to surprising behavior.
-Deleting from C<%ENV> modifies the environment. Deleting from a hash tied to
-a DBM file deletes the entry from the DBM file. Deleting from a C<tied> hash
-or array may not necessarily return anything; it depends on the implementation
-of the C<tied> package's DELETE method, which may do whatever it pleases.
+Deleting from L<C<%ENV>|perlvar/%ENV> modifies the environment.
+Deleting from a hash tied to a DBM file deletes the entry from the DBM
+file. Deleting from a L<C<tied>|/tied VARIABLE> hash or array may not
+necessarily return anything; it depends on the implementation of the
+L<C<tied>|/tied VARIABLE> package's DELETE method, which may do whatever
+it pleases.
The C<delete local EXPR> construct localizes the deletion to the current
block at run time. Until the block exits, elements locally deleted
temporarily no longer exist. See L<perlsub/"Localized deletion of elements
of composite types">.
- %hash = (foo => 11, bar => 22, baz => 33);
- $scalar = delete $hash{foo}; # $scalar is 11
+ my %hash = (foo => 11, bar => 22, baz => 33);
+ my $scalar = delete $hash{foo}; # $scalar is 11
$scalar = delete @hash{qw(foo bar)}; # $scalar is 22
- @array = delete @hash{qw(foo baz)}; # @array is (undef,33)
+ my @array = delete @hash{qw(foo baz)}; # @array is (undef,33)
The following (inefficiently) deletes all the values of %HASH and @ARRAY:
- foreach $key (keys %HASH) {
+ foreach my $key (keys %HASH) {
delete $HASH{$key};
}
- foreach $index (0 .. $#ARRAY) {
+ foreach my $index (0 .. $#ARRAY) {
delete $ARRAY[$index];
}
delete @ARRAY[0 .. $#ARRAY];
But both are slower than assigning the empty list
-or undefining %HASH or @ARRAY, which is the customary
+or undefining %HASH or @ARRAY, which is the customary
way to empty out an aggregate:
%HASH = (); # completely empty %HASH
=for Pod::Functions raise an exception or bail out
-C<die> raises an exception. Inside an C<eval> the error message is stuffed
-into C<$@> and the C<eval> is terminated with the undefined value.
-If the exception is outside of all enclosing C<eval>s, then the uncaught
-exception prints LIST to C<STDERR> and exits with a non-zero value. If you
-need to exit the process with a specific exit code, see L</exit>.
+L<C<die>|/die LIST> raises an exception. Inside an
+L<C<eval>|/eval EXPR> the error message is stuffed into
+L<C<$@>|perlvar/$@> and the L<C<eval>|/eval EXPR> is terminated with the
+undefined value. If the exception is outside of all enclosing
+L<C<eval>|/eval EXPR>s, then the uncaught exception prints LIST to
+C<STDERR> and exits with a non-zero value. If you need to exit the
+process with a specific exit code, see L<C<exit>|/exit EXPR>.
Equivalent examples:
and a newline is supplied. Note that the "input line number" (also
known as "chunk") is subject to whatever notion of "line" happens to
be currently in effect, and is also available as the special variable
-
C<$.>. See L<perlvar/"$/"> and L<perlvar/"$.">.
+
L<C<$.>|perlvar/$.>. See L<perlvar/"$/"> and L<perlvar/"$.">.
Hint: sometimes appending C<", stopped"> to your message will cause it
to make better sense when the string C<"at foo line 123"> is appended.
/etc/games is no good at canasta line 123.
/etc/games is no good, stopped at canasta line 123.
-If the output is empty and C<$@> already contains a value (typically from a
-previous eval) that value is reused after appending C<"\t...propagated">.
-This is useful for propagating exceptions:
+If the output is empty and L<C<$@>|perlvar/$@> already contains a value
+(typically from a previous L<C<eval>|/eval EXPR>) that value is reused after
+appending C<"\t...propagated">. This is useful for propagating exceptions:
eval { ... };
die unless $@ =~ /Expected exception/;
-If the output is empty and C<$@> contains an object reference that has a
-C<PROPAGATE> method, that method will be called with additional file
-and line number parameters. The return value replaces the value in
-C<$@>; i.e., as if C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >>
-were called.
+If the output is empty and L<C<$@>|perlvar/$@> contains an object
+reference that has a C<PROPAGATE> method, that method will be called
+with additional file and line number parameters. The return value
+replaces the value in L<C<$@>|perlvar/$@>; i.e., as if
+C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >> were called.
-If C<$@> is empty then the string C<"Died"> is used.
+If L<C<$@>|perlvar/$@> is empty, then the string C<"Died"> is used.
If an uncaught exception results in interpreter exit, the exit code is
-determined from the values of C<$!> and C<$?> with this pseudocode:
+determined from the values of L<C<$!>|perlvar/$!> and
+L<C<$?>|perlvar/$?> with this pseudocode:
exit $! if $!; # errno
exit $? >> 8 if $? >> 8; # child exit status
exit 255; # last resort
+As with L<C<exit>|/exit EXPR>, L<C<$?>|perlvar/$?> is set prior to
+unwinding the call stack; any C<DESTROY> or C<END> handlers can then
+alter this value, and thus Perl's exit code.
+
The intent is to squeeze as much possible information about the likely cause
-into the limited space of the system exit
-code. However, as C<$!> is the value
-of C's C<errno>, which can be set by any system call, this means that the value
-of the exit code used by C<die> can be non-predictable, so should not be relied
+into the limited space of the system exit code. However, as
+L<C<$!>|perlvar/$!> is the value of C's C<errno>, which can be set by
+any system call, this means that the value of the exit code used by
+L<C<die>|/die LIST> can be non-predictable, so should not be relied
upon, other than to be non-zero.
-You can also call C<die> with a reference argument, and if this is trapped
-within an C<eval>, C<$@> contains that reference. This permits more
-elaborate exception handling using objects that maintain arbitrary state
-about the exception. Such a scheme is sometimes preferable to matching
-particular string values of C<$@> with regular expressions. Because C<$@>
-is a global variable and C<eval> may be used within object implementations,
-be careful that analyzing the error object doesn't replace the reference in
-the global variable. It's easiest to make a local copy of the reference
-before any manipulations. Here's an example:
+You can also call L<C<die>|/die LIST> with a reference argument, and if
+this is trapped within an L<C<eval>|/eval EXPR>, L<C<$@>|perlvar/$@>
+contains that reference. This permits more elaborate exception handling
+using objects that maintain arbitrary state about the exception. Such a
+scheme is sometimes preferable to matching particular string values of
+L<C<$@>|perlvar/$@> with regular expressions. Because
+L<C<$@>|perlvar/$@> is a global variable and L<C<eval>|/eval EXPR> may
+be used within object implementations, be careful that analyzing the
+error object doesn't replace the reference in the global variable. It's
+easiest to make a local copy of the reference before any manipulations.
+Here's an example:
use Scalar::Util "blessed";
you'll probably want to overload stringification operations on
exception objects. See L<overload> for details about that.
-You can arrange for a callback to be run just before the C<die>
-does its deed, by setting the C<$SIG{__DIE__}> hook. The associated
-handler is called with the error text and can change the error
-message, if it sees fit, by calling C<die> again. See
-L<perlvar/%SIG> for details on setting C<%SIG> entries, and
-L<"eval BLOCK"> for some examples. Although this feature was
-to be run only right before your program was to exit, this is not
-currently so: the C<$SIG{__DIE__}> hook is currently called
-even inside eval()ed blocks/strings! If one wants the hook to do
+You can arrange for a callback to be run just before the
+L<C<die>|/die LIST> does its deed, by setting the
+L<C<$SIG{__DIE__}>|perlvar/%SIG> hook. The associated handler is called
+with the error text and can change the error message, if it sees fit, by
+calling L<C<die>|/die LIST> again. See L<perlvar/%SIG> for details on
+setting L<C<%SIG>|perlvar/%SIG> entries, and L<C<eval>|/eval EXPR> for some
+examples. Although this feature was to be run only right before your
+program was to exit, this is not currently so: the
+L<C<$SIG{__DIE__}>|perlvar/%SIG> hook is currently called even inside
+L<C<eval>|/eval EXPR>ed blocks/strings! If one wants the hook to do
nothing in such situations, put
die @_ if $^S;
this promotes strange action at a distance, this counterintuitive
behavior may be fixed in a future release.
-See also exit(), warn(), and the Carp module.
+See also L<C<exit>|/exit EXPR>, L<C<warn>|/warn LIST>, and the L<Carp>
+module.
=item do BLOCK
X<do> X<block>
first.)
C<do BLOCK> does I<not> count as a loop, so the loop control statements
-C<next>, C<last>, or C<redo> cannot be used to leave or restart the block.
+L<C<next>|/next LABEL>, L<C<last>|/last LABEL>, or
+L<C<redo>|/redo LABEL> cannot be used to leave or restart the block.
See L<perlsyn> for alternative strategies.
=item do EXPR
eval `cat stat.pl`;
except that it's more concise, runs no external processes, keeps track of
-the current
-filename for error messages, searches the C<@INC> directories, and updates
-C<%INC> if the file is found. See L<perlvar/@INC> and L<perlvar/%INC> for
-these variables. It also differs in that code evaluated with C<do FILENAME>
-cannot see lexicals in the enclosing scope; C<eval STRING> does. It's the
-same, however, in that it does reparse the file every time you call it,
-so you probably don't want to do this inside a loop.
-
-If C<do> can read the file but cannot compile it, it returns C<undef> and sets
-an error message in C<$@>. If C<do> cannot read the file, it returns undef
-and sets C<$!> to the error. Always check C<$@> first, as compilation
-could fail in a way that also sets C<$!>. If the file is successfully
-compiled, C<do> returns the value of the last expression evaluated.
+the current filename for error messages, searches the
+L<C<@INC>|perlvar/@INC> directories, and updates L<C<%INC>|perlvar/%INC>
+if the file is found. See L<perlvar/@INC> and L<perlvar/%INC> for these
+variables. It also differs in that code evaluated with C<do FILE>
+cannot see lexicals in the enclosing scope; C<eval STRING> does. It's
+the same, however, in that it does reparse the file every time you call
+it, so you probably don't want to do this inside a loop.
+
+If L<C<do>|/do EXPR> can read the file but cannot compile it, it
+returns L<C<undef>|/undef EXPR> and sets an error message in
+L<C<$@>|perlvar/$@>. If L<C<do>|/do EXPR> cannot read the file, it
+returns undef and sets L<C<$!>|perlvar/$!> to the error. Always check
+L<C<$@>|perlvar/$@> first, as compilation could fail in a way that also
+sets L<C<$!>|perlvar/$!>. If the file is successfully compiled,
+L<C<do>|/do EXPR> returns the value of the last expression evaluated.
Inclusion of library modules is better done with the
-C<use> and C<require> operators, which also do automatic error checking
-and raise an exception if there's a problem.
+L<C<use>|/use Module VERSION LIST> and L<C<require>|/require VERSION>
+operators, which also do automatic error checking and raise an exception
+if there's a problem.
-You might like to use C<do> to read in a program configuration
-file. Manual error checking can be done this way:
+You might like to use L<C<do>|/do EXPR> to read in a program
+configuration file. Manual error checking can be done this way:
# read in config files: system first, then user
for $file ("/share/prog/defaults.rc",
supplied) to turn your core dump into an executable binary after
having initialized all your variables at the beginning of the
program. When the new binary is executed it will begin by executing
-a C<goto LABEL> (with all the restrictions that C<goto> suffers).
+a C<goto LABEL> (with all the restrictions that L<C<goto>|/goto LABEL>
+suffers).
Think of it as a goto with an intervening core dump and reincarnation.
If C<LABEL> is omitted, restarts the program from the top. The
C<dump EXPR> form, available starting in Perl 5.18.0, allows a name to be
This function is now largely obsolete, mostly because it's very hard to
convert a core file into an executable. That's why you should now invoke
-it as C<CORE::dump()>, if you don't want to be warned against a possible
+it as C<CORE::dump()> if you don't want to be warned against a possible
typo.
Unlike most named operators, this has the same precedence as assignment.
It is also exempt from the looks-like-a-function rule, so
C<dump ("foo")."bar"> will cause "bar" to be part of the argument to
-C<dump>.
+L<C<dump>|/dump LABEL>.
Portability issues: L<perlport/dump>.
=item each ARRAY
X<array, iterator>
-=item each EXPR
-
=for Pod::Functions retrieve the next key/value pair from a hash
When called on a hash in list context, returns a 2-element list
order is specific to a given hash; the exact same series of operations
on two hashes may result in a different order for each hash. Any insertion
into the hash may change the order, as will any deletion, with the exception
-that the most recent key returned by C<each> or C<keys> may be deleted
-without changing the order. So long as a given hash is unmodified you may
-rely on C<keys>, C<values> and C<each> to repeatedly return the same order
+that the most recent key returned by L<C<each>|/each HASH> or
+L<C<keys>|/keys HASH> may be deleted without changing the order. So
+long as a given hash is unmodified you may rely on
+L<C<keys>|/keys HASH>, L<C<values>|/values HASH> and
+L<C<each>|/each HASH> to repeatedly return the same order
as each other. See L<perlsec/"Algorithmic Complexity Attacks"> for
details on why hash order is randomized. Aside from the guarantees
provided here the exact details of Perl's hash algorithm and the hash
traversal order are subject to change in any release of Perl.
-After C<each> has returned all entries from the hash or array, the next
-call to C<each> returns the empty list in list context and C<undef> in
-scalar context; the next call following I<that> one restarts iteration.
-Each hash or array has its own internal iterator, accessed by C<each>,
-C<keys>, and C<values>. The iterator is implicitly reset when C<each> has
-reached the end as just described; it can be explicitly reset by calling
-C<keys> or C<values> on the hash or array. If you add or delete a hash's
-elements while iterating over it, the effect on the iterator is
+After L<C<each>|/each HASH> has returned all entries from the hash or
+array, the next call to L<C<each>|/each HASH> returns the empty list in
+list context and L<C<undef>|/undef EXPR> in scalar context; the next
+call following I<that> one restarts iteration. Each hash or array has
+its own internal iterator, accessed by L<C<each>|/each HASH>,
+L<C<keys>|/keys HASH>, and L<C<values>|/values HASH>. The iterator is
+implicitly reset when L<C<each>|/each HASH> has reached the end as just
+described; it can be explicitly reset by calling L<C<keys>|/keys HASH>
+or L<C<values>|/values HASH> on the hash or array. If you add or delete
+a hash's elements while iterating over it, the effect on the iterator is
unspecified; for example, entries may be skipped or duplicated--so don't
do that. Exception: It is always safe to delete the item most recently
-returned by C<each()>, so the following code works properly:
+returned by L<C<each>|/each HASH>, so the following code works properly:
- while (($key, $value) = each %hash) {
- print $key, "\n";
- delete $hash{$key}; # This is safe
- }
+ while (my ($key, $value) = each %hash) {
+ print $key, "\n";
+ delete $hash{$key}; # This is safe
+ }
Tied hashes may have a different ordering behaviour to perl's hash
implementation.
-This prints out your environment like the printenv(1) program,
+This prints out your environment like the L<printenv(1)> program,
but in a different order:
- while (($key,$value) = each %ENV) {
+ while (my ($key,$value) = each %ENV) {
print "$key=$value\n";
}
-Starting with Perl 5.14, C<each> can take a scalar EXPR, which must hold
-reference to an unblessed hash or array. The argument will be dereferenced
-automatically. This aspect of C<each> is considered highly experimental.
-The exact behaviour may change in a future version of Perl.
-
- while (($key,$value) = each $hashref) { ... }
+Starting with Perl 5.14, an experimental feature allowed
+L<C<each>|/each HASH> to take a scalar expression. This experiment has
+been deemed unsuccessful, and was removed as of Perl 5.24.
-As of Perl 5.18 you can use a bare C<each> in a C<while> loop,
-which will set C<$_> on every iteration.
+As of Perl 5.18 you can use a bare L<C<each>|/each HASH> in a C<while>
+loop, which will set L<C<$_>|perlvar/$_> on every iteration.
- while(each %ENV) {
+ while (each %ENV) {
print "$_=$ENV{$_}\n";
}
a recent vintage:
use 5.012; # so keys/values/each work on arrays
- use 5.014; # so keys/values/each work on scalars (experimental)
use 5.018; # so each assigns to $_ in a lone while test
-See also C<keys>, C<values>, and C<sort>.
+See also L<C<keys>|/keys HASH>, L<C<values>|/values HASH>, and
+L<C<sort>|/sort SUBNAME LIST>.
=item eof FILEHANDLE
X<eof>
C<eof(FILEHANDLE)> on it) after end-of-file is reached. File types such
as terminals may lose the end-of-file condition if you do.
-An C<eof> without an argument uses the last file read. Using C<eof()>
-with empty parentheses is different. It refers to the pseudo file
-formed from the files listed on the command line and accessed via the
-C<< <> >> operator. Since C<< <> >> isn't explicitly opened,
-as a normal filehandle is, an C<eof()> before C<< <> >> has been
-used will cause C<@ARGV> to be examined to determine if input is
-available. Similarly, an C<eof()> after C<< <> >> has returned
-end-of-file will assume you are processing another C<@ARGV> list,
-and if you haven't set C<@ARGV>, will read input from C<STDIN>;
-see L<perlop/"I/O Operators">.
-
-In a C<< while (<>) >> loop, C<eof> or C<eof(ARGV)> can be used to
-detect the end of each file, whereas C<eof()> will detect the end
-of the very last file only. Examples:
+An L<C<eof>|/eof FILEHANDLE> without an argument uses the last file
+read. Using L<C<eof()>|/eof FILEHANDLE> with empty parentheses is
+different. It refers to the pseudo file formed from the files listed on
+the command line and accessed via the C<< <> >> operator. Since
+C<< <> >> isn't explicitly opened, as a normal filehandle is, an
+L<C<eof()>|/eof FILEHANDLE> before C<< <> >> has been used will cause
+L<C<@ARGV>|perlvar/@ARGV> to be examined to determine if input is
+available. Similarly, an L<C<eof()>|/eof FILEHANDLE> after C<< <> >>
+has returned end-of-file will assume you are processing another
+L<C<@ARGV>|perlvar/@ARGV> list, and if you haven't set
+L<C<@ARGV>|perlvar/@ARGV>, will read input from C<STDIN>; see
+L<perlop/"I/O Operators">.
+
+In a C<< while (<>) >> loop, L<C<eof>|/eof FILEHANDLE> or C<eof(ARGV)>
+can be used to detect the end of each file, whereas
+L<C<eof()>|/eof FILEHANDLE> will detect the end of the very last file
+only. Examples:
# reset line numbering on each input file
while (<>) {
last if eof(); # needed if we're reading from a terminal
}
-Practical hint: you almost never need to use C<eof> in Perl, because the
-input operators typically return C<undef> when they run out of data or
-encounter an error.
+Practical hint: you almost never need to use L<C<eof>|/eof FILEHANDLE>
+in Perl, because the input operators typically return L<C<undef>|/undef
+EXPR> when they run out of data or encounter an error.
=item eval EXPR
X<eval> X<try> X<catch> X<evaluate> X<parse> X<execute>
visible to it, and any package variable settings or subroutine and format
definitions remain afterwards.
-Note that the value is parsed every time the C<eval> executes.
-If EXPR is omitted, evaluates C<$_>. This form is typically used to
-delay parsing and subsequent execution of the text of EXPR until run time.
-
-If the C<unicode_eval> feature is enabled (which is the default under a
-C<use 5.16> or higher declaration), EXPR or C<$_> is treated as a string of
-characters, so C<use utf8> declarations have no effect, and source filters
-are forbidden. In the absence of the C<unicode_eval> feature, the string
-will sometimes be treated as characters and sometimes as bytes, depending
-on the internal encoding, and source filters activated within the C<eval>
-exhibit the erratic, but historical, behaviour of affecting some outer file
-scope that is still compiling. See also the L</evalbytes> keyword, which
-always treats its input as a byte stream and works properly with source
-filters, and the L<feature> pragma.
+Note that the value is parsed every time the L<C<eval>|/eval EXPR>
+executes. If EXPR is omitted, evaluates L<C<$_>|perlvar/$_>. This form
+is typically used to delay parsing and subsequent execution of the text
+of EXPR until run time.
+
+If the
+L<C<"unicode_eval"> feature|feature/The 'unicode_eval' and 'evalbytes' features>
+is enabled (which is the default under a
+C<use 5.16> or higher declaration), EXPR or L<C<$_>|perlvar/$_> is
+treated as a string of characters, so L<C<use utf8>|utf8> declarations
+have no effect, and source filters are forbidden. In the absence of the
+L<C<"unicode_eval"> feature|feature/The 'unicode_eval' and 'evalbytes' features>,
+will sometimes be treated as characters and sometimes as bytes,
+depending on the internal encoding, and source filters activated within
+the L<C<eval>|/eval EXPR> exhibit the erratic, but historical, behaviour
+of affecting some outer file scope that is still compiling. See also
+the L<C<evalbytes>|/evalbytes EXPR> operator, which always treats its
+input as a byte stream and works properly with source filters, and the
+L<feature> pragma.
Problems can arise if the string expands a scalar containing a floating
point number. That scalar can expand to letters, such as C<"NaN"> or
-C<"Infinity">; or, within the scope of a C<use locale>, the decimal
-point character may be something other than a dot (such as a comma).
-None of these are likely to parse as you are likely expecting.
+C<"Infinity">; or, within the scope of a L<C<use locale>|locale>, the
+decimal point character may be something other than a dot (such as a
+comma). None of these are likely to parse as you are likely expecting.
In the second form, the code within the BLOCK is parsed only once--at the
-same time the code surrounding the C<eval> itself was parsed--and executed
+same time the code surrounding the L<C<eval>|/eval EXPR> itself was
+parsed--and executed
within the context of the current Perl program. This form is typically
used to trap exceptions more efficiently than the first (see below), while
also providing the benefit of checking the code within BLOCK at compile
In both forms, the value returned is the value of the last expression
evaluated inside the mini-program; a return statement may be also used, just
as with subroutines. The expression providing the return value is evaluated
-in void, scalar, or list context, depending on the context of the C<eval>
-itself. See L</wantarray> for more on how the evaluation context can be
-determined.
-
-If there is a syntax error or runtime error, or a C<die> statement is
-executed, C<eval> returns C<undef> in scalar context
-or an empty list in list context, and C<$@> is set to the error
-message. (Prior to 5.16, a bug caused C<undef> to be returned
-in list context for syntax errors, but not for runtime errors.)
-If there was no error, C<$@> is set to the empty string. A
-control flow operator like C<last> or C<goto> can bypass the setting of
-C<$@>. Beware that using C<eval> neither silences Perl from printing
-warnings to STDERR, nor does it stuff the text of warning messages into C<$@>.
-To do either of those, you have to use the C<$SIG{__WARN__}> facility, or
-turn off warnings inside the BLOCK or EXPR using S<C<no warnings 'all'>>.
-See L</warn>, L<perlvar>, and L<warnings>.
-
-Note that, because C<eval> traps otherwise-fatal errors, it is useful for
-determining whether a particular feature (such as C<socket> or C<symlink>)
-is implemented. It is also Perl's exception-trapping mechanism, where
-the die operator is used to raise exceptions.
+in void, scalar, or list context, depending on the context of the
+L<C<eval>|/eval EXPR> itself. See L<C<wantarray>|/wantarray> for more
+on how the evaluation context can be determined.
+
+If there is a syntax error or runtime error, or a L<C<die>|/die LIST>
+statement is executed, L<C<eval>|/eval EXPR> returns
+L<C<undef>|/undef EXPR> in scalar context or an empty list in list
+context, and L<C<$@>|perlvar/$@> is set to the error message. (Prior to
+5.16, a bug caused L<C<undef>|/undef EXPR> to be returned in list
+context for syntax errors, but not for runtime errors.) If there was no
+error, L<C<$@>|perlvar/$@> is set to the empty string. A control flow
+operator like L<C<last>|/last LABEL> or L<C<goto>|/goto LABEL> can
+bypass the setting of L<C<$@>|perlvar/$@>. Beware that using
+L<C<eval>|/eval EXPR> neither silences Perl from printing warnings to
+STDERR, nor does it stuff the text of warning messages into
+L<C<$@>|perlvar/$@>. To do either of those, you have to use the
+L<C<$SIG{__WARN__}>|perlvar/%SIG> facility, or turn off warnings inside
+the BLOCK or EXPR using S<C<no warnings 'all'>>. See
+L<C<warn>|/warn LIST>, L<perlvar>, and L<warnings>.
+
+Note that, because L<C<eval>|/eval EXPR> traps otherwise-fatal errors,
+it is useful for determining whether a particular feature (such as
+L<C<socket>|/socket SOCKET,DOMAIN,TYPE,PROTOCOL> or
+L<C<symlink>|/symlink OLDFILE,NEWFILE>) is implemented. It is also
+Perl's exception-trapping mechanism, where the L<C<die>|/die LIST>
+operator is used to raise exceptions.
If you want to trap errors when loading an XS module, some problems with
the binary interface (such as Perl version skew) may be fatal even with
-C<eval> unless C<$ENV{PERL_DL_NONLAZY}> is set. See L<perlrun>.
+L<C<eval>|/eval EXPR> unless C<$ENV{PERL_DL_NONLAZY}> is set. See
+L<perlrun>.
If the code to be executed doesn't vary, you may use the eval-BLOCK
form to trap run-time errors without incurring the penalty of
-recompiling each time. The error, if any, is still returned in C<$@>.
+recompiling each time. The error, if any, is still returned in
+L<C<$@>|perlvar/$@>.
Examples:
# make divide-by-zero nonfatal
# a run-time error
eval '$answer ='; # sets $@
-Using the C<eval{}> form as an exception trap in libraries does have some
+Using the C<eval {}> form as an exception trap in libraries does have some
issues. Due to the current arguably broken state of C<__DIE__> hooks, you
may wish not to trigger any C<__DIE__> hooks that user code may have installed.
You can use the C<local $SIG{__DIE__}> construct for this purpose,
warn $@ if $@;
This is especially significant, given that C<__DIE__> hooks can call
-C<die> again, which has the effect of changing their error messages:
+L<C<die>|/die LIST> again, which has the effect of changing their error
+messages:
# __DIE__ hooks may modify error messages
{
Because this promotes action at a distance, this counterintuitive behavior
may be fixed in a future release.
-With an C<eval>, you should be especially careful to remember what's
-being looked at when:
+With an L<C<eval>|/eval EXPR>, you should be especially careful to
+remember what's being looked at when:
eval $x; # CASE 1
eval "$x"; # CASE 2
particular situation, you can just use symbolic references instead, as
in case 6.
-Before Perl 5.14, the assignment to C<$@> occurred before restoration
+Before Perl 5.14, the assignment to L<C<$@>|perlvar/$@> occurred before
+restoration
of localized variables, which means that for your code to run on older
versions, a temporary is required if you want to mask some but not all
errors:
}
C<eval BLOCK> does I<not> count as a loop, so the loop control statements
-C<next>, C<last>, or C<redo> cannot be used to leave or restart the block.
+L<C<next>|/next LABEL>, L<C<last>|/last LABEL>, or
+L<C<redo>|/redo LABEL> cannot be used to leave or restart the block.
An C<eval ''> executed within a subroutine defined
in the C<DB> package doesn't see the usual
=for Pod::Functions +evalbytes similar to string eval, but intend to parse a bytestream
-This function is like L</eval> with a string argument, except it always
-parses its argument, or C<$_> if EXPR is omitted, as a string of bytes. A
-string containing characters whose ordinal value exceeds 255 results in an
-error. Source filters activated within the evaluated code apply to the
-code itself.
+This function is like L<C<eval>|/eval EXPR> with a string argument,
+except it always parses its argument, or L<C<$_>|perlvar/$_> if EXPR is
+omitted, as a string of bytes. A string containing characters whose
+ordinal value exceeds 255 results in an error. Source filters activated
+within the evaluated code apply to the code itself.
-This function is only available under the C<evalbytes> feature, a
-C<use v5.16> (or higher) declaration, or with a C<CORE::> prefix. See
-L<feature> for more information.
+L<C<evalbytes>|/evalbytes EXPR> is available only if the
+L<C<"evalbytes"> feature|feature/The 'unicode_eval' and 'evalbytes' features>
+is enabled or if it is prefixed with C<CORE::>. The
+L<C<"evalbytes"> feature|feature/The 'unicode_eval' and 'evalbytes' features>
+is enabled automatically with a C<use v5.16> (or higher) declaration in
+the current scope.
=item exec LIST
X<exec> X<execute>
=for Pod::Functions abandon this program to run another
-The C<exec> function executes a system command I<and never returns>;
-use C<system> instead of C<exec> if you want it to return. It fails and
+The L<C<exec>|/exec LIST> function executes a system command I<and never
+returns>; use L<C<system>|/system LIST> instead of L<C<exec>|/exec LIST>
+if you want it to return. It fails and
returns false only if the command does not exist I<and> it is executed
directly instead of via your system's command shell (see below).
-Since it's a common mistake to use C<exec> instead of C<system>, Perl
-warns you if C<exec> is called in void context and if there is a following
-statement that isn't C<die>, C<warn>, or C<exit> (if C<-w> is set--but
-you always do that, right?). If you I<really> want to follow an C<exec>
-with some other statement, you can use one of these styles to avoid the warning:
+Since it's a common mistake to use L<C<exec>|/exec LIST> instead of
+L<C<system>|/system LIST>, Perl warns you if L<C<exec>|/exec LIST> is
+called in void context and if there is a following statement that isn't
+L<C<die>|/die LIST>, L<C<warn>|/warn LIST>, or L<C<exit>|/exit EXPR> (if
+L<warnings> are enabled--but you always do that, right?). If you
+I<really> want to follow an L<C<exec>|/exec LIST> with some other
+statement, you can use one of these styles to avoid the warning:
exec ('foo') or print STDERR "couldn't exec foo: $!";
{ exec ('foo') }; print STDERR "couldn't exec foo: $!";
-If there is more than one argument in LIST, this calls execvp(3) with the
+If there is more than one argument in LIST, this calls L<execvp(3)> with the
arguments in LIST. If there is only one element in LIST, the argument is
checked for shell metacharacters, and if there are any, the entire
argument is passed to the system's command shell for parsing (this is
forces interpretation of the LIST as a multivalued list, even if there
is only a single scalar in the list.) Example:
- $shell = '/bin/csh';
+ my $shell = '/bin/csh';
exec $shell '-sh'; # pretend it's a login shell
or, more directly,
subject to its quirks and capabilities. See L<perlop/"`STRING`">
for details.
-Using an indirect object with C<exec> or C<system> is also more
-secure. This usage (which also works fine with system()) forces
+Using an indirect object with L<C<exec>|/exec LIST> or
+L<C<system>|/system LIST> is also more secure. This usage (which also
+works fine with L<C<system>|/system LIST>) forces
interpretation of the arguments as a multivalued list, even if the
list had just one argument. That way you're safe from the shell
expanding wildcards or splitting up words with whitespace in them.
- @args = ( "echo surprise" );
+ my @args = ( "echo surprise" );
exec @args; # subject to shell escapes
# if @args == 1
The first version, the one without the indirect object, ran the I<echo>
program, passing it C<"surprise"> an argument. The second version didn't;
it tried to run a program named I<"echo surprise">, didn't find it, and set
-C<$?> to a non-zero value indicating failure.
+L<C<$?>|perlvar/$?> to a non-zero value indicating failure.
On Windows, only the C<exec PROGRAM LIST> indirect object syntax will
reliably avoid using the shell; C<exec LIST>, even with more than one
Perl attempts to flush all files opened for output before the exec,
but this may not be supported on some platforms (see L<perlport>).
-To be safe, you may need to set C<$|> ($AUTOFLUSH in English) or
-call the C<autoflush()> method of C<IO::Handle> on any open handles
-to avoid lost output.
+To be safe, you may need to set L<C<$E<verbar>>|perlvar/$E<verbar>>
+(C<$AUTOFLUSH> in L<English>) or call the C<autoflush> method of
+L<C<IO::Handle>|IO::Handle/METHODS> on any open handles to avoid lost
+output.
-Note that C<exec> will not call your C<END> blocks, nor will it invoke
-C<DESTROY> methods on your objects.
+Note that L<C<exec>|/exec LIST> will not call your C<END> blocks, nor
+will it invoke C<DESTROY> methods on your objects.
Portability issues: L<perlport/exec>.
print "True\n" if $hash{$key};
exists may also be called on array elements, but its behavior is much less
-obvious and is strongly tied to the use of L</delete> on arrays.
+obvious and is strongly tied to the use of L<C<delete>|/delete EXPR> on
+arrays.
-B<WARNING:> Calling C<exists> on array values is strongly discouraged. The
+B<WARNING:> Calling L<C<exists>|/exists EXPR> on array values is
+strongly discouraged. The
notion of deleting or checking the existence of Perl array elements is not
conceptually coherent, and can lead to surprising behavior.
Although the most deeply nested array or hash element will not spring into
existence just because its existence was tested, any intervening ones will.
Thus C<< $ref->{"A"} >> and C<< $ref->{"A"}->{"B"} >> will spring
-into existence due to the existence test for the $key element above.
+into existence due to the existence test for the C<$key> element above.
This happens anywhere the arrow operator is used, including even here:
undef $ref;
release.
Use of a subroutine call, rather than a subroutine name, as an argument
-to exists() is an error.
+to L<C<exists>|/exists EXPR> is an error.
exists ⊂ # OK
exists &sub(); # Error
Evaluates EXPR and exits immediately with that value. Example:
- $ans = <STDIN>;
+ my $ans = <STDIN>;
exit 0 if $ans =~ /^[Xx]/;
-See also C<die>. If EXPR is omitted, exits with C<0> status. The only
+See also L<C<die>|/die LIST>. If EXPR is omitted, exits with C<0>
+status. The only
universally recognized values for EXPR are C<0> for success and C<1>
for error; other values are subject to interpretation depending on the
environment in which the Perl program is running. For example, exiting
69 (EX_UNAVAILABLE) from a I<sendmail> incoming-mail filter will cause
the mailer to return the item undelivered, but that's not true everywhere.
-Don't use C<exit> to abort a subroutine if there's any chance that
-someone might want to trap whatever error happened. Use C<die> instead,
-which can be trapped by an C<eval>.
+Don't use L<C<exit>|/exit EXPR> to abort a subroutine if there's any
+chance that someone might want to trap whatever error happened. Use
+L<C<die>|/die LIST> instead, which can be trapped by an
+L<C<eval>|/eval EXPR>.
-The exit() function does not always exit immediately. It calls any
-defined C<END> routines first, but these C<END> routines may not
-themselves abort the exit. Likewise any object destructors that need to
-be called are called before the real exit. C<END> routines and destructors
-can change the exit status by modifying C<$?>. If this is a problem, you
-can call C<POSIX::_exit($status)> to avoid END and destructor processing.
-See L<perlmod> for details.
+The L<C<exit>|/exit EXPR> function does not always exit immediately. It
+calls any defined C<END> routines first, but these C<END> routines may
+not themselves abort the exit. Likewise any object destructors that
+need to be called are called before the real exit. C<END> routines and
+destructors can change the exit status by modifying L<C<$?>|perlvar/$?>.
+If this is a problem, you can call
+L<C<POSIX::_exit($status)>|POSIX/C<_exit>> to avoid C<END> and destructor
+processing. See L<perlmod> for details.
Portability issues: L<perlport/exit>.
And get the correct results.
-Perl only implements the full form of casefolding,
-but you can access the simple folds using L<Unicode::UCD/casefold()> and
-L<Unicode::UCD/prop_invmap()>.
+Perl only implements the full form of casefolding, but you can access
+the simple folds using L<Unicode::UCD/B<casefold()>> and
+L<Unicode::UCD/B<prop_invmap()>>.
For further information on casefolding, refer to
the Unicode Standard, specifically sections 3.13 C<Default Case Operations>,
4.2 C<Case-Normative>, and 5.18 C<Case Mappings>,
available at L<http://www.unicode.org/versions/latest/>, as well as the
Case Charts available at L<http://www.unicode.org/charts/case/>.
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
-This function behaves the same way under various pragma, such as within
-S<C<"use feature 'unicode_strings">>, as L</lc> does, with the single
-exception of C<fc> of LATIN CAPITAL LETTER SHARP S (U+1E9E) within the
-scope of S<C<use locale>>. The foldcase of this character would
-normally be C<"ss">, but as explained in the L</lc> section, case
+This function behaves the same way under various pragmas, such as within
+L<S<C<"use feature 'unicode_strings">>|feature/The 'unicode_strings' feature>,
+as L<C<lc>|/lc EXPR> does, with the single exception of
+L<C<fc>|/fc EXPR> of I<LATIN CAPITAL LETTER SHARP S> (U+1E9E) within the
+scope of L<S<C<use locale>>|locale>. The foldcase of this character
+would normally be C<"ss">, but as explained in the L<C<lc>|/lc EXPR>
+section, case
changes that cross the 255/256 boundary are problematic under locales,
and are hence prohibited. Therefore, this function under locale returns
-instead the string C<"\x{17F}\x{17F}">, which is the LATIN SMALL LETTER
-LONG S. Since that character itself folds to C<"s">, the string of two
+instead the string C<"\x{17F}\x{17F}">, which is the I<LATIN SMALL LETTER
+LONG S>. Since that character itself folds to C<"s">, the string of two
of them together should be equivalent to a single U+1E9E when foldcased.
While the Unicode Standard defines two additional forms of casefolding,
one for Turkic languages and one that never maps one character into multiple
-characters, these are not provided by the Perl core; However, the CPAN module
-C<Unicode::Casing> may be used to provide an implementation.
+characters, these are not provided by the Perl core. However, the CPAN module
+L<C<Unicode::Casing>|Unicode::Casing> may be used to provide an implementation.
-This keyword is available only when the C<"fc"> feature is enabled,
-or when prefixed with C<CORE::>; See L<feature>. Alternately,
-include a C<use v5.16> or later to the current scope.
+L<C<fc>|/fc EXPR> is available only if the
+L<C<"fc"> feature|feature/The 'fc' feature> is enabled or if it is
+prefixed with C<CORE::>. The
+L<C<"fc"> feature|feature/The 'fc' feature> is enabled automatically
+with a C<use v5.16> (or higher) declaration in the current scope.
=item fcntl FILEHANDLE,FUNCTION,SCALAR
X<fcntl>
=for Pod::Functions file control system call
-Implements the fcntl(2) function. You'll probably have to say
+Implements the L<fcntl(2)> function. You'll probably have to say
use Fcntl;
first to get the correct constant definitions. Argument processing and
-value returned work just like C<ioctl> below.
-For example:
+value returned work just like L<C<ioctl>|/ioctl
+FILEHANDLE,FUNCTION,SCALAR> below. For example:
use Fcntl;
- fcntl($filehandle, F_GETFL, $packed_return_buffer)
- or die "can't fcntl F_GETFL: $!";
-
-You don't have to check for C<defined> on the return from C<fcntl>.
-Like C<ioctl>, it maps a C<0> return from the system call into
-C<"0 but true"> in Perl. This string is true in boolean context and C<0>
-in numeric context. It is also exempt from the normal B<-w> warnings
-on improper numeric conversions.
-
-Note that C<fcntl> raises an exception if used on a machine that
-doesn't implement fcntl(2). See the Fcntl module or your fcntl(2)
-manpage to learn what functions are available on your system.
-
-Here's an example of setting a filehandle named C<REMOTE> to be
-non-blocking at the system level. You'll have to negotiate C<$|>
-on your own, though.
+ my $flags = fcntl($filehandle, F_GETFL, 0)
+ or die "Can't fcntl F_GETFL: $!";
+
+You don't have to check for L<C<defined>|/defined EXPR> on the return
+from L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR>. Like
+L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>, it maps a C<0> return
+from the system call into C<"0 but true"> in Perl. This string is true
+in boolean context and C<0> in numeric context. It is also exempt from
+the normal
+L<C<Argument "..." isn't numeric>|perldiag/Argument "%s" isn't numeric%s>
+L<warnings> on improper numeric conversions.
+
+Note that L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR> raises an
+exception if used on a machine that doesn't implement L<fcntl(2)>. See
+the L<Fcntl> module or your L<fcntl(2)> manpage to learn what functions
+are available on your system.
+
+Here's an example of setting a filehandle named C<$REMOTE> to be
+non-blocking at the system level. You'll have to negotiate
+L<C<$E<verbar>>|perlvar/$E<verbar>> on your own, though.
use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);
- $flags = fcntl(REMOTE, F_GETFL, 0)
- or die "Can't get flags for the socket: $!\n";
+ my $flags = fcntl($REMOTE, F_GETFL, 0)
+ or die "Can't get flags for the socket: $!\n";
- $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
- or die "Can't set flags for the socket: $!\n";
+ fcntl($REMOTE, F_SETFL, $flags | O_NONBLOCK)
+ or die "Can't set flags for the socket: $!\n";
Portability issues: L<perlport/fcntl>.
Returns the file descriptor for a filehandle, or undefined if the
filehandle is not open. If there is no real file descriptor at the OS
level, as can happen with filehandles connected to memory objects via
-C<open> with a reference for the third argument, -1 is returned.
+L<C<open>|/open FILEHANDLE,EXPR> with a reference for the third
+argument, -1 is returned.
-This is mainly useful for constructing
-bitmaps for C<select> and low-level POSIX tty-handling operations.
+This is mainly useful for constructing bitmaps for
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT> and low-level POSIX
+tty-handling operations.
If FILEHANDLE is an expression, the value is taken as an indirect
filehandle, generally its name.
You can use this to find out whether two handles refer to the
same underlying descriptor:
- if (fileno(THIS) != -1 && fileno(THIS) == fileno(THAT)) {
- print "THIS and THAT are dups\n";
- } elsif (fileno(THIS) != -1 && fileno(THAT) != -1) {
- print "THIS and THAT have different " .
+ if (fileno($this) != -1 && fileno($this) == fileno($that)) {
+ print "\$this and \$that are dups\n";
+ } elsif (fileno($this) != -1 && fileno($that) != -1) {
+ print "\$this and \$that have different " .
"underlying file descriptors\n";
} else {
- print "At least one of THIS and THAT does " .
+ print "At least one of \$this and \$that does " .
"not have a real file descriptor\n";
}
+The behavior of L<C<fileno>|/fileno FILEHANDLE> on a directory handle
+depends on the operating system. On a system with L<dirfd(3)> or
+similar, L<C<fileno>|/fileno FILEHANDLE> on a directory
+handle returns the underlying file descriptor associated with the
+handle; on systems with no such support, it returns the undefined value,
+and sets L<C<$!>|perlvar/$!> (errno).
+
=item flock FILEHANDLE,OPERATION
X<flock> X<lock> X<locking>
=for Pod::Functions lock an entire file with an advisory lock
-Calls flock(2), or an emulation of it, on FILEHANDLE. Returns true
+Calls L<flock(2)>, or an emulation of it, on FILEHANDLE. Returns true
for success, false on failure. Produces a fatal error if used on a
-machine that doesn't implement flock(2), fcntl(2) locking, or lockf(3).
-C<flock> is Perl's portable file-locking interface, although it locks
-entire files only, not records.
+machine that doesn't implement L<flock(2)>, L<fcntl(2)> locking, or
+L<lockf(3)>. L<C<flock>|/flock FILEHANDLE,OPERATION> is Perl's portable
+file-locking interface, although it locks entire files only, not
+records.
-Two potentially non-obvious but traditional C<flock> semantics are
+Two potentially non-obvious but traditional L<C<flock>|/flock
+FILEHANDLE,OPERATION> semantics are
that it waits indefinitely until the lock is granted, and that its locks
are B<merely advisory>. Such discretionary locks are more flexible, but
offer fewer guarantees. This means that programs that do not also use
-C<flock> may modify files locked with C<flock>. See L<perlport>,
+L<C<flock>|/flock FILEHANDLE,OPERATION> may modify files locked with
+L<C<flock>|/flock FILEHANDLE,OPERATION>. See L<perlport>,
your port's specific documentation, and your system-specific local manpages
for details. It's best to assume traditional behavior if you're writing
portable programs. (But if you're not, you should as always feel perfectly
either individually, or as a group using the C<:flock> tag. LOCK_SH
requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN
releases a previously requested lock. If LOCK_NB is bitwise-or'ed with
-LOCK_SH or LOCK_EX, then C<flock> returns immediately rather than blocking
-waiting for the lock; check the return status to see if you got it.
+LOCK_SH or LOCK_EX, then L<C<flock>|/flock FILEHANDLE,OPERATION> returns
+immediately rather than blocking waiting for the lock; check the return
+status to see if you got it.
To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE
before locking or unlocking it.
-Note that the emulation built with lockf(3) doesn't provide shared
+Note that the emulation built with L<lockf(3)> doesn't provide shared
locks, and it requires that FILEHANDLE be open with write intent. These
-are the semantics that lockf(3) implements. Most if not all systems
-implement lockf(3) in terms of fcntl(2) locking, though, so the
+are the semantics that L<lockf(3)> implements. Most if not all systems
+implement L<lockf(3)> in terms of L<fcntl(2)> locking, though, so the
differing semantics shouldn't bite too many people.
-Note that the fcntl(2) emulation of flock(3) requires that FILEHANDLE
+Note that the L<fcntl(2)> emulation of L<flock(3)> requires that FILEHANDLE
be open with read intent to use LOCK_SH and requires that it be open
with write intent to use LOCK_EX.
-Note also that some versions of C<flock> cannot lock things over the
-network; you would need to use the more system-specific C<fcntl> for
-that. If you like you can force Perl to ignore your system's flock(2)
-function, and so provide its own fcntl(2)-based emulation, by passing
+Note also that some versions of L<C<flock>|/flock FILEHANDLE,OPERATION>
+cannot lock things over the network; you would need to use the more
+system-specific L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR> for
+that. If you like you can force Perl to ignore your system's L<flock(2)>
+function, and so provide its own L<fcntl(2)>-based emulation, by passing
the switch C<-Ud_flock> to the F<Configure> program when you configure
and build a new Perl.
print $mbox $msg,"\n\n";
unlock($mbox);
-On systems that support a real flock(2), locks are inherited across fork()
-calls, whereas those that must resort to the more capricious fcntl(2)
-function lose their locks, making it seriously harder to write servers.
+On systems that support a real L<flock(2)>, locks are inherited across
+L<C<fork>|/fork> calls, whereas those that must resort to the more
+capricious L<fcntl(2)> function lose their locks, making it seriously
+harder to write servers.
-See also L<DB_File> for other flock() examples.
+See also L<DB_File> for other L<C<flock>|/flock FILEHANDLE,OPERATION>
+examples.
Portability issues: L<perlport/flock>.
=for Pod::Functions create a new process just like this one
-Does a fork(2) system call to create a new process running the
+Does a L<fork(2)> system call to create a new process running the
same program at the same point. It returns the child pid to the
-parent process, C<0> to the child process, or C<undef> if the fork is
+parent process, C<0> to the child process, or L<C<undef>|/undef EXPR> if
+the fork is
unsuccessful. File descriptors (and sometimes locks on those descriptors)
are shared, while everything else is copied. On most systems supporting
-fork(), great care has gone into making it extremely efficient (for
+L<fork(2)>, great care has gone into making it extremely efficient (for
example, using copy-on-write technology on data pages), making it the
dominant paradigm for multitasking over the last few decades.
-Perl attempts to flush all files opened for
-output before forking the child process, but this may not be supported
-on some platforms (see L<perlport>). To be safe, you may need to set
-C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method of
-C<IO::Handle> on any open handles to avoid duplicate output.
+Perl attempts to flush all files opened for output before forking the
+child process, but this may not be supported on some platforms (see
+L<perlport>). To be safe, you may need to set
+L<C<$E<verbar>>|perlvar/$E<verbar>> (C<$AUTOFLUSH> in L<English>) or
+call the C<autoflush> method of L<C<IO::Handle>|IO::Handle/METHODS> on
+any open handles to avoid duplicate output.
-If you C<fork> without ever waiting on your children, you will
+If you L<C<fork>|/fork> without ever waiting on your children, you will
accumulate zombies. On some systems, you can avoid this by setting
-C<$SIG{CHLD}> to C<"IGNORE">. See also L<perlipc> for more examples of
-forking and reaping moribund children.
+L<C<$SIG{CHLD}>|perlvar/%SIG> to C<"IGNORE">. See also L<perlipc> for
+more examples of forking and reaping moribund children.
Note that if your forked child inherits system file descriptors like
STDIN and STDOUT that are actually connected by a pipe or socket, even
backgrounded job launched from a remote shell) won't think you're done.
You should reopen those to F</dev/null> if it's any issue.
-On some platforms such as Windows, where the fork() system call is not available,
-Perl can be built to emulate fork() in the Perl interpreter.
-The emulation is designed, at the level of the Perl program,
-to be as compatible as possible with the "Unix" fork().
-However it has limitations that have to be considered in code intended to be portable.
-See L<perlfork> for more details.
+On some platforms such as Windows, where the L<fork(2)> system call is
+not available, Perl can be built to emulate L<C<fork>|/fork> in the Perl
+interpreter. The emulation is designed, at the level of the Perl
+program, to be as compatible as possible with the "Unix" L<fork(2)>.
+However it has limitations that have to be considered in code intended
+
to be portable. See L<perlfork> for more details.
Portability issues: L<perlport/fork>.
=for Pod::Functions declare a picture format with use by the write() function
-Declare a picture format for use by the C<write> function. For
-example:
+Declare a picture format for use by the L<C<write>|/write FILEHANDLE>
+function. For example:
format Something =
Test: @<<<<<<<< @||||| @>>>>>
=for Pod::Functions internal function used for formats
-This is an internal function used by C<format>s, though you may call it,
-too. It formats (see L<perlform>) a list of values according to the
-contents of PICTURE, placing the output into the format output
-accumulator, C<$^A> (or C<$ACCUMULATOR> in English).
-Eventually, when a C<write> is done, the contents of
-C<$^A> are written to some filehandle. You could also read C<$^A>
-and then set C<$^A> back to C<"">. Note that a format typically
-does one C<formline> per line of form, but the C<formline> function itself
-doesn't care how many newlines are embedded in the PICTURE. This means
-that the C<~> and C<~~> tokens treat the entire PICTURE as a single line.
-You may therefore need to use multiple formlines to implement a single
-record format, just like the C<format> compiler.
+This is an internal function used by L<C<format>|/format>s, though you
+may call it, too. It formats (see L<perlform>) a list of values
+according to the contents of PICTURE, placing the output into the format
+output accumulator, L<C<$^A>|perlvar/$^A> (or C<$ACCUMULATOR> in
+L<English>). Eventually, when a L<C<write>|/write FILEHANDLE> is done,
+the contents of L<C<$^A>|perlvar/$^A> are written to some filehandle.
+You could also read L<C<$^A>|perlvar/$^A> and then set
+L<C<$^A>|perlvar/$^A> back to C<"">. Note that a format typically does
+one L<C<formline>|/formline PICTURE,LIST> per line of form, but the
+L<C<formline>|/formline PICTURE,LIST> function itself doesn't care how
+many newlines are embedded in the PICTURE. This means that the C<~> and
+C<~~> tokens treat the entire PICTURE as a single line. You may
+therefore need to use multiple formlines to implement a single record
+format, just like the L<C<format>|/format> compiler.
Be careful if you put double quotes around the picture, because an C<@>
character may be taken to mean the beginning of an array name.
-C<formline> always returns true. See L<perlform> for other examples.
+L<C<formline>|/formline PICTURE,LIST> always returns true. See
+L<perlform> for other examples.
-If you are trying to use this instead of C<write> to capture the output,
-you may find it easier to open a filehandle to a scalar
-(C<< open $fh, ">", \$output >>) and write to that instead.
+If you are trying to use this instead of L<C<write>|/write FILEHANDLE>
+to capture the output, you may find it easier to open a filehandle to a
+scalar (C<< open my $fh, ">", \$output >>) and write to that instead.
=item getc FILEHANDLE
X<getc> X<getchar> X<character> X<file, read>
Returns the next character from the input file attached to FILEHANDLE,
or the undefined value at end of file or if there was an error (in
-the latter case C<$!> is set). If FILEHANDLE is omitted, reads from
+the latter case L<C<$!>|perlvar/$!> is set). If FILEHANDLE is omitted,
+reads from
STDIN. This is not particularly efficient. However, it cannot be
used by itself to fetch single characters without waiting for the user
to hit enter. For that, try something more like:
system "stty", '-icanon', 'eol', "\001";
}
- $key = getc(STDIN);
+ my $key = getc(STDIN);
if ($BSD_STYLE) {
system "stty -cbreak </dev/tty >/dev/tty 2>&1";
}
print "\n";
-Determination of whether $BSD_STYLE should be set
-is left as an exercise to the reader.
+Determination of whether C<$BSD_STYLE> should be set is left as an
+exercise to the reader.
-The C<POSIX::getattr> function can do this more portably on
-systems purporting POSIX compliance. See also the C<Term::ReadKey>
-module from your nearest L<CPAN|http://www.cpan.org> site.
+The L<C<POSIX::getattr>|POSIX/C<getattr>> function can do this more
+portably on systems purporting POSIX compliance. See also the
+L<C<Term::ReadKey>|Term::ReadKey> module on CPAN.
=item getlogin
X<getlogin> X<login>
This implements the C library function of the same name, which on most
systems returns the current login from F</etc/utmp>, if any. If it
-returns the empty string, use C<getpwuid>.
+returns the empty string, use L<C<getpwuid>|/getpwuid UID>.
- $login = getlogin || getpwuid($<) || "Kilroy";
+ my $login = getlogin || getpwuid($<) || "Kilroy";
-Do not consider C<getlogin> for authentication: it is not as
-secure as C<getpwuid>.
+Do not consider L<C<getlogin>|/getlogin> for authentication: it is not
+as secure as L<C<getpwuid>|/getpwuid UID>.
Portability issues: L<perlport/getlogin>.
connection.
use Socket;
- $hersockaddr = getpeername(SOCK);
- ($port, $iaddr) = sockaddr_in($hersockaddr);
- $herhostname = gethostbyaddr($iaddr, AF_INET);
- $herstraddr = inet_ntoa($iaddr);
+ my $hersockaddr = getpeername($sock);
+ my ($port, $iaddr) = sockaddr_in($hersockaddr);
+ my $herhostname = gethostbyaddr($iaddr, AF_INET);
+ my $herstraddr = inet_ntoa($iaddr);
=item getpgrp PID
X<getpgrp> X<group>
Returns the current process group for the specified PID. Use
a PID of C<0> to get the current process group for the
current process. Will raise an exception if used on a machine that
-doesn't implement getpgrp(2). If PID is omitted, returns the process
-group of the current process. Note that the POSIX version of C<getpgrp>
-does not accept a PID argument, so only C<PID==0> is truly portable.
+doesn't implement L<getpgrp(2)>. If PID is omitted, returns the process
+group of the current process. Note that the POSIX version of
+L<C<getpgrp>|/getpgrp PID> does not accept a PID argument, so only
+C<PID==0> is truly portable.
Portability issues: L<perlport/getpgrp>.
Returns the current priority for a process, a process group, or a user.
(See L<getpriority(2)>.) Will raise a fatal exception if used on a
-machine that doesn't implement getpriority(2).
+machine that doesn't implement L<getpriority(2)>.
Portability issues: L<perlport/getpriority>.
X<getprotobynumber> X<getservbyport> X<getpwent> X<getgrent> X<gethostent>
X<getnetent> X<getprotoent> X<getservent> X<setpwent> X<setgrent> X<sethostent>
X<setnetent> X<setprotoent> X<setservent> X<endpwent> X<endgrent> X<endhostent>
-X<endnetent> X<endprotoent> X<endservent>
+X<endnetent> X<endprotoent> X<endservent>
=for Pod::Functions get passwd record given user login name
system C library. In list context, the return values from the
various get routines are as follows:
- # 0 1 2 3 4
- ( $name, $passwd, $gid, $members ) = getgr*
- ( $name, $aliases, $addrtype, $net ) = getnet*
- ( $name, $aliases, $port, $proto ) = getserv*
- ( $name, $aliases, $proto ) = getproto*
- ( $name, $aliases, $addrtype, $length, @addrs ) = gethost*
- ( $name, $passwd, $uid, $gid, $quota,
- $comment, $gcos, $dir, $shell, $expire ) = getpw*
- # 5 6 7 8 9
+ # 0 1 2 3 4
+ my ( $name, $passwd, $gid, $members ) = getgr*
+ my ( $name, $aliases, $addrtype, $net ) = getnet*
+ my ( $name, $aliases, $port, $proto ) = getserv*
+ my ( $name, $aliases, $proto ) = getproto*
+ my ( $name, $aliases, $addrtype, $length, @addrs ) = gethost*
+ my ( $name, $passwd, $uid, $gid, $quota,
+ $comment, $gcos, $dir, $shell, $expire ) = getpw*
+ # 5 6 7 8 9
-(If the entry doesn't exist you get an empty list.)
+(If the entry doesn't exist, the return value is a single meaningless true
+value.)
The exact meaning of the $gcos field varies but it usually contains
the real name of the user (as opposed to the login name) and other
lookup by name, in which case you get the other thing, whatever it is.
(If the entry doesn't exist you get the undefined value.) For example:
- $uid = getpwnam($name);
- $name = getpwuid($num);
- $name = getpwent();
- $gid = getgrnam($name);
- $name = getgrgid($num);
- $name = getgrent();
- #etc.
+ my $uid = getpwnam($name);
+ my $name = getpwuid($num);
+ my $name = getpwent();
+ my $gid = getgrnam($name);
+ my $name = getgrgid($num);
+ my $name = getgrent();
+ # etc.
In I<getpw*()> the fields $quota, $comment, and $expire are special
in that they are unsupported on many systems. If the
aging. In some systems the $comment field may be $class. The $expire
field, if present, encodes the expiration period of the account or the
password. For the availability and the exact meaning of these fields
-in your system, please consult getpwnam(3) and your system's
+in your system, please consult L<getpwnam(3)> and your system's
F<pwd.h> file. You can also find out from within Perl what your
$quota and $comment fields mean and whether you have the $expire field
-by using the C<Config> module and the values C<d_pwquota>, C<d_pwage>,
+by using the L<C<Config>|Config> module and the values C<d_pwquota>, C<d_pwage>,
C<d_pwchange>, C<d_pwcomment>, and C<d_pwexpire>. Shadow password
files are supported only if your vendor has implemented them in the
intuitive fashion that calling the regular C library routines gets the
shadow versions if you're running under privilege or if there exists
-the shadow(3) functions as found in System V (this includes Solaris
+the L<shadow(3)> functions as found in System V (this includes Solaris
and Linux). Those systems that implement a proprietary shadow password
facility are unlikely to be supported.
the login names of the members of the group.
For the I<gethost*()> functions, if the C<h_errno> variable is supported in
-C, it will be returned to you via C<$?> if the function call fails. The
+C, it will be returned to you via L<C<$?>|perlvar/$?> if the function
+call fails. The
C<@addrs> value returned by a successful call is a list of raw
addresses returned by the corresponding library call. In the
Internet domain, each address is four bytes long; you can unpack it
by saying something like:
- ($a,$b,$c,$d) = unpack('W4',$addr[0]);
+ my ($w,$x,$y,$z) = unpack('W4',$addr[0]);
The Socket library makes this slightly easier:
use Socket;
- $iaddr = inet_aton("127.1"); # or whatever address
- $name = gethostbyaddr($iaddr, AF_INET);
+ my $iaddr = inet_aton("127.1"); # or whatever address
+ my $name = gethostbyaddr($iaddr, AF_INET);
# or going the other way
- $straddr = inet_ntoa($iaddr);
+ my $straddr = inet_ntoa($iaddr);
In the opposite way, to resolve a hostname to the IP address
you can write this:
use Socket;
- $packed_ip = gethostbyname("www.perl.org");
+ my $packed_ip = gethostbyname("www.perl.org");
+ my $ip_address;
if (defined $packed_ip) {
$ip_address = inet_ntoa($packed_ip);
}
-Make sure C<gethostbyname()> is called in SCALAR context and that
-its return value is checked for definedness.
+Make sure L<C<gethostbyname>|/gethostbyname NAME> is called in SCALAR
+context and that its return value is checked for definedness.
-The C<getprotobynumber> function, even though it only takes one argument,
-has the precedence of a list operator, so beware:
+The L<C<getprotobynumber>|/getprotobynumber NUMBER> function, even
+though it only takes one argument, has the precedence of a list
+operator, so beware:
getprotobynumber $number eq 'icmp' # WRONG
getprotobynumber($number eq 'icmp') # actually means this
getprotobynumber($number) eq 'icmp' # better this way
If you get tired of remembering which element of the return list
-contains which return value, by-name interfaces are provided
-in standard modules: C<File::stat>, C<Net::hostent>, C<Net::netent>,
-C<Net::protoent>, C<Net::servent>, C<Time::gmtime>, C<Time::localtime>,
-and C<User::grent>. These override the normal built-ins, supplying
-versions that return objects with the appropriate names
-for each field. For example:
+contains which return value, by-name interfaces are provided in standard
+modules: L<C<File::stat>|File::stat>, L<C<Net::hostent>|Net::hostent>,
+L<C<Net::netent>|Net::netent>, L<C<Net::protoent>|Net::protoent>,
+L<C<Net::servent>|Net::servent>, L<C<Time::gmtime>|Time::gmtime>,
+L<C<Time::localtime>|Time::localtime>, and
+L<C<User::grent>|User::grent>. These override the normal built-ins,
+supplying versions that return objects with the appropriate names for
+each field. For example:
use File::stat;
use User::pwent;
- $is_his = (stat($filename)->uid == pwent($whoever)->uid);
+ my $is_his = (stat($filename)->uid == pwent($whoever)->uid);
Even though it looks as though they're the same method calls (uid),
they aren't, because a C<File::stat> object is different from
IPs that the connection might have come in on.
use Socket;
- $mysockaddr = getsockname(SOCK);
- ($port, $myaddr) = sockaddr_in($mysockaddr);
+ my $mysockaddr = getsockname($sock);
+ my ($port, $myaddr) = sockaddr_in($mysockaddr);
printf "Connect to %s [%s]\n",
scalar gethostbyaddr($myaddr, AF_INET),
inet_ntoa($myaddr);
Queries the option named OPTNAME associated with SOCKET at a given LEVEL.
Options may exist at multiple protocol levels depending on the socket
type, but at least the uppermost socket level SOL_SOCKET (defined in the
-C<Socket> module) will exist. To query options at another level the
-protocol number of the appropriate protocol controlling the option
-should be supplied. For example, to indicate that an option is to be
-interpreted by the TCP protocol, LEVEL should be set to the protocol
-number of TCP, which you can get using C<getprotobyname>.
+L<C<Socket>|Socket> module) will exist. To query options at another
+level the protocol number of the appropriate protocol controlling the
+option should be supplied. For example, to indicate that an option is
+to be interpreted by the TCP protocol, LEVEL should be set to the
+protocol number of TCP, which you can get using
+L<C<getprotobyname>|/getprotobyname NAME>.
The function returns a packed string representing the requested socket
-option, or C<undef> on error, with the reason for the error placed in
-C<$!>. Just what is in the packed string depends on LEVEL and OPTNAME;
-consult getsockopt(2) for details. A common case is that the option is an
-integer, in which case the result is a packed integer, which you can decode
-using C<unpack> with the C<i> (or C<I>) format.
+option, or L<C<undef>|/undef EXPR> on error, with the reason for the
+error placed in L<C<$!>|perlvar/$!>. Just what is in the packed string
+depends on LEVEL and OPTNAME; consult L<getsockopt(2)> for details. A
+common case is that the option is an integer, in which case the result
+is a packed integer, which you can decode using
+L<C<unpack>|/unpack TEMPLATE,EXPR> with the C<i> (or C<I>) format.
Here's an example to test whether Nagle's algorithm is enabled on a socket:
scalar context, glob iterates through such filename expansions, returning
undef when the list is exhausted. This is the internal function
implementing the C<< <*.c> >> operator, but you can use it directly. If
-EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in
-more detail in L<perlop/"I/O Operators">.
+EXPR is omitted, L<C<$_>|perlvar/$_> is used. The C<< <*.c> >> operator
+
is discussed in more detail in L<perlop/"I/O Operators">.
-Note that C<glob> splits its arguments on whitespace and treats
-each segment as separate pattern. As such, C<glob("*.c *.h")>
+Note that L<C<glob>|/glob EXPR> splits its arguments on whitespace and
+treats
+each segment as separate pattern. As such, C<glob("*.c *.h")>
matches all files with a F<.c> or F<.h> extension. The expression
C<glob(".* *")> matches all files in the current working directory.
If you want to glob filenames that might contain whitespace, you'll
have to use extra quotes around the spacey filename to protect it.
For example, to glob filenames that have an C<e> followed by a space
-followed by an C<f>, use either of:
+followed by an C<f>, use one of:
- @spacies = <"*e f*">;
- @spacies = glob '"*e f*"';
- @spacies = glob q("*e f*");
+ my @spacies = <"*e f*">;
+ my @spacies = glob '"*e f*"';
+ my @spacies = glob q("*e f*");
If you had to get a variable through, you could do this:
- @spacies = glob "'*${var}e f*'";
- @spacies = glob qq("*${var}e f*");
+ my @spacies = glob "'*${var}e f*'";
+ my @spacies = glob qq("*${var}e f*");
If non-empty braces are the only wildcard characters used in the
-C<glob>, no filenames are matched, but potentially many strings
-are returned. For example, this produces nine strings, one for
+L<C<glob>|/glob EXPR>, no filenames are matched, but potentially many
+strings are returned. For example, this produces nine strings, one for
each pairing of fruits and colors:
- @many = glob "{apple,tomato,cherry}={green,yellow,red}";
+ my @many = glob "{apple,tomato,cherry}={green,yellow,red}";
-This operator is implemented using the standard
-C<File::Glob> extension. See L<File::Glob> for details, including
-C<bsd_glob> which does not treat whitespace as a pattern separator.
+This operator is implemented using the standard C<File::Glob> extension.
+See L<File::Glob> for details, including
+L<C<bsd_glob>|File::Glob/C<bsd_glob>>, which does not treat whitespace
+as a pattern separator.
Portability issues: L<perlport/glob>.
=for Pod::Functions convert UNIX time into record or string using Greenwich time
-Works just like L</localtime> but the returned values are
-localized for the standard Greenwich time zone.
+Works just like L<C<localtime>|/localtime EXPR> but the returned values
+are localized for the standard Greenwich time zone.
Note: When called in list context, $isdst, the last value
returned by gmtime, is always C<0>. There is no
The C<goto LABEL> form finds the statement labeled with LABEL and
resumes execution there. It can't be used to get out of a block or
-subroutine given to C<sort>. It can be used to go almost anywhere
-else within the dynamic scope, including out of subroutines, but it's
-usually better to use some other construct such as C<last> or C<die>.
-The author of Perl has never felt the need to use this form of C<goto>
-(in Perl, that is; C is another matter). (The difference is that C
-does not offer named loops combined with loop control. Perl does, and
-this replaces most structured uses of C<goto> in other languages.)
+subroutine given to L<C<sort>|/sort SUBNAME LIST>. It can be used to go
+almost anywhere else within the dynamic scope, including out of
+subroutines, but it's usually better to use some other construct such as
+L<C<last>|/last LABEL> or L<C<die>|/die LIST>. The author of Perl has
+never felt the need to use this form of L<C<goto>|/goto LABEL> (in Perl,
+that is; C is another matter). (The difference is that C does not offer
+named loops combined with loop control. Perl does, and this replaces
+most structured uses of L<C<goto>|/goto LABEL> in other languages.)
The C<goto EXPR> form expects to evaluate C<EXPR> to a code reference or
a label name. If it evaluates to a code reference, it will be handled
tail recursion via C<goto __SUB__>.
If the expression evaluates to a label name, its scope will be resolved
-dynamically. This allows for computed C<goto>s per FORTRAN, but isn't
-necessarily recommended if you're optimizing for maintainability:
+dynamically. This allows for computed L<C<goto>|/goto LABEL>s per
+FORTRAN, but isn't necessarily recommended if you're optimizing for
+maintainability:
goto ("FOO", "BAR", "GLARCH")[$i];
construct that is optimized away.
The C<goto &NAME> form is quite different from the other forms of
-C<goto>. In fact, it isn't a goto in the normal sense at all, and
-doesn't have the stigma associated with other gotos. Instead, it
-exits the current subroutine (losing any changes set by local()) and
-immediately calls in its place the named subroutine using the current
-value of @_. This is used by C<AUTOLOAD> subroutines that wish to
-load another subroutine and then pretend that the other subroutine had
-been called in the first place (except that any modifications to C<@_>
-in the current subroutine are propagated to the other subroutine.)
-After the C<goto>, not even C<caller> will be able to tell that this
-routine was called first.
+L<C<goto>|/goto LABEL>. In fact, it isn't a goto in the normal sense at
+all, and doesn't have the stigma associated with other gotos. Instead,
+it exits the current subroutine (losing any changes set by
+L<C<local>|/local EXPR>) and immediately calls in its place the named
+subroutine using the current value of L<C<@_>|perlvar/@_>. This is used
+by C<AUTOLOAD> subroutines that wish to load another subroutine and then
+pretend that the other subroutine had been called in the first place
+(except that any modifications to L<C<@_>|perlvar/@_> in the current
+subroutine are propagated to the other subroutine.) After the
+L<C<goto>|/goto LABEL>, not even L<C<caller>|/caller EXPR> will be able
+to tell that this routine was called first.
NAME needn't be the name of a subroutine; it can be a scalar variable
containing a code reference or a block that evaluates to a code
=for Pod::Functions locate elements in a list test true against a given criterion
-This is similar in spirit to, but not the same as, grep(1) and its
+This is similar in spirit to, but not the same as, L<grep(1)> and its
relatives. In particular, it is not limited to using regular expressions.
Evaluates the BLOCK or EXPR for each element of LIST (locally setting
-C<$_> to each element) and returns the list value consisting of those
+L<C<$_>|perlvar/$_> to each element) and returns the list value
+consisting of those
elements for which the expression evaluated to true. In scalar
context, returns the number of times the expression was true.
- @foo = grep(!/^#/, @bar); # weed out comments
+ my @foo = grep(!/^#/, @bar); # weed out comments
or equivalently,
- @foo = grep {!/^#/} @bar; # weed out comments
+ my @foo = grep {!/^#/} @bar; # weed out comments
-Note that C<$_> is an alias to the list value, so it can be used to
+Note that L<C<$_>|perlvar/$_> is an alias to the list value, so it can
+be used to
modify the elements of the LIST. While this is useful and supported,
it can cause bizarre results if the elements of LIST are not variables.
Similarly, grep returns aliases into the original list, much as a for
loop's index variable aliases the list elements. That is, modifying an
-element of a list returned by grep (for example, in a C<foreach>, C<map>
-or another C<grep>) actually modifies the element in the original list.
+element of a list returned by grep (for example, in a C<foreach>,
+L<C<map>|/map BLOCK LIST> or another L<C<grep>|/grep BLOCK LIST>)
+actually modifies the element in the original list.
This is usually something to be avoided when writing clear code.
-If C<$_> is lexical in the scope where the C<grep> appears (because it has
-been declared with the deprecated C<my $_> construct)
-then, in addition to being locally aliased to
-the list elements, C<$_> keeps being lexical inside the block; i.e., it
-can't be seen from the outside, avoiding any potential side-effects.
-
-See also L</map> for a list composed of the results of the BLOCK or EXPR.
+See also L<C<map>|/map BLOCK LIST> for a list composed of the results of
+the BLOCK or EXPR.
=item hex EXPR
X<hex> X<hexadecimal>
=item hex
-=for Pod::Functions convert a string to a hexadecimal number
+=for Pod::Functions convert a hexadecimal string to a number
-Interprets EXPR as a hex string and returns the corresponding value.
-(To convert strings that might start with either C<0>, C<0x>, or C<0b>, see
-L</oct>.) If EXPR is omitted, uses C<$_>.
+Interprets EXPR as a hex string and returns the corresponding numeric value.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
print hex '0xAf'; # prints '175'
print hex 'aF'; # same
+ $valid_input =~ /\A(?:0?[xX])?(?:_?[0-9a-fA-F])*\z/
-Hex strings may only represent integers. Strings that would cause
-integer overflow trigger a warning. Leading whitespace is not stripped,
-unlike oct(). To present something as hex, look into L</printf>,
-L</sprintf>, and L</unpack>.
+A hex string consists of hex digits and an optional C<0x> or C<x> prefix.
+Each hex digit may be preceded by a single underscore, which will be ignored.
+Any other character triggers a warning and causes the rest of the string
+to be ignored (even leading whitespace, unlike L<C<oct>|/oct EXPR>).
+Only integers can be represented, and integer overflow triggers a warning.
+
+To convert strings that might start with any of C<0>, C<0x>, or C<0b>,
+see L<C<oct>|/oct EXPR>. To present something as hex, look into
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST>,
+L<C<sprintf>|/sprintf FORMAT, LIST>, and
+L<C<unpack>|/unpack TEMPLATE,EXPR>.
=item import LIST
X<import>
=for Pod::Functions patch a module's namespace into your own
-There is no builtin C<import> function. It is just an ordinary
-method (subroutine) defined (or inherited) by modules that wish to export
-names to another module. The C<use> function calls the C<import> method
-for the package used. See also L</use>, L<perlmod>, and L<Exporter>.
+There is no builtin L<C<import>|/import LIST> function. It is just an
+ordinary method (subroutine) defined (or inherited) by modules that wish
+to export names to another module. The
+L<C<use>|/use Module VERSION LIST> function calls the
+L<C<import>|/import LIST> method for the package used. See also
+L<C<use>|/use Module VERSION LIST>, L<perlmod>, and L<Exporter>.
=item index STR,SUBSTR,POSITION
X<index> X<indexOf> X<InStr>
beginning of the string. POSITION before the beginning of the string
or after its end is treated as if it were the beginning or the end,
respectively. POSITION and the return value are based at zero.
-If the substring is not found, C<index> returns -1.
+If the substring is not found, L<C<index>|/index STR,SUBSTR,POSITION>
+returns -1.
=item int EXPR
X<int> X<integer> X<truncate> X<trunc> X<floor>
=for Pod::Functions get the integer portion of a number
-Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>.
+Returns the integer portion of EXPR. If EXPR is omitted, uses
+L<C<$_>|perlvar/$_>.
You should not use this function for rounding: one because it truncates
towards C<0>, and two because machine representations of floating-point
numbers can sometimes produce counterintuitive results. For example,
C<int(-6.725/0.025)> produces -268 rather than the correct -269; that's
because it's really more like -268.99999999999994315658 instead. Usually,
-the C<sprintf>, C<printf>, or the C<POSIX::floor> and C<POSIX::ceil>
-functions will serve you better than will int().
+the L<C<sprintf>|/sprintf FORMAT, LIST>,
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST>, or the
+L<C<POSIX::floor>|POSIX/C<floor>> and L<C<POSIX::ceil>|POSIX/C<ceil>>
+functions will serve you better than will L<C<int>|/int EXPR>.
=item ioctl FILEHANDLE,FUNCTION,SCALAR
X<ioctl>
=for Pod::Functions system-dependent device control system call
-Implements the ioctl(2) function. You'll probably first have to say
+Implements the L<ioctl(2)> function. You'll probably first have to say
require "sys/ioctl.ph"; # probably in
# $Config{archlib}/sys/ioctl.ph
(There is a Perl script called B<h2ph> that comes with the Perl kit that
may help you in this, but it's nontrivial.) SCALAR will be read and/or
written depending on the FUNCTION; a C pointer to the string value of SCALAR
-will be passed as the third argument of the actual C<ioctl> call. (If SCALAR
+will be passed as the third argument of the actual
+L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR> call. (If SCALAR
has no string value but does have a numeric value, that value will be
passed rather than a pointer to the string value. To guarantee this to be
-true, add a C<0> to the scalar before using it.) The C<pack> and C<unpack>
+true, add a C<0> to the scalar before using it.) The
+L<C<pack>|/pack TEMPLATE,LIST> and L<C<unpack>|/unpack TEMPLATE,EXPR>
functions may be needed to manipulate the values of structures used by
-C<ioctl>.
+L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>.
-The return value of C<ioctl> (and C<fcntl>) is as follows:
+The return value of L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR> (and
+L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR>) is as follows:
if OS returns: then Perl returns:
-1 undefined value
still easily determine the actual value returned by the operating
system:
- $retval = ioctl(...) || -1;
+ my $retval = ioctl(...) || -1;
printf "System returned %d\n", $retval;
-The special string C<"0 but true"> is exempt from B<-w> complaints
-about improper numeric conversions.
+The special string C<"0 but true"> is exempt from
+L<C<Argument "..." isn't numeric>|perldiag/Argument "%s" isn't numeric%s>
+L<warnings> on improper numeric conversions.
Portability issues: L<perlport/ioctl>.
Joins the separate strings of LIST into a single string with fields
separated by the value of EXPR, and returns that new string. Example:
- $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
+ my $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
-Beware that unlike C<split>, C<join> doesn't take a pattern as its
-first argument. Compare L</split>.
+Beware that unlike L<C<split>|/split E<sol>PATTERNE<sol>,EXPR,LIMIT>,
+L<C<join>|/join EXPR,LIST> doesn't take a pattern as its first argument.
+Compare L<C<split>|/split E<sol>PATTERNE<sol>,EXPR,LIMIT>.
=item keys HASH
X<keys> X<key>
=item keys ARRAY
-=item keys EXPR
-
=for Pod::Functions retrieve list of indices from a hash
Called in list context, returns a list consisting of all the keys of the
order is specific to a given hash; the exact same series of operations
on two hashes may result in a different order for each hash. Any insertion
into the hash may change the order, as will any deletion, with the exception
-that the most recent key returned by C<each> or C<keys> may be deleted
-without changing the order. So long as a given hash is unmodified you may
-rely on C<keys>, C<values> and C<each> to repeatedly return the same order
+that the most recent key returned by L<C<each>|/each HASH> or
+L<C<keys>|/keys HASH> may be deleted without changing the order. So
+long as a given hash is unmodified you may rely on
+L<C<keys>|/keys HASH>, L<C<values>|/values HASH> and L<C<each>|/each
+HASH> to repeatedly return the same order
as each other. See L<perlsec/"Algorithmic Complexity Attacks"> for
details on why hash order is randomized. Aside from the guarantees
provided here the exact details of Perl's hash algorithm and the hash
may behave differently to Perl's hashes with respect to changes in order on
insertion and deletion of items.
-As a side effect, calling keys() resets the internal iterator of the HASH or
-ARRAY (see L</each>). In particular, calling keys() in void context resets
-the iterator with no other overhead.
+As a side effect, calling L<C<keys>|/keys HASH> resets the internal
+iterator of the HASH or ARRAY (see L<C<each>|/each HASH>). In
+particular, calling L<C<keys>|/keys HASH> in void context resets the
+iterator with no other overhead.
Here is yet another way to print your environment:
- @keys = keys %ENV;
- @values = values %ENV;
+ my @keys = keys %ENV;
+ my @values = values %ENV;
while (@keys) {
print pop(@keys), '=', pop(@values), "\n";
}
or how about sorted by key:
- foreach $key (sort(keys %ENV)) {
+ foreach my $key (sort(keys %ENV)) {
print $key, '=', $ENV{$key}, "\n";
}
The returned values are copies of the original keys in the hash, so
-modifying them will not affect the original hash. Compare L</values>.
+modifying them will not affect the original hash. Compare
+L<C<values>|/values HASH>.
-To sort a hash by value, you'll need to use a C<sort> function.
-Here's a descending numeric sort of a hash by its values:
+To sort a hash by value, you'll need to use a
+L<C<sort>|/sort SUBNAME LIST> function. Here's a descending numeric
+sort of a hash by its values:
- foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
+ foreach my $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
printf "%4d %s\n", $hash{$key}, $key;
}
-Used as an lvalue, C<keys> allows you to increase the number of hash buckets
+Used as an lvalue, L<C<keys>|/keys HASH> allows you to increase the
+number of hash buckets
allocated for the given hash. This can gain you a measure of efficiency if
you know the hash is going to get big. (This is similar to pre-extending
an array by assigning a larger number to $#array.) If you say
buckets will be retained even if you do C<%hash = ()>, use C<undef
%hash> if you want to free the storage while C<%hash> is still in scope.
You can't shrink the number of buckets allocated for the hash using
-C<keys> in this way (but you needn't worry about doing this by accident,
-as trying has no effect). C<keys @array> in an lvalue context is a syntax
-error.
-
-Starting with Perl 5.14, C<keys> can take a scalar EXPR, which must contain
-a reference to an unblessed hash or array. The argument will be
-dereferenced automatically. This aspect of C<keys> is considered highly
-experimental. The exact behaviour may change in a future version of Perl.
+L<C<keys>|/keys HASH> in this way (but you needn't worry about doing
+this by accident, as trying has no effect). C<keys @array> in an lvalue
+context is a syntax error.
- for (keys $hashref) { ... }
- for (keys $obj->get_arrayref) { ... }
+Starting with Perl 5.14, an experimental feature allowed
+L<C<keys>|/keys HASH> to take a scalar expression. This experiment has
+been deemed unsuccessful, and was removed as of Perl 5.24.
To avoid confusing would-be users of your code who are running earlier
versions of Perl with mysterious syntax errors, put this sort of thing at
a recent vintage:
use 5.012; # so keys/values/each work on arrays
- use 5.014; # so keys/values/each work on scalars (experimental)
-See also C<each>, C<values>, and C<sort>.
+See also L<C<each>|/each HASH>, L<C<values>|/values HASH>, and
+L<C<sort>|/sort SUBNAME LIST>.
=item kill SIGNAL, LIST
as the number of processes actually killed, e.g. where a process group is
killed).
- $cnt = kill 'HUP', $child1, $child2;
+ my $cnt = kill 'HUP', $child1, $child2;
kill 'KILL', @goners;
SIGNAL may be either a signal name (a string) or a signal number. A signal
the same signal may have different numbers in different operating systems.
A list of signal names supported by the current platform can be found in
-C<$Config{sig_name}>, which is provided by the C<Config> module. See L<Config>
-for more details.
+C<$Config{sig_name}>, which is provided by the L<C<Config>|Config>
+module. See L<Config> for more details.
A negative signal name is the same as a negative signal number, killing process
groups instead of processes. For example, C<kill '-KILL', $pgrp> and
means you usually want to use positive not negative signals.
If SIGNAL is either the number 0 or the string C<ZERO> (or C<SIGZERO>),
-no signal is sent to
-
the process, but C<kill> checks whether it's I<possible> to send a signal to it
+no signal is sent to the process, but L<C<kill>|/kill SIGNAL, LIST>
+checks whether it's I<possible> to send a signal to it
(that means, to be brief, that the process is owned by the same user, or we are
the super-user). This is useful to check that a child process is still
alive (even if only as a zombie) and hasn't changed its UID. See
See L<perlipc/"Signals"> for more details.
-On some platforms such as Windows where the fork() system call is not
-available, Perl can be built to emulate fork() at the interpreter level.
+On some platforms such as Windows where the L<fork(2)> system call is not
+available, Perl can be built to emulate L<C<fork>|/fork> at the
+interpreter level.
This emulation has limitations related to kill that have to be considered,
for code running on Windows and in code intended to be portable.
=for Pod::Functions exit a block prematurely
-The C<last> command is like the C<break> statement in C (as used in
+The L<C<last>|/last LABEL> command is like the C<break> statement in C
+(as used in
loops); it immediately exits the loop in question. If the LABEL is
omitted, the command refers to the innermost enclosing
loop. The C<last EXPR> form, available starting in Perl
5.18.0, allows a label name to be computed at run time,
and is otherwise identical to C<last LABEL>. The
-C<continue> block, if any, is not executed:
+L<C<continue>|/continue BLOCK> block, if any, is not executed:
LINE: while (<STDIN>) {
last LINE if /^$/; # exit when done with header
#...
}
-C<last> cannot be used to exit a block that returns a value such as
-C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit
-a grep() or map() operation.
+L<C<last>|/last LABEL> cannot be used to exit a block that returns a
+value such as C<eval {}>, C<sub {}>, or C<do {}>, and should not be used
+to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
+operation.
Note that a block by itself is semantically identical to a loop
-that executes once. Thus C<last> can be used to effect an early
-exit out of such a block.
+that executes once. Thus L<C<last>|/last LABEL> can be used to effect
+an early exit out of such a block.
-See also L</continue> for an illustration of how C<last>, C<next>, and
-C<redo> work.
+See also L<C<continue>|/continue BLOCK> for an illustration of how
+L<C<last>|/last LABEL>, L<C<next>|/next LABEL>, and
+L<C<redo>|/redo LABEL> work.
Unlike most named operators, this has the same precedence as assignment.
It is also exempt from the looks-like-a-function rule, so
C<last ("foo")."bar"> will cause "bar" to be part of the argument to
-C<last>.
+L<C<last>|/last LABEL>.
=item lc EXPR
X<lc> X<lowercase>
Returns a lowercased version of EXPR. This is the internal function
implementing the C<\L> escape in double-quoted strings.
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
What gets returned depends on several factors:
rules for the remaining code points (this last can only happen if
the UTF8 flag is also set). See L<perllocale>.
-Starting in v5.20, Perl wil use full Unicode rules if the locale is
+Starting in v5.20, Perl uses full Unicode rules if the locale is
UTF-8. Otherwise, there is a deficiency in this scheme, which is that
case changes that cross the 255/256
boundary are not well-defined. For example, the lower case of LATIN CAPITAL
itself, because 0xDF may not be LATIN SMALL LETTER SHARP S in the
current locale, and Perl has no way of knowing if that character even
exists in the locale, much less what code point it is. Perl returns
-a result that is above 255 (almost always the input character unchanged,
+a result that is above 255 (almost always the input character unchanged),
for all instances (and there aren't many) where the 255/256 boundary
would otherwise be crossed; and starting in v5.22, it raises a
L<locale|perldiag/Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".> warning.
is the internal function implementing the C<\l> escape in
double-quoted strings.
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
-This function behaves the same way under various pragmata, such as in a locale,
-as L</lc> does.
+This function behaves the same way under various pragmas, such as in a locale,
+as L<C<lc>|/lc EXPR> does.
=item length EXPR
X<length> X<size>
=for Pod::Functions return the number of characters in a string
Returns the length in I<characters> of the value of EXPR. If EXPR is
-omitted, returns the length of C<$_>. If EXPR is undefined, returns
-C<undef>.
+omitted, returns the length of L<C<$_>|perlvar/$_>. If EXPR is
+undefined, returns L<C<undef>|/undef EXPR>.
This function cannot be used on an entire array or hash to find out how
many elements these have. For that, use C<scalar @array> and C<scalar keys
%hash>, respectively.
-Like all Perl character operations, length() normally deals in logical
+Like all Perl character operations, L<C<length>|/length EXPR> normally
+deals in logical
characters, not physical bytes. For how many bytes a string encoded as
UTF-8 would take up, use C<length(Encode::encode_utf8(EXPR))> (you'll have
to C<use Encode> first). See L<Encode> and L<perlunicode>.
=for Pod::Functions register your socket as a server
-Does the same thing that the listen(2) system call does. Returns true if
+Does the same thing that the L<listen(2)> system call does. Returns true if
it succeeded, false otherwise. See the example in
L<perlipc/"Sockets: Client/Server Communication">.
=for Pod::Functions create a temporary value for a global variable (dynamic scoping)
-You really probably want to be using C<my> instead, because C<local> isn't
-what most people think of as "local". See
-L<perlsub/"Private Variables via my()"> for details.
+You really probably want to be using L<C<my>|/my VARLIST> instead,
+because L<C<local>|/local EXPR> isn't what most people think of as
+
"local". See L<perlsub/"Private Variables via my()"> for details.
A local modifies the listed variables to be local to the enclosing
block, file, or eval. If more than one value is listed, the list must
with the time analyzed for the local time zone. Typically used as
follows:
- # 0 1 2 3 4 5 6 7 8
- ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
+ # 0 1 2 3 4 5 6 7 8
+ my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
localtime(time);
All list elements are numeric and come straight out of the C `struct
C<$isdst> is true if the specified time occurs during Daylight Saving
Time, false otherwise.
-If EXPR is omitted, C<localtime()> uses the current time (as returned
-by time(3)).
+If EXPR is omitted, L<C<localtime>|/localtime EXPR> uses the current
+time (as returned by L<C<time>|/time>).
-In scalar context, C<localtime()> returns the ctime(3) value:
+In scalar context, L<C<localtime>|/localtime EXPR> returns the
+L<ctime(3)> value:
- $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994"
+ my $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994"
-The format of this scalar value is B<not> locale-dependent
-but built into Perl. For GMT instead of local
-time use the L</gmtime> builtin. See also the
-C<Time::Local> module (for converting seconds, minutes, hours, and such back to
-the integer value returned by time()), and the L<POSIX> module's strftime(3)
-and mktime(3) functions.
+The format of this scalar value is B<not> locale-dependent but built
+into Perl. For GMT instead of local time use the
+L<C<gmtime>|/gmtime EXPR> builtin. See also the
+L<C<Time::Local>|Time::Local> module (for converting seconds, minutes,
+hours, and such back to the integer value returned by L<C<time>|/time>),
+and the L<POSIX> module's L<C<strftime>|POSIX/C<strftime>> and
+L<C<mktime>|POSIX/C<mktime>> functions.
To get somewhat similar but locale-dependent date strings, set up your
locale environment variables appropriately (please see L<perllocale>) and
try for example:
use POSIX qw(strftime);
- $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
+ my $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
# or for GMT formatted appropriately for your locale:
- $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;
+ my $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;
-Note that the C<%a> and C<%b>, the short forms of the day of the week
+Note that C<%a> and C<%b>, the short forms of the day of the week
and the month of the year, may not necessarily be three characters wide.
The L<Time::gmtime> and L<Time::localtime> modules provide a convenient,
-by-name access mechanism to the gmtime() and localtime() functions,
-respectively.
+by-name access mechanism to the L<C<gmtime>|/gmtime EXPR> and
+L<C<localtime>|/localtime EXPR> functions, respectively.
For a comprehensive date and time representation look at the
L<DateTime> module on CPAN.
The value returned is the scalar itself, if the argument is a scalar, or a
reference, if the argument is a hash, array or subroutine.
-lock() is a "weak keyword" : this means that if you've defined a function
+L<C<lock>|/lock THING> is a "weak keyword"; this means that if you've
+defined a function
by this name (before any calls to it), that function will be called
instead. If you are not under C<use threads::shared> this does nothing.
See L<threads::shared>.
=for Pod::Functions retrieve the natural logarithm for a number
Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted,
-returns the log of C<$_>. To get the
+returns the log of L<C<$_>|perlvar/$_>. To get the
log of another base, use basic algebra:
The base-N log of a number is equal to the natural log of that number
divided by the natural log of N. For example:
return log($n)/log(10);
}
-See also L</exp> for the inverse operation.
+See also L<C<exp>|/exp EXPR> for the inverse operation.
=item lstat FILEHANDLE
X<lstat>
=for Pod::Functions stat a symbolic link
-Does the same thing as the C<stat> function (including setting the
-special C<_> filehandle) but stats a symbolic link instead of the file
-the symbolic link points to. If symbolic links are unimplemented on
-your system, a normal C<stat> is done. For much more detailed
-information, please see the documentation for C<stat>.
+Does the same thing as the L<C<stat>|/stat FILEHANDLE> function
+(including setting the special C<_> filehandle) but stats a symbolic
+link instead of the file the symbolic link points to. If symbolic links
+are unimplemented on your system, a normal L<C<stat>|/stat FILEHANDLE>
+is done. For much more detailed information, please see the
+documentation for L<C<stat>|/stat FILEHANDLE>.
-If EXPR is omitted, stats C<$_>.
+If EXPR is omitted, stats L<C<$_>|perlvar/$_>.
Portability issues: L<perlport/lstat>.
=for Pod::Functions apply a change to a list to get back a new list with the changes
Evaluates the BLOCK or EXPR for each element of LIST (locally setting
-C<$_> to each element) and returns the list value composed of the
+L<C<$_>|perlvar/$_> to each element) and returns the list value composed
+of the
results of each such evaluation. In scalar context, returns the
total number of elements so generated. Evaluates BLOCK or EXPR in
list context, so each element of LIST may produce zero, one, or
more elements in the returned value.
- @chars = map(chr, @numbers);
+ my @chars = map(chr, @numbers);
translates a list of numbers to the corresponding characters.
assigned to a hash such that the elements
become key/value pairs. See L<perldata> for more details.
- %hash = map { get_a_key_for($_) => $_ } @array;
+ my %hash = map { get_a_key_for($_) => $_ } @array;
is just a funny way to write
- %hash = ();
+ my %hash;
foreach (@array) {
$hash{get_a_key_for($_)} = $_;
}
-Note that C<$_> is an alias to the list value, so it can be used to
-modify the elements of the LIST. While this is useful and supported,
-it can cause bizarre results if the elements of LIST are not variables.
-Using a regular C<foreach> loop for this purpose would be clearer in
-most cases. See also L</grep> for an array composed of those items of
-the original list for which the BLOCK or EXPR evaluates to true.
-
-If C<$_> is lexical in the scope where the C<map> appears (because it has
-been declared with the deprecated C<my $_> construct),
-then, in addition to being locally aliased to
-the list elements, C<$_> keeps being lexical inside the block; that is, it
-can't be seen from the outside, avoiding any potential side-effects.
+Note that L<C<$_>|perlvar/$_> is an alias to the list value, so it can
+be used to modify the elements of the LIST. While this is useful and
+supported, it can cause bizarre results if the elements of LIST are not
+variables. Using a regular C<foreach> loop for this purpose would be
+clearer in most cases. See also L<C<grep>|/grep BLOCK LIST> for an
+array composed of those items of the original list for which the BLOCK
+or EXPR evaluates to true.
C<{> starts both hash references and blocks, so C<map { ...> could be either
the start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look
reported close to the C<}>, but you'll need to change something near the C<{>
such as using a unary C<+> or semicolon to give Perl some help:
- %hash = map { "\L$_" => 1 } @array # perl guesses EXPR. wrong
- %hash = map { +"\L$_" => 1 } @array # perl guesses BLOCK. right
- %hash = map {; "\L$_" => 1 } @array # this also works
- %hash = map { ("\L$_" => 1) } @array # as does this
- %hash = map { lc($_) => 1 } @array # and this.
- %hash = map +( lc($_) => 1 ), @array # this is EXPR and works!
+ my %hash = map { "\L$_" => 1 } @array # perl guesses EXPR. wrong
+ my %hash = map { +"\L$_" => 1 } @array # perl guesses BLOCK. right
+ my %hash = map {; "\L$_" => 1 } @array # this also works
+ my %hash = map { ("\L$_" => 1) } @array # as does this
+ my %hash = map { lc($_) => 1 } @array # and this.
+ my %hash = map +( lc($_) => 1 ), @array # this is EXPR and works!
- %hash = map ( lc($_), 1 ), @array # evaluates to (1, @array)
+ my %hash = map ( lc($_), 1 ), @array # evaluates to (1, @array)
or to force an anon hash constructor use C<+{>:
- @hashes = map +{ lc($_) => 1 }, @array # EXPR, so needs
- # comma at end
+ my @hashes = map +{ lc($_) => 1 }, @array # EXPR, so needs
+ # comma at end
to get a list of anonymous hashes each with only one entry apiece.
=for Pod::Functions create a directory
Creates the directory specified by FILENAME, with permissions
-specified by MASK (as modified by C<umask>). If it succeeds it
-returns true; otherwise it returns false and sets C<$!> (errno).
+specified by MASK (as modified by L<C<umask>|/umask EXPR>). If it
+succeeds it returns true; otherwise it returns false and sets
+L<C<$!>|perlvar/$!> (errno).
MASK defaults to 0777 if omitted, and FILENAME defaults
-to C<$_> if omitted.
+to L<C<$_>|perlvar/$_> if omitted.
In general, it is better to create directories with a permissive MASK
-and let the user modify that with their C<umask> than it is to supply
+and let the user modify that with their L<C<umask>|/umask EXPR> than it
+is to supply
a restrictive MASK and give the user no way to be more permissive.
The exceptions to this rule are when the file or directory should be
-kept private (mail files, for instance). The perlfunc(1) entry on
-C<umask> discusses the choice of MASK in more detail.
+kept private (mail files, for instance). The documentation for
+L<C<umask>|/umask EXPR> discusses the choice of MASK in more detail.
Note that according to the POSIX 1003.1-1996 the FILENAME may have any
number of trailing slashes. Some operating and filesystems do not get
everyone happy.
To recursively create a directory structure, look at
-the C<make_path> function of the L<File::Path> module.
+the L<C<make_path>|File::Path/make_path( $dir1, $dir2, .... )> function
+of the L<File::Path> module.
=item msgctl ID,CMD,ARG
X<msgctl>
=for Pod::Functions SysV IPC message control operations
-Calls the System V IPC function msgctl(2). You'll probably have to say
+Calls the System V IPC function L<msgctl(2)>. You'll probably have to say
use IPC::SysV;
first to get the correct constant definitions. If CMD is C<IPC_STAT>,
then ARG must be a variable that will hold the returned C<msqid_ds>
-structure. Returns like C<ioctl>: the undefined value for error,
-C<"0 but true"> for zero, or the actual return value otherwise. See also
-L<perlipc/"SysV IPC"> and the documentation for C<IPC::SysV> and
-C<IPC::Semaphore>.
+structure. Returns like L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>:
+the undefined value for error, C<"0 but true"> for zero, or the actual
+return value otherwise. See also L<perlipc/"SysV IPC"> and the
+documentation for L<C<IPC::SysV>|IPC::SysV> and
+L<C<IPC::Semaphore>|IPC::Semaphore>.
Portability issues: L<perlport/msgctl>.
=for Pod::Functions get SysV IPC message queue
-Calls the System V IPC function msgget(2). Returns the message queue
-id, or C<undef> on error. See also
-L<perlipc/"SysV IPC"> and the documentation for C<IPC::SysV> and
-C<IPC::Msg>.
+Calls the System V IPC function L<msgget(2)>. Returns the message queue
+id, or L<C<undef>|/undef EXPR> on error. See also L<perlipc/"SysV IPC">
+and the documentation for L<C<IPC::SysV>|IPC::SysV> and
+L<C<IPC::Msg>|IPC::Msg>.
Portability issues: L<perlport/msgget>.
SIZE. Note that when a message is received, the message type as a
native long integer will be the first thing in VAR, followed by the
actual message. This packing may be opened with C<unpack("l! a*")>.
-Taints the variable. Returns true if successful, false
+Taints the variable. Returns true if successful, false
on error. See also L<perlipc/"SysV IPC"> and the documentation for
-C<IPC::SysV> and C<IPC::SysV::Msg>.
+L<C<IPC::SysV>|IPC::SysV> and L<C<IPC::Msg>|IPC::Msg>.
Portability issues: L<perlport/msgrcv>.
type, be followed by the length of the actual message, and then finally
the message itself. This kind of packing can be achieved with
C<pack("l! a*", $type, $message)>. Returns true if successful,
-false on error. See also the C<IPC::SysV>
-and C<IPC::SysV::Msg> documentation.
+false on error. See also L<perlipc/"SysV IPC"> and the documentation
+for L<C<IPC::SysV>|IPC::SysV> and L<C<IPC::Msg>|IPC::Msg>.
Portability issues: L<perlport/msgsnd>.
=for Pod::Functions declare and assign a local variable (lexical scoping)
-A C<my> declares the listed variables to be local (lexically) to the
-enclosing block, file, or C<eval>. If more than one variable is listed,
-the list must be placed in parentheses.
+A L<C<my>|/my VARLIST> declares the listed variables to be local
+(lexically) to the enclosing block, file, or L<C<eval>|/eval EXPR>. If
+more than one variable is listed, the list must be placed in
+parentheses.
The exact semantics and interface of TYPE and ATTRS are still
evolving. TYPE may be a bareword, a constant declared
-with C<use constant>, or C<__PACKAGE__>. It is
-currently bound to the use of the C<fields> pragma,
-and attributes are handled using the C<attributes> pragma, or starting
-from Perl 5.8.0 also via the C<Attribute::Handlers> module. See
-L<perlsub/"Private Variables via my()"> for details, and L<fields>,
-L<attributes>, and L<Attribute::Handlers>.
+with L<C<use constant>|constant>, or L<C<__PACKAGE__>|/__PACKAGE__>. It
+is
+currently bound to the use of the L<fields> pragma,
+and attributes are handled using the L<attributes> pragma, or starting
+from Perl 5.8.0 also via the L<Attribute::Handlers> module. See
+L<perlsub/"Private Variables via my()"> for details.
-Note that with a parenthesised list, C<undef> can be used as a dummy
-placeholder, for example to skip assignment of initial values:
+Note that with a parenthesised list, L<C<undef>|/undef EXPR> can be used
+as a dummy placeholder, for example to skip assignment of initial
+values:
my ( undef, $min, $hour ) = localtime;
=for Pod::Functions iterate a block prematurely
-The C<next> command is like the C<continue> statement in C; it starts
-the next iteration of the loop:
+The L<C<next>|/next LABEL> command is like the C<continue> statement in
+C; it starts the next iteration of the loop:
LINE: while (<STDIN>) {
next LINE if /^#/; # discard comments
#...
}
-Note that if there were a C<continue> block on the above, it would get
+Note that if there were a L<C<continue>|/continue BLOCK> block on the
+above, it would get
executed even on discarded lines. If LABEL is omitted, the command
refers to the innermost enclosing loop. The C<next EXPR> form, available
as of Perl 5.18.0, allows a label name to be computed at run time, being
otherwise identical to C<next LABEL>.
-C<next> cannot be used to exit a block which returns a value such as
-C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit
-a grep() or map() operation.
+L<C<next>|/next LABEL> cannot be used to exit a block which returns a
+value such as C<eval {}>, C<sub {}>, or C<do {}>, and should not be used
+to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
+operation.
Note that a block by itself is semantically identical to a loop
-that executes once. Thus C<next> will exit such a block early.
+that executes once. Thus L<C<next>|/next LABEL> will exit such a block
+early.
-See also L</continue> for an illustration of how C<last>, C<next>, and
-C<redo> work.
+See also L<C<continue>|/continue BLOCK> for an illustration of how
+L<C<last>|/last LABEL>, L<C<next>|/next LABEL>, and
+L<C<redo>|/redo LABEL> work.
Unlike most named operators, this has the same precedence as assignment.
It is also exempt from the looks-like-a-function rule, so
C<next ("foo")."bar"> will cause "bar" to be part of the argument to
-C<next>.
+L<C<next>|/next LABEL>.
=item no MODULE VERSION LIST
X<no declarations>
=for Pod::Functions unimport some module symbols or semantics at compile time
-See the C<use> function, of which C<no> is the opposite.
+See the L<C<use>|/use Module VERSION LIST> function, of which
+L<C<no>|/no MODULE VERSION LIST> is the opposite.
=item oct EXPR
X<oct> X<octal> X<hex> X<hexadecimal> X<binary> X<bin>
$val = oct($val) if $val =~ /^0/;
-If EXPR is omitted, uses C<$_>. To go the other way (produce a number
-in octal), use sprintf() or printf():
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>. To go the other way
+(produce a number in octal), use L<C<sprintf>|/sprintf FORMAT, LIST> or
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST>:
- $dec_perms = (stat("filename"))[2] & 07777;
- $oct_perm_str = sprintf "%o", $perms;
+ my $dec_perms = (stat("filename"))[2] & 07777;
+ my $oct_perm_str = sprintf "%o", $perms;
-The oct() function is commonly used when a string such as C<644> needs
-to be converted into a file mode, for example. Although Perl
+The L<C<oct>|/oct EXPR> function is commonly used when a string such as
+C<644> needs
+to be converted into a file mode, for example. Although Perl
automatically converts strings into numbers as needed, this automatic
conversion assumes base 10.
-Leading white space is ignored without warning, as too are any trailing
-non-digits, such as a decimal point (C<oct> only handles non-negative
-integers, not negative integers or floating point).
+Leading white space is ignored without warning, as too are any trailing
+non-digits, such as a decimal point (L<C<oct>|/oct EXPR> only handles
+non-negative integers, not negative integers or floating point).
=item open FILEHANDLE,EXPR
X<open> X<pipe> X<file, open> X<fopen>
Simple examples to open a file for reading:
- open(my $fh, "<", "input.txt")
- or die "cannot open < input.txt: $!";
+ open(my $fh, "<", "input.txt")
+ or die "Can't open < input.txt: $!";
and for writing:
- open(my $fh, ">", "output.txt")
- or die "cannot open > output.txt: $!";
+ open(my $fh, ">", "output.txt")
+ or die "Can't open > output.txt: $!";
-(The following is a comprehensive reference to open(): for a gentler
-introduction you may consider L<perlopentut>.)
+(The following is a comprehensive reference to
+L<C<open>|/open FILEHANDLE,EXPR>: for a gentler introduction you may
+consider L<perlopentut>.)
If FILEHANDLE is an undefined scalar variable (or array or hash element), a
new filehandle is autovivified, meaning that the variable is assigned a
You can put a C<+> in front of the C<< > >> or C<< < >> to
indicate that you want both read and write access to the file; thus
-C<< +< >> is almost always preferred for read/write updates--the
+C<< +< >> is almost always preferred for read/write updates--the
C<< +> >> mode would clobber the file first. You can't usually use
either read-write mode for updating textfiles, since they have
variable-length records. See the B<-i> switch in L<perlrun> for a
better approach. The file is created with permissions of C<0666>
-modified by the process's C<umask> value.
+modified by the process's L<C<umask>|/umask EXPR> value.
-These various prefixes correspond to the fopen(3) modes of C<r>,
+These various prefixes correspond to the L<fopen(3)> modes of C<r>,
C<r+>, C<w>, C<w+>, C<a>, and C<a+>.
In the one- and two-argument forms of the call, the mode and filename
should be concatenated (in that order), preferably separated by white
space. You can--but shouldn't--omit the mode in these forms when that mode
-is C<< < >>. It is always safe to use the two-argument form of C<open> if
-the filename argument is a known literal.
+is C<< < >>. It is safe to use the two-argument form of
+L<C<open>|/open FILEHANDLE,EXPR> if the filename argument is a known literal.
For three or more arguments if MODE is C<|->, the filename is
interpreted as a command to which output is to be piped, and if MODE
output to us. In the two-argument (and one-argument) form, one should
replace dash (C<->) with the command.
See L<perlipc/"Using open() for IPC"> for more examples of this.
-(You are not allowed to C<open> to a command that pipes both in I<and>
-out, but see L<IPC::Open2>, L<IPC::Open3>, and
+(You are not allowed to L<C<open>|/open FILEHANDLE,EXPR> to a command
+that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>, and
L<perlipc/"Bidirectional Communication with Another Process"> for
alternatives.)
In the form of pipe opens taking three or more arguments, if LIST is specified
(extra arguments after the command name) then LIST becomes arguments
to the command invoked if the platform supports it. The meaning of
-C<open> with more than three arguments for non-pipe modes is not yet
-defined, but experimental "layers" may give extra LIST arguments
-meaning.
+L<C<open>|/open FILEHANDLE,EXPR> with more than three arguments for
+non-pipe modes is not yet defined, but experimental "layers" may give
+extra LIST arguments meaning.
-In the two-argument (and one-argument) form, opening C<< <- >>
+In the two-argument (and one-argument) form, opening C<< <- >>
or C<-> opens STDIN and opening C<< >- >> opens STDOUT.
You may (and usually should) use the three-argument form of open to specify
that affect how the input and output are processed (see L<open> and
L<PerlIO> for more details). For example:
- open(my $fh, "<:encoding(UTF-8)", "filename")
- || die "can't open UTF-8 encoded filename: $!";
+ open(my $fh, "<:encoding(UTF-8)", $filename)
+ || die "Can't open UTF-8 encoded $filename: $!";
opens the UTF8-encoded file containing Unicode characters;
see L<perluniintro>. Note that if layers are specified in the
three-argument form, then default layers stored in ${^OPEN} (see L<perlvar>;
-usually set by the B<open> pragma or the switch B<-CioD>) are ignored.
+usually set by the L<open> pragma or the switch C<-CioD>) are ignored.
Those layers will also be ignored if you specifying a colon with no name
following it. In that case the default layer for the operating system
(:raw on Unix, :crlf on Windows) is used.
Open returns nonzero on success, the undefined value otherwise. If
-the C<open> involved a pipe, the return value happens to be the pid of
-the subprocess.
-
-If you're running Perl on a system that distinguishes between text
-files and binary files, then you should check out L</binmode> for tips
-for dealing with this. The key distinction between systems that need
-C<binmode> and those that don't is their text file formats. Systems
-like Unix, Mac OS, and Plan 9, that end lines with a single
-character and encode that character in C as C<"\n"> do not
-need C<binmode>. The rest need it.
-
-When opening a file, it's seldom a good idea to continue
-if the request failed, so C<open> is frequently used with
-C<die>. Even if C<die> won't do what you want (say, in a CGI script,
+the L<C<open>|/open FILEHANDLE,EXPR> involved a pipe, the return value
+happens to be the pid of the subprocess.
+
+On some systems (in general, DOS- and Windows-based systems)
+L<C<binmode>|/binmode FILEHANDLE, LAYER> is necessary when you're not
+working with a text file. For the sake of portability it is a good idea
+always to use it when appropriate, and never to use it when it isn't
+appropriate. Also, people can set their I/O to be by default
+UTF8-encoded Unicode, not bytes.
+
+When opening a file, it's seldom a good idea to continue
+if the request failed, so L<C<open>|/open FILEHANDLE,EXPR> is frequently
+used with L<C<die>|/die LIST>. Even if L<C<die>|/die LIST> won't do
+what you want (say, in a CGI script,
where you want to format a suitable error message (but there are
modules that can help with that problem)) always check
-the return value from opening a file.
+the return value from opening a file.
The filehandle will be closed when its reference count reaches zero.
-If it is a lexically scoped variable declared with C<my>, that usually
+If it is a lexically scoped variable declared with L<C<my>|/my VARLIST>,
+that usually
means the end of the enclosing scope. However, this automatic close
does not check for errors, so it is better to explicitly close
filehandles, especially those used for writing:
An older style is to use a bareword as the filehandle, as
open(FH, "<", "input.txt")
- or die "cannot open < input.txt: $!";
+ or die "Can't open < input.txt: $!";
Then you can use C<FH> as the filehandle, in C<< close FH >> and C<<
<FH> >> and so on. Note that it's a global variable, so this form is
open(ARTICLE) or die "Can't find article $ARTICLE: $!\n";
Here C<$ARTICLE> must be a global (package) scalar variable - not one
-declared with C<my> or C<state>.
+declared with L<C<my>|/my VARLIST> or L<C<state>|/state VARLIST>.
As a special case the three-argument form with a read/write mode and the third
-argument being C<undef>:
+argument being L<C<undef>|/undef EXPR>:
open(my $tmp, "+>", undef) or die ...
opens a filehandle to an anonymous temporary file. Also using C<< +< >>
works for symmetry, but you really should consider writing something
-to the temporary file first. You will need to seek() to do the
-reading.
+to the temporary file first. You will need to
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE> to do the reading.
-Perl is built using PerlIO by default; Unless you've
+Perl is built using PerlIO by default. Unless you've
changed this (such as building Perl with C<Configure -Uuseperlio>), you can
open filehandles directly to Perl scalars via:
- open($fh, ">", \$variable) || ..
+ open(my $fh, ">", \$variable) || ..
To (re)open C<STDOUT> or C<STDERR> as an in-memory file, close it first:
open(STDOUT, ">", \$variable)
or die "Can't open STDOUT: $!";
-General examples:
-
- open(LOG, ">>/usr/spool/news/twitlog"); # (log is reserved)
- # if the open fails, output is discarded
-
- open(my $dbase, "+<", "dbase.mine") # open for update
- or die "Can't open 'dbase.mine' for update: $!";
-
- open(my $dbase, "+<dbase.mine") # ditto
- or die "Can't open 'dbase.mine' for update: $!";
+See L<perliol> for detailed info on PerlIO.
- open(ARTICLE, "-|", "caesar <$article") # decrypt article
- or die "Can't start caesar: $!";
+General examples:
- open(ARTICLE, "caesar <$article |") # ditto
- or die "Can't start caesar: $!";
+ open(my $log, ">>", "/usr/spool/news/twitlog");
+ # if the open fails, output is discarded
- open(EXTRACT, "|sort >Tmp$$") # $$ is our process id
- or die "Can't start sort: $!";
+ open(my $dbase, "+<", "dbase.mine") # open for update
+ or die "Can't open 'dbase.mine' for update: $!";
- # in-memory files
- open(MEMORY, ">", \$var)
- or die "Can't open memory file: $!";
- print MEMORY "foo!\n"; # output will appear in $var
+ open(my $dbase, "+<dbase.mine") # ditto
+ or die "Can't open 'dbase.mine' for update: $!";
- # process argument list of files along with any includes
-
- foreach $file (@ARGV) {
- process($file, "fh00");
- }
+ open(my $article_fh, "-|", "caesar <$article") # decrypt
+ # article
+ or die "Can't start caesar: $!";
- sub process {
- my($filename, $input) = @_;
- $input++; # this is a string increment
- unless (open($input, "<", $filename)) {
- print STDERR "Can't open $filename: $!\n";
- return;
- }
+ open(my $article_fh, "caesar <$article |") # ditto
+ or die "Can't start caesar: $!";
- local $_;
- while (<$input>) { # note use of indirection
- if (/^#include "(.*)"/) {
- process($1, $input);
- next;
- }
- #... # whatever
- }
- }
+ open(my $out_fh, "|-", "sort >Tmp$$") # $$ is our process id
+ or die "Can't start sort: $!";
-See L<perliol> for detailed info on PerlIO.
+ # in-memory files
+ open(my $memory, ">", \$var)
+ or die "Can't open memory file: $!";
+ print $memory "foo!\n"; # output will appear in $var
You may also, in the Bourne shell tradition, specify an EXPR beginning
with C<< >& >>, in which case the rest of the string is interpreted
as the name of a filehandle (or file descriptor, if numeric) to be
-duped (as C<dup(2)>) and opened. You may use C<&> after C<< > >>,
+duped (as in L<dup(2)>) and opened. You may use C<&> after C<< > >>,
C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>.
The mode you specify should match the mode of the original filehandle.
(Duping a filehandle does not take into account any existing contents
print STDERR "stderr 2\n";
If you specify C<< '<&=X' >>, where C<X> is a file descriptor number
-or a filehandle, then Perl will do an equivalent of C's C<fdopen> of
-that file descriptor (and not call C<dup(2)>); this is more
+or a filehandle, then Perl will do an equivalent of C's L<fdopen(3)> of
+that file descriptor (and not call L<dup(2)>); this is more
parsimonious of file descriptors. For example:
# open for input, reusing the fileno of $fd
- open(FILEHANDLE, "<&=$fd")
+ open(my $fh, "<&=", $fd)
or
- open(FILEHANDLE, "<&=", $fd)
+ open(my $fh, "<&=$fd")
or
- # open for append, using the fileno of OLDFH
- open(FH, ">>&=", OLDFH)
-
-or
-
- open(FH, ">>&=OLDFH")
+ # open for append, using the fileno of $oldfh
+ open(my $fh, ">>&=", $oldfh)
Being parsimonious on filehandles is also useful (besides being
parsimonious) for example when something is dependent on file
-descriptors, like for example locking using flock(). If you do just
-C<< open(A, ">>&B") >>, the filehandle A will not have the same file
-descriptor as B, and therefore flock(A) will not flock(B) nor vice
-versa. But with C<< open(A, ">>&=B") >>, the filehandles will share
-the same underlying system file descriptor.
+descriptors, like for example locking using
+L<C<flock>|/flock FILEHANDLE,OPERATION>. If you do just
+C<< open(my $A, ">>&", $B) >>, the filehandle C<$A> will not have the
+same file descriptor as C<$B>, and therefore C<flock($A)> will not
+C<flock($B)> nor vice versa. But with C<< open(my $A, ">>&=", $B) >>,
+the filehandles will share the same underlying system file descriptor.
Note that under Perls older than 5.8.0, Perl uses the standard C library's'
-fdopen() to implement the C<=> functionality. On many Unix systems,
-fdopen() fails when file descriptors exceed a certain value, typically 255.
+L<fdopen(3)> to implement the C<=> functionality. On many Unix systems,
+L<fdopen(3)> fails when file descriptors exceed a certain value, typically 255.
For Perls 5.8.0 and later, PerlIO is (most often) the default.
-You can see whether your Perl was built with PerlIO by running C<perl -V>
-and looking for the C<useperlio=> line. If C<useperlio> is C<define>, you
-have PerlIO; otherwise you don't.
+You can see whether your Perl was built with PerlIO by running
+C<perl -V:useperlio>. If it says C<'define'>, you have PerlIO;
+otherwise you don't.
If you open a pipe on the command C<-> (that is, specify either C<|-> or C<-|>
-with the one- or two-argument forms of C<open>),
-an implicit C<fork> is done, so C<open> returns twice: in the parent
-process it returns the pid
+with the one- or two-argument forms of
+L<C<open>|/open FILEHANDLE,EXPR>), an implicit L<C<fork>|/fork> is done,
+so L<C<open>|/open FILEHANDLE,EXPR> returns twice: in the parent process
+it returns the pid
of the child process, and in the child process it returns (a defined) C<0>.
Use C<defined($pid)> or C<//> to determine whether the open was successful.
For example, use either
- $child_pid = open(FROM_KID, "-|") // die "can't fork: $!";
+ my $child_pid = open(my $from_kid, "-|") // die "Can't fork: $!";
or
- $child_pid = open(TO_KID, "|-") // die "can't fork: $!";
+ my $child_pid = open(my $to_kid, "|-") // die "Can't fork: $!";
-followed by
+followed by
if ($child_pid) {
# am the parent:
- # either write TO_KID or else read FROM_KID
+ # either write $to_kid or else read $from_kid
...
waitpid $child_pid, 0;
} else {
# am the child; use STDIN/STDOUT normally
...
exit;
- }
+ }
The filehandle behaves normally for the parent, but I/O to that
filehandle is piped from/to the STDOUT/STDIN of the child process.
The following blocks are more or less equivalent:
- open(FOO, "|tr '[a-z]' '[A-Z]'");
- open(FOO, "|-", "tr '[a-z]' '[A-Z]'");
- open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';
- open(FOO, "|-", "tr", '[a-z]', '[A-Z]');
+ open(my $fh, "|tr '[a-z]' '[A-Z]'");
+ open(my $fh, "|-", "tr '[a-z]' '[A-Z]'");
+ open(my $fh, "|-") || exec 'tr', '[a-z]', '[A-Z]';
+ open(my $fh, "|-", "tr", '[a-z]', '[A-Z]');
- open(FOO, "cat -n '$file'|");
- open(FOO, "-|", "cat -n '$file'");
- open(FOO, "-|") || exec "cat", "-n", $file;
- open(FOO, "-|", "cat", "-n", $file);
+ open(my $fh, "cat -n '$file'|");
+ open(my $fh, "-|", "cat -n '$file'");
+ open(my $fh, "-|") || exec "cat", "-n", $file;
+ open(my $fh, "-|", "cat", "-n", $file);
The last two examples in each block show the pipe as "list form", which is
not yet supported on all platforms. A good rule of thumb is that if
-your platform has a real C<fork()> (in other words, if your platform is
-Unix, including Linux and MacOS X), you can use the list form. You would
+your platform has a real L<C<fork>|/fork> (in other words, if your platform is
+Unix, including Linux and MacOS X), you can use the list form. You would
want to use the list form of the pipe so you can pass literal arguments
to the command without risk of the shell interpreting any shell metacharacters
in them. However, this also bars you from opening pipes to commands
that intentionally contain shell metacharacters, such as:
- open(FOO, "|cat -n | expand -4 | lpr")
- // die "Can't open pipeline to lpr: $!";
+ open(my $fh, "|cat -n | expand -4 | lpr")
+ || die "Can't open pipeline to lpr: $!";
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
Perl will attempt to flush all files opened for
output before any operation that may do a fork, but this may not be
supported on some platforms (see L<perlport>). To be safe, you may need
-to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method
-of C<IO::Handle> on any open handles.
+to set L<C<$E<verbar>>|perlvar/$E<verbar>> (C<$AUTOFLUSH> in L<English>)
+or call the C<autoflush> method of L<C<IO::Handle>|IO::Handle/METHODS>
+on any open handles.
On systems that support a close-on-exec flag on files, the flag will
be set for the newly opened file descriptor as determined by the value
-of
C<$^F>. See L<perlvar/$^F>.
+of
L<C<$^F>|perlvar/$^F>. See L<perlvar/$^F>.
Closing any piped filehandle causes the parent process to wait for the
-child to finish, then returns the status value in C<$?> and
-C<${^CHILD_ERROR_NATIVE}>.
+child to finish, then returns the status value in L<C<$?>|perlvar/$?> and
+L<C<${^CHILD_ERROR_NATIVE}>|perlvar/${^CHILD_ERROR_NATIVE}>.
-The filename passed to the one- and two-argument forms of open() will
+The filename passed to the one- and two-argument forms of
+L<C<open>|/open FILEHANDLE,EXPR> will
have leading and trailing whitespace deleted and normal
redirection characters honored. This property, known as "magic open",
can often be used to good effect. A user could specify a filename of
F<"rsh cat file |">, or you could change certain filenames as needed:
$filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/;
- open(FH, $filename) or die "Can't open $filename: $!";
+ open(my $fh, $filename) or die "Can't open $filename: $!";
Use the three-argument form to open a file with arbitrary weird characters in it,
- open(FOO, "<", $file)
- || die "can't open < $file: $!";
+ open(my $fh, "<", $file)
+ || die "Can't open $file: $!";
otherwise it's necessary to protect any leading and trailing whitespace:
$file =~ s#^(\s)#./$1#;
- open(FOO, "< $file\0")
- || die "open failed: $!";
+ open(my $fh, "< $file\0")
+ || die "Can't open $file: $!";
(this may not work on some bizarre filesystems). One should
conscientiously choose between the I<magic> and I<three-argument> form
-of open():
+of L<C<open>|/open FILEHANDLE,EXPR>:
- open(IN, $ARGV[0]) || die "can't open $ARGV[0]: $!";
+ open(my $in, $ARGV[0]) || die "Can't open $ARGV[0]: $!";
will allow the user to specify an argument of the form C<"rsh cat file |">,
but will not work on a filename that happens to have a trailing space, while
- open(IN, "<", $ARGV[0])
- || die "can't open < $ARGV[0]: $!";
+ open(my $in, "<", $ARGV[0])
+ || die "Can't open $ARGV[0]: $!";
-will have exactly the opposite restrictions.
+will have exactly the opposite restrictions. (However, some shells
+support the syntax C<< perl your_program.pl <( rsh cat file ) >>, which
+produces a filename that can be opened normally.)
-If you want a "real" C C<open> (see L<open(2)> on your system), then you
-should use the C<sysopen> function, which involves no such magic (but may
-use subtly different filemodes than Perl open(), which is mapped to C
-fopen()). This is another way to protect your filenames from
-interpretation. For example:
+If you want a "real" C L<open(2)>, then you should use the
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> function, which involves
+no such magic (but uses different filemodes than Perl
+L<C<open>|/open FILEHANDLE,EXPR>, which corresponds to C L<fopen(3)>).
+This is another way to protect your filenames from interpretation. For
+example:
use IO::Handle;
- sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
- or die "sysopen $path: $!";
- $oldfh = select(HANDLE); $| = 1; select($oldfh);
- print HANDLE "stuff $$\n";
- seek(HANDLE, 0, 0);
- print "File contains: ", <HANDLE>;
+ sysopen(my $fh, $path, O_RDWR|O_CREAT|O_EXCL)
+ or die "Can't open $path: $!";
+ $fh->autoflush(1);
+ print $fh "stuff $$\n";
+ seek($fh, 0, 0);
+ print "File contains: ", readline($fh);
-See L</seek> for some details about mixing reading and writing.
+See L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE> for some details about
+mixing reading and writing.
Portability issues: L<perlport/open>.
=for Pod::Functions open a directory
-Opens a directory named EXPR for processing by C<readdir>, C<telldir>,
-C<seekdir>, C<rewinddir>, and C<closedir>. Returns true if successful.
+Opens a directory named EXPR for processing by
+L<C<readdir>|/readdir DIRHANDLE>, L<C<telldir>|/telldir DIRHANDLE>,
+L<C<seekdir>|/seekdir DIRHANDLE,POS>,
+L<C<rewinddir>|/rewinddir DIRHANDLE>, and
+L<C<closedir>|/closedir DIRHANDLE>. Returns true if successful.
DIRHANDLE may be an expression whose value can be used as an indirect
dirhandle, usually the real dirhandle name. If DIRHANDLE is an undefined
scalar variable (or array or hash element), the variable is assigned a
reference to a new anonymous dirhandle; that is, it's autovivified.
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
-See the example at C<readdir>.
+See the example at L<C<readdir>|/readdir DIRHANDLE>.
=item ord EXPR
X<ord> X<encoding>
=for Pod::Functions find a character's numeric representation
Returns the numeric value of the first character of EXPR.
-If EXPR is an empty string, returns 0. If EXPR is omitted, uses C<$_>.
+If EXPR is an empty string, returns 0. If EXPR is omitted, uses
+L<C<$_>|perlvar/$_>.
(Note I<character>, not byte.)
-For the reverse, see L</chr>.
+For the reverse, see L<C<chr>|/chr NUMBER>.
See L<perlunicode> for more about Unicode.
=item our VARLIST
=for Pod::Functions +5.6.0 declare and assign a package variable (lexical scoping)
-C<our> makes a lexical alias to a package (i.e. global) variable of the
-same name in the current package for use within the current lexical scope.
+L<C<our>|/our VARLIST> makes a lexical alias to a package (i.e. global)
+variable of the same name in the current package for use within the
+current lexical scope.
-C<our> has the same scoping rules as C<my> or C<state>, meaning that it is
-only valid within a lexical scope. Unlike C<my> and C<state>, which both
-declare new (lexical) variables, C<our> only creates an alias to an
-existing variable: a package variable of the same name.
+L<C<our>|/our VARLIST> has the same scoping rules as
+L<C<my>|/my VARLIST> or L<C<state>|/state VARLIST>, meaning that it is
+only valid within a lexical scope. Unlike L<C<my>|/my VARLIST> and
+L<C<state>|/state VARLIST>, which both declare new (lexical) variables,
+L<C<our>|/our VARLIST> only creates an alias to an existing variable: a
+package variable of the same name.
-This means that when C<use strict 'vars'> is in effect, C<our> lets you use
-a package variable without qualifying it with the package name, but only within
-the lexical scope of the C<our> declaration.
+This means that when C<use strict 'vars'> is in effect, L<C<our>|/our
+VARLIST> lets you use a package variable without qualifying it with the
+package name, but only within the lexical scope of the
+L<C<our>|/our VARLIST> declaration. This applies immediately--even
+within the same statement.
package Foo;
use strict;
print $Foo::foo; # prints 23
+Because the variable becomes legal immediately under C<use strict 'vars'>, so
+long as there is no variable with that name is already in scope, you can then
+reference the package variable again even within the same statement.
+
+ package Foo;
+ use strict;
+
+ my $foo = $foo; # error, undeclared $foo on right-hand side
+ our $foo = $foo; # no errors
+
If more than one variable is listed, the list must be placed
in parentheses.
our($bar, $baz);
-An C<our> declaration declares an alias for a package variable that will be visible
+An L<C<our>|/our VARLIST> declaration declares an alias for a package
+variable that will be visible
across its entire lexical scope, even across package boundaries. The
package in which the variable is entered is determined at the point
of the declaration, not at the point of use. This means the following
package Bar;
print $bar; # prints 20, as it refers to $Foo::bar
-Multiple C<our> declarations with the same name in the same lexical
+Multiple L<C<our>|/our VARLIST> declarations with the same name in the
+same lexical
scope are allowed if they are in different packages. If they happen
to be in the same package, Perl will emit warnings if you have asked
-for them, just like multiple C<my> declarations. Unlike a second
-C<my> declaration, which will bind the name to a fresh variable, a
-second C<our> declaration in the same package, in the same scope, is
-merely redundant.
+for them, just like multiple L<C<my>|/my VARLIST> declarations. Unlike
+a second L<C<my>|/my VARLIST> declaration, which will bind the name to a
+fresh variable, a second L<C<our>|/our VARLIST> declaration in the same
+package, in the same scope, is merely redundant.
use warnings;
package Foo;
our $bar; # emits warning but has no other effect
print $bar; # still prints 30
-An C<our> declaration may also have a list of attributes associated
-with it.
+An L<C<our>|/our VARLIST> declaration may also have a list of attributes
+associated with it.
The exact semantics and interface of TYPE and ATTRS are still
-evolving. TYPE is currently bound to the use of the C<fields> pragma,
-and attributes are handled using the C<attributes> pragma, or, starting
-from Perl 5.8.0, also via the C<Attribute::Handlers> module. See
-L<perlsub/"Private Variables via my()"> for details, and L<fields>,
-L<attributes>, and L<Attribute::Handlers>.
+evolving. TYPE is currently bound to the use of the L<fields> pragma,
+and attributes are handled using the L<attributes> pragma, or, starting
+from Perl 5.8.0, also via the L<Attribute::Handlers> module. See
+L<perlsub/"Private Variables via my()"> for details.
-Note that with a parenthesised list, C<undef> can be used as a dummy
-placeholder, for example to skip assignment of initial values:
+Note that with a parenthesised list, L<C<undef>|/undef EXPR> can be used
+as a dummy placeholder, for example to skip assignment of initial
+values:
our ( undef, $min, $hour ) = localtime;
-C<our> differs from C<use vars>, which allows use of an unqualified name
-I<only> within the affected package, but across scopes.
+L<C<our>|/our VARLIST> differs from L<C<use vars>|vars>, which allows
+use of an unqualified name I<only> within the affected package, but
+across scopes.
=item pack TEMPLATE,LIST
X<pack>
the converted values. Typically, each converted value looks
like its machine-level representation. For example, on 32-bit machines
an integer may be represented by a sequence of 4 bytes, which will in
-Perl be presented as a string that's 4 characters long.
+Perl be presented as a string that's 4 characters long.
See L<perlpacktut> for an introduction to this function.
< sSiIlLqQ Force little-endian byte-order on the type.
jJfFdDpP (The "little end" touches the construct.)
-The C<< > >> and C<< < >> modifiers can also be used on C<()> groups
-to force a particular byte-order on all components in that group,
+The C<< > >> and C<< < >> modifiers can also be used on C<()> groups
+to force a particular byte-order on all components in that group,
including all its subgroups.
=begin comment
The following rules apply:
-=over
+=over
=item *
something else, described below. Supplying a C<*> for the repeat count
instead of a number means to use however many items are left, except for:
-=over
+=over
-=item *
+=item *
C<@>, C<x>, and C<X>, where it is equivalent to C<0>.
-=item *
+=item *
<.>, where it means relative to the start of the string.
-=item *
+=item *
C<u>, where it is equivalent to 1 (or 45, which here is equivalent).
-=back
+=back
One can replace a numeric repeat count with a template letter enclosed in
brackets to use the packed byte length of the bracketed template for the
When used with C<.>, the repeat count determines the starting position to
calculate the value offset as follows:
-=over
+=over
=item *
=back
The repeat count for C<u> is interpreted as the maximal number of bytes
-to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat
+to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat
count should not be more than 65.
=item *
If the input string is longer than needed, remaining characters are ignored.
-A C<*> for the repeat count uses all characters of the input field.
+A C<*> for the repeat count uses all characters of the input field.
On unpacking, bits are converted to a string of C<0>s and C<1>s.
=item *
The C<h> and C<H> formats pack a string that many nybbles (4-bit groups,
representable as hexadecimal digits, C<"0".."9"> C<"a".."f">) long.
-For each such format, pack() generates 4 bits of result.
+For each such format, L<C<pack>|/pack TEMPLATE,LIST> generates 4 bits of result.
With non-alphabetical characters, the result is based on the 4 least-significant
bits of the input character, i.e., on C<ord($char)%16>. In particular,
characters C<"0"> and C<"1"> generate nybbles 0 and 1, as do bytes
C<"\000"> and C<"\001">. For characters C<"a".."f"> and C<"A".."F">, the result
is compatible with the usual hexadecimal digits, so that C<"a"> and
-C<"A"> both generate the nybble C<0xA==10>. Use only these specific hex
+C<"A"> both generate the nybble C<0xA==10>. Use only these specific hex
characters with this format.
-Starting from the beginning of the template to pack(), each pair
+Starting from the beginning of the template to
+L<C<pack>|/pack TEMPLATE,LIST>, each pair
of characters is converted to 1 character of output. With format C<h>, the
first character of the pair determines the least-significant nybble of the
output character; with format C<H>, it determines the most-significant
If the input string is longer than needed, extra characters are ignored.
A C<*> for the repeat count uses all characters of the input field. For
-unpack(), nybbles are converted to a string of hexadecimal digits.
+L<C<unpack>|/unpack TEMPLATE,EXPR>, nybbles are converted to a string of
+hexadecimal digits.
=item *
could potentially get deallocated before you got around to using the packed
result. The C<P> format packs a pointer to a structure of the size indicated
by the length. A null pointer is created if the corresponding value for
-C<p> or C<P> is C<undef>; similarly with unpack(), where a null pointer
-unpacks into C<undef>.
+C<p> or C<P> is L<C<undef>|/undef EXPR>; similarly with
+L<C<unpack>|/unpack TEMPLATE,EXPR>, where a null pointer unpacks into
+L<C<undef>|/undef EXPR>.
If your system has a strange pointer size--meaning a pointer is neither as
big as an int nor as big as a long--it may not be possible to pack or
unpacking has encoded the sizes or repeat counts for some of its fields
within the structure itself as separate fields.
-For C<pack>, you write I<length-item>C</>I<sequence-item>, and the
+For L<C<pack>|/pack TEMPLATE,LIST>, you write
+I<length-item>C</>I<sequence-item>, and the
I<length-item> describes how the length value is packed. Formats likely
to be of most use are integer-packing ones like C<n> for Java strings,
C<w> for ASN.1 or SNMP, and C<N> for Sun XDR.
-For C<pack>, I<sequence-item> may have a repeat count, in which case
+For L<C<pack>|/pack TEMPLATE,LIST>, I<sequence-item> may have a repeat
+count, in which case
the minimum of that and the number of available items is used as the argument
for I<length-item>. If it has no repeat count or uses a '*', the number
of available items is used.
-For C<unpack>, an internal stack of integer arguments unpacked so far is
+For L<C<unpack>|/unpack TEMPLATE,EXPR>, an internal stack of integer
+arguments unpacked so far is
used. You write C</>I<sequence-item> and the repeat count is obtained by
popping off the last element from the stack. The I<sequence-item> must not
have a repeat count.
pack("n/a* w/a","hello,","world") "\000\006hello,\005world"
pack("a/W2", ord("a") .. ord("z")) "2ab"
-The I<length-item> is not returned explicitly from C<unpack>.
+The I<length-item> is not returned explicitly from
+L<C<unpack>|/unpack TEMPLATE,EXPR>.
Supplying a count to the I<length-item> format letter is only useful with
C<A>, C<a>, or C<Z>. Packing with a I<length-item> of C<a> or C<Z> may
may be larger. This is mainly an issue on 64-bit platforms. You can
see whether using C<!> makes any difference this way:
- printf "format s is %d, s! is %d\n",
+ printf "format s is %d, s! is %d\n",
length pack("s"), length pack("s!");
- printf "format l is %d, l! is %d\n",
+ printf "format l is %d, l! is %d\n",
length pack("l"), length pack("l!");
longsize='4';
longlongsize='8';
-or programmatically via the C<Config> module:
+or programmatically via the L<C<Config>|Config> module:
use Config;
print $Config{shortsize}, "\n";
print $Config{longsize}, "\n";
print $Config{longlongsize}, "\n";
-C<$Config{longlongsize}> is undefined on systems without
+C<$Config{longlongsize}> is undefined on systems without
long long support.
=item *
Basically, Intel and VAX CPUs are little-endian, while everybody else,
including Motorola m68k/88k, PPC, Sparc, HP PA, Power, and Cray, are
-big-endian. Alpha and MIPS can be either: Digital/Compaq uses (well, used)
+big-endian. Alpha and MIPS can be either: Digital/Compaq uses (well, used)
them in little-endian mode, but SGI/Cray uses them in big-endian mode.
The names I<big-endian> and I<little-endian> are comic references to the
You can determine your system endianness with this incantation:
- printf("%#02x ", $_) for unpack("W*", pack L=>0x12345678);
+ printf("%#02x ", $_) for unpack("W*", pack L=>0x12345678);
The byteorder on the platform where Perl was built is also available
via L<Config>:
will have C<"ffff">, signifying that static information doesn't work,
one must use runtime probing.
-For portably packed integers, either use the formats C<n>, C<N>, C<v>,
+For portably packed integers, either use the formats C<n>, C<N>, C<v>,
and C<V> or else use the C<< > >> and C<< < >> modifiers described
immediately below. See also L<perlport>.
Portability-wise the best option is probably to keep to the IEEE 754
64-bit doubles, and of agreed-upon endianness. Another possibility
-is the C<"%a">) format of C<printf>.
+is the C<"%a">) format of L<C<printf>|/printf FILEHANDLE FORMAT, LIST>.
=item *
Starting with Perl 5.10.0, integer and floating-point formats, along with
-the C<p> and C<P> formats and C<()> groups, may all be followed by the
+the C<p> and C<P> formats and C<()> groups, may all be followed by the
C<< > >> or C<< < >> endianness modifiers to respectively enforce big-
-or little-endian byte-order. These modifiers are especially useful
-given how C<n>, C<N>, C<v>, and C<V> don't cover signed integers,
+or little-endian byte-order. These modifiers are especially useful
+given how C<n>, C<N>, C<v>, and C<V> don't cover signed integers,
64-bit integers, or floating-point values.
Here are some concerns to keep in mind when using an endianness modifier:
=over
-=item *
+=item *
-Exchanging signed integers between different platforms works only
+Exchanging signed integers between different platforms works only
when all platforms store them in the same format. Most platforms store
signed integers in two's-complement notation, so usually this is not an issue.
-=item *
+=item *
The C<< > >> or C<< < >> modifiers can only be used on floating-point
formats on big- or little-endian machines. Otherwise, attempting to
use them raises an exception.
-=item *
+=item *
Forcing big- or little-endian byte-order on floating-point values for
data exchange can work only if all platforms use the same
but also dangerous if you don't know exactly what you're doing.
It is not a general way to portably store floating-point values.
-=item *
+=item *
When using C<< > >> or C<< < >> on a C<()> group, this affects
all types inside the group that accept byte-order modifiers,
modifiers to force big- or little-endian byte-order on floating-point values.
Because Perl uses doubles (or long doubles, if configured) internally for
-all numeric calculation, converting from double into float and thence
+all numeric calculation, converting from double into float and thence
to double again loses precision, so C<unpack("f", pack("f", $foo)>)
will not in general equal $foo.
=item *
Pack and unpack can operate in two modes: character mode (C<C0> mode) where
-the packed string is processed per character, and UTF-8 mode (C<U0> mode)
+the packed string is processed per character, and UTF-8 byte mode (C<U0> mode)
where the packed string is processed in its UTF-8-encoded Unicode form on
a byte-by-byte basis. Character mode is the default
unless the format string starts with C<U>. You
-can always switch mode mid-format with an explicit
-C<C0> or C<U0> in the format. This mode remains in effect until the next
+can always switch mode mid-format with an explicit
+C<C0> or C<U0> in the format. This mode remains in effect until the next
mode change, or until the end of the C<()> group it (directly) applies to.
-Using C<C0> to get Unicode characters while using C<U0> to get I<non>-Unicode
+Using C<C0> to get Unicode characters while using C<U0> to get I<non>-Unicode
bytes is not necessarily obvious. Probably only the first of these
is what you want:
- $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
+ $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
perl -CS -ne 'printf "%v04X\n", $_ for unpack("C0A*", $_)'
03B1.03C9
- $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
+ $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
perl -CS -ne 'printf "%v02X\n", $_ for unpack("U0A*", $_)'
CE.B1.CF.89
- $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
+ $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
perl -C0 -ne 'printf "%v02X\n", $_ for unpack("C0A*", $_)'
CE.B1.CF.89
- $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
+ $ perl -CS -E 'say "\x{3B1}\x{3C9}"' |
perl -C0 -ne 'printf "%v02X\n", $_ for unpack("U0A*", $_)'
C3.8E.C2.B1.C3.8F.C2.89
Those examples also illustrate that you should not try to use
-C<pack>/C<unpack> as a substitute for the L<Encode> module.
+L<C<pack>|/pack TEMPLATE,LIST>/L<C<unpack>|/unpack TEMPLATE,EXPR> as a
+substitute for the L<Encode> module.
=item *
You must yourself do any alignment or padding by inserting, for example,
-enough C<"x">es while packing. There is no way for pack() and unpack()
-to know where characters are going to or coming from, so they
+enough C<"x">es while packing. There is no way for
+L<C<pack>|/pack TEMPLATE,LIST> and L<C<unpack>|/unpack TEMPLATE,EXPR>
+to know where characters are going to or coming from, so they
handle their output and input as flat sequences of characters.
=item *
A C<()> group is a sub-TEMPLATE enclosed in parentheses. A group may
-take a repeat count either as postfix, or for unpack(), also via the C</>
+take a repeat count either as postfix, or for
+L<C<unpack>|/unpack TEMPLATE,EXPR>, also via the C</>
template character. Within each repetition of a group, positioning with
C<@> starts over at 0. Therefore, the result of
C<x> and C<X> accept the C<!> modifier to act as alignment commands: they
jump forward or back to the closest position aligned at a multiple of C<count>
-characters. For example, to pack() or unpack() a C structure like
+characters. For example, to L<C<pack>|/pack TEMPLATE,LIST> or
+L<C<unpack>|/unpack TEMPLATE,EXPR> a C structure like
struct {
char c; /* one signed, 8-bit character */
- double d;
+ double d;
char cc[2];
}
=item *
-If TEMPLATE requires more arguments than pack() is given, pack()
+If TEMPLATE requires more arguments than L<C<pack>|/pack TEMPLATE,LIST>
+is given, L<C<pack>|/pack TEMPLATE,LIST>
assumes additional C<""> arguments. If TEMPLATE requires fewer arguments
than given, extra arguments are ignored.
$foo = pack('(sl)<', -42, 4711);
# exactly the same
-The same template may generally also be used in unpack().
+The same template may generally also be used in
+L<C<unpack>|/unpack TEMPLATE,EXPR>.
=item package NAMESPACE
given namespace. The scope of the package declaration is either the
supplied code BLOCK or, in the absence of a BLOCK, from the declaration
itself through the end of current scope (the enclosing block, file, or
-C<eval>). That is, the forms without a BLOCK are operative through the end
-of the current scope, just like the C<my>, C<state>, and C<our> operators.
-All unqualified dynamic identifiers in this scope will be in the given
-namespace, except where overridden by another C<package> declaration or
+L<C<eval>|/eval EXPR>). That is, the forms without a BLOCK are
+operative through the end of the current scope, just like the
+L<C<my>|/my VARLIST>, L<C<state>|/state VARLIST>, and
+L<C<our>|/our VARLIST> operators. All unqualified dynamic identifiers
+in this scope will be in the given namespace, except where overridden by
+another L<C<package>|/package NAMESPACE> declaration or
when they're one of the special identifiers that qualify into C<main::>,
like C<STDOUT>, C<ARGV>, C<ENV>, and the punctuation variables.
A package statement affects dynamic variables only, including those
-you've used C<local> on, but I<not> lexically-scoped variables, which are created
-with C<my>, C<state>, or C<our>. Typically it would be the first
-declaration in a file included by C<require> or C<use>. You can switch into a
-package in more than one place, since this only determines which default
+you've used L<C<local>|/local EXPR> on, but I<not> lexically-scoped
+variables, which are created with L<C<my>|/my VARLIST>,
+L<C<state>|/state VARLIST>, or L<C<our>|/our VARLIST>. Typically it
+would be the first declaration in a file included by
+L<C<require>|/require VERSION> or L<C<use>|/use Module VERSION LIST>.
+You can switch into a
+package in more than one place, since this only determines which default
symbol table the compiler uses for the rest of that block. You can refer to
identifiers in other packages than the current one by prefixing the identifier
with the package name and a double colon, as in C<$SomePack::var>
C<$main::sail> (as well as to C<$main'sail>, still seen in ancient
code, mostly from Perl 4).
-If VERSION is provided, C<package> sets the C<$VERSION> variable in the given
+If VERSION is provided, L<C<package>|/package NAMESPACE> sets the
+C<$VERSION> variable in the given
namespace to a L<version> object with the VERSION provided. VERSION must be a
"strict" style version number as defined by the L<version> module: a positive
decimal number (integer or decimal-fraction) without exponentiation or else a
Opens a pair of connected pipes like the corresponding system call.
Note that if you set up a loop of piped processes, deadlock can occur
unless you are very careful. In addition, note that Perl's pipes use
-IO buffering, so you may need to set C<$|> to flush your WRITEHANDLE
-after each command, depending on the application.
+IO buffering, so you may need to set L<C<$E<verbar>>|perlvar/$E<verbar>>
+to flush your WRITEHANDLE after each command, depending on the
+application.
Returns true on success.
for examples of such things.
On systems that support a close-on-exec flag on files, that flag is set
-on all newly opened file descriptors whose C<fileno>s are I<higher> than
-the current value of $^F (by default 2 for C<STDERR>). See L<perlvar/$^F>.
+on all newly opened file descriptors whose
+L<C<fileno>|/fileno FILEHANDLE>s are I<higher> than the current value of
+L<C<$^F>|perlvar/$^F> (by default 2 for C<STDERR>). See L<perlvar/$^F>.
=item pop ARRAY
X<pop> X<stack>
-=item pop EXPR
-
=item pop
=for Pod::Functions remove the last element from an array and return it
Pops and returns the last value of the array, shortening the array by
one element.
-Returns the undefined value if the array is empty, although this may also
-happen at other times. If ARRAY is omitted, pops the C<@ARGV> array in the
-main program, but the C<@_> array in subroutines, just like C<shift>.
-
-Starting with Perl 5.14, C<pop> can take a scalar EXPR, which must hold a
-reference to an unblessed array. The argument will be dereferenced
-automatically. This aspect of C<pop> is considered highly experimental.
-The exact behaviour may change in a future version of Perl.
-
-To avoid confusing would-be users of your code who are running earlier
-versions of Perl with mysterious syntax errors, put this sort of thing at
-the top of your file to signal that your code will work I<only> on Perls of
-a recent vintage:
+Returns the undefined value if the array is empty, although this may
+also happen at other times. If ARRAY is omitted, pops the
+L<C<@ARGV>|perlvar/@ARGV> array in the main program, but the
+L<C<@_>|perlvar/@_> array in subroutines, just like
+L<C<shift>|/shift ARRAY>.
- use 5.014; # so push/pop/etc work on scalars (experimental)
+Starting with Perl 5.14, an experimental feature allowed
+L<C<pop>|/pop ARRAY> to take a
+scalar expression. This experiment has been deemed unsuccessful, and was
+removed as of Perl 5.24.
=item pos SCALAR
X<pos> X<match, position>
=for Pod::Functions find or set the offset for the last/next m//g search
Returns the offset of where the last C<m//g> search left off for the
-variable in question (C<$_> is used when the variable is not
-specified). Note that 0 is a valid match offset. C<undef> indicates
+variable in question (L<C<$_>|perlvar/$_> is used when the variable is not
+specified). This offset is in characters unless the
+(no-longer-recommended) L<C<use bytes>|bytes> pragma is in effect, in
+which case the offset is in bytes. Note that 0 is a valid match offset.
+L<C<undef>|/undef EXPR> indicates
that the search position is reset (usually due to match failure, but
can also be because no match has yet been run on the scalar).
-C<pos> directly accesses the location used by the regexp engine to
-store the offset, so assigning to C<pos> will change that offset, and
-so will also influence the C<\G> zero-width assertion in regular
-expressions. Both of these effects take place for the next match, so
-you can't affect the position with C<pos> during the current match,
-such as in C<(?{pos() = 5})> or C<s//pos() = 5/e>.
+L<C<pos>|/pos SCALAR> directly accesses the location used by the regexp
+engine to store the offset, so assigning to L<C<pos>|/pos SCALAR> will
+change that offset, and so will also influence the C<\G> zero-width
+assertion in regular expressions. Both of these effects take place for
+the next match, so you can't affect the position with
+L<C<pos>|/pos SCALAR> during the current match, such as in
+C<(?{pos() = 5})> or C<s//pos() = 5/e>.
-Setting C<pos> also resets the I<matched with zero-length> flag, described
+Setting L<C<pos>|/pos SCALAR> also resets the I<matched with
+zero-length> flag, described
under L<perlre/"Repeated Patterns Matching a Zero-length Substring">.
Because a failed C<m//gc> match doesn't reset the offset, the return
-from C<pos> won't change either in this case. See L<perlre> and
-L<perlop>.
+from L<C<pos>|/pos SCALAR> won't change either in this case. See
+L<perlre> and L<perlop>.
=item print FILEHANDLE LIST
X<print>
FILEHANDLE is a variable and the next token is a term, it may be
misinterpreted as an operator unless you interpose a C<+> or put
parentheses around the arguments.) If FILEHANDLE is omitted, prints to the
-last selected (see L</select>) output handle. If LIST is omitted, prints
-C<$_> to the currently selected output handle. To use FILEHANDLE alone to
-print the content of C<$_> to it, you must use a real filehandle like
+last selected (see L<C<select>|/select FILEHANDLE>) output handle. If
+LIST is omitted, prints L<C<$_>|perlvar/$_> to the currently selected
+output handle. To use FILEHANDLE alone to print the content of
+L<C<$_>|perlvar/$_> to it, you must use a bareword filehandle like
C<FH>, not an indirect one like C<$fh>. To set the default output handle
to something other than STDOUT, use the select operation.
-The current value of C<$,> (if any) is printed between each LIST item. The
-current value of C<$\> (if any) is printed after the entire LIST has been
-printed. Because print takes a LIST, anything in the LIST is evaluated in
-list context, including any subroutines whose return lists you pass to
-C<print>. Be careful not to follow the print keyword with a left
+The current value of L<C<$,>|perlvar/$,> (if any) is printed between
+each LIST item. The current value of L<C<$\>|perlvar/$\> (if any) is
+printed after the entire LIST has been printed. Because print takes a
+LIST, anything in the LIST is evaluated in list context, including any
+subroutines whose return lists you pass to
+L<C<print>|/print FILEHANDLE LIST>. Be careful not to follow the print
+keyword with a left
parenthesis unless you want the corresponding right parenthesis to
terminate the arguments to the print; put parentheses around all arguments
(or interpose a C<+>, but that doesn't look as good).
=for Pod::Functions output a formatted list to a filehandle
-Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\>
-(the output record separator) is not appended. The FORMAT and the
-LIST are actually parsed as a single list. The first argument
-of the list will be interpreted as the C<printf> format. This
-means that C<printf(@_)> will use C<$_[0]> as the format. See
-L<sprintf|/sprintf FORMAT, LIST> for an
-explanation of the format argument. If C<use locale> for C<LC_NUMERIC>
-Look for this throught pod
-is in effect and
-POSIX::setlocale() has been called, the character used for the decimal
-separator in formatted floating-point numbers is affected by the C<LC_NUMERIC>
-locale setting. See L<perllocale> and L<POSIX>.
-
-For historical reasons, if you omit the list, C<$_> is used as the format;
-to use FILEHANDLE without a list, you must use a real filehandle like
+Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that
+L<C<$\>|perlvar/$\> (the output record separator) is not appended. The
+FORMAT and the LIST are actually parsed as a single list. The first
+argument of the list will be interpreted as the
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST> format. This means that
+C<printf(@_)> will use C<$_[0]> as the format. See
+L<sprintf|/sprintf FORMAT, LIST> for an explanation of the format
+argument. If C<use locale> (including C<use locale ':not_characters'>)
+is in effect and L<C<POSIX::setlocale>|POSIX/C<setlocale>> has been
+called, the character used for the decimal separator in formatted
+floating-point numbers is affected by the C<LC_NUMERIC> locale setting.
+See L<perllocale> and L<POSIX>.
+
+For historical reasons, if you omit the list, L<C<$_>|perlvar/$_> is
+used as the format;
+to use FILEHANDLE without a list, you must use a bareword filehandle like
C<FH>, not an indirect one like C<$fh>. However, this will rarely do what
-you want; if $_ contains formatting codes, they will be replaced with the
-empty string and a warning will be emitted if warnings are enabled. Just
-use C<print> if you want to print the contents of $_.
+you want; if L<C<$_>|perlvar/$_> contains formatting codes, they will be
+replaced with the empty string and a warning will be emitted if
+L<warnings> are enabled. Just use L<C<print>|/print FILEHANDLE LIST> if
+you want to print the contents of L<C<$_>|perlvar/$_>.
-Don't fall into the trap of using a C<printf> when a simple
-C<print> would do. The C<print> is more efficient and less
-error prone.
+Don't fall into the trap of using a
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST> when a simple
+L<C<print>|/print FILEHANDLE LIST> would do. The
+L<C<print>|/print FILEHANDLE LIST> is more efficient and less error
+prone.
=item prototype FUNCTION
X<prototype>
+=item prototype
+
=for Pod::Functions +5.002 get the prototype (if any) of a subroutine
-Returns the prototype of a function as a string (or C<undef> if the
+Returns the prototype of a function as a string (or
+L<C<undef>|/undef EXPR> if the
function has no prototype). FUNCTION is a reference to, or the name of,
-the function whose prototype you want to retrieve.
+the function whose prototype you want to retrieve. If FUNCTION is omitted,
+L<C<$_>|perlvar/$_> is used.
If FUNCTION is a string starting with C<CORE::>, the rest is taken as a
name for a Perl builtin. If the builtin's arguments
cannot be adequately expressed by a prototype
-(such as C<system>), prototype() returns C<undef>, because the builtin
+(such as L<C<system>|/system LIST>), L<C<prototype>|/prototype FUNCTION>
+returns L<C<undef>|/undef EXPR>, because the builtin
does not really behave like a Perl function. Otherwise, the string
describing the equivalent prototype is returned.
=item push ARRAY,LIST
X<push> X<stack>
-=item push EXPR,LIST
-
=for Pod::Functions append one or more elements to an array
Treats ARRAY as a stack by appending the values of LIST to the end of
ARRAY. The length of ARRAY increases by the length of LIST. Has the same
effect as
- for $value (LIST) {
+ for my $value (LIST) {
$ARRAY[++$#ARRAY] = $value;
}
but is more efficient. Returns the number of elements in the array following
-the completed C<push>.
+the completed L<C<push>|/push ARRAY,LIST>.
-Starting with Perl 5.14, C<push> can take a scalar EXPR, which must hold a
-reference to an unblessed array. The argument will be dereferenced
-automatically. This aspect of C<push> is considered highly experimental.
-The exact behaviour may change in a future version of Perl.
-
-To avoid confusing would-be users of your code who are running earlier
-versions of Perl with mysterious syntax errors, put this sort of thing at
-the top of your file to signal that your code will work I<only> on Perls of
-a recent vintage:
-
- use 5.014; # so push/pop/etc work on scalars (experimental)
+Starting with Perl 5.14, an experimental feature allowed
+L<C<push>|/push ARRAY,LIST> to take a
+scalar expression. This experiment has been deemed unsuccessful, and was
+removed as of Perl 5.24.
=item q/STRING/
the C<\Q> escape in double-quoted strings.
(See below for the behavior on non-ASCII code points.)
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
quotemeta (and C<\Q> ... C<\E>) are useful when interpolating strings into
regular expressions, because by default an interpolated variable will be
$sentence =~ s{$quoted_substring}{big bad wolf};
Will both leave the sentence as is.
-Normally, when accepting literal string
-input from the user, quotemeta() or C<\Q> must be used.
+Normally, when accepting literal string input from the user,
+L<C<quotemeta>|/quotemeta EXPR> or C<\Q> must be used.
In Perl v5.14, all non-ASCII characters are quoted in non-UTF-8-encoded
strings, but not quoted in UTF-8 strings.
unchanged.
Also unchanged is the quoting of non-UTF-8 strings when outside the
-scope of a C<use feature 'unicode_strings'>, which is to quote all
+scope of a
+L<C<use feature 'unicode_strings'>|feature/The 'unicode_strings' feature>,
+which is to quote all
characters in the upper Latin1 range. This provides complete backwards
compatibility for old programs which do not use Unicode. (Note that
C<unicode_strings> is automatically enabled within the scope of a
S<C<use v5.12>> or greater.)
-Within the scope of C<use locale>, all non-ASCII Latin1 code points
+Within the scope of L<C<use locale>|locale>, all non-ASCII Latin1 code
+points
are quoted whether the string is encoded as UTF-8 or not. As mentioned
above, locale does not affect the quoting of ASCII-range characters.
This protects against those locales where characters such as C<"|"> are
omitted, the value C<1> is used. Currently EXPR with the value C<0> is
also special-cased as C<1> (this was undocumented before Perl 5.8.0
and is subject to change in future versions of Perl). Automatically calls
-C<srand> unless C<srand> has already been called. See also C<srand>.
+L<C<srand>|/srand EXPR> unless L<C<srand>|/srand EXPR> has already been
+called. See also L<C<srand>|/srand EXPR>.
-Apply C<int()> to the value returned by C<rand()> if you want random
-integers instead of random fractional numbers. For example,
+Apply L<C<int>|/int EXPR> to the value returned by L<C<rand>|/rand EXPR>
+if you want random integers instead of random fractional numbers. For
+example,
int(rand(10))
large or too small, then your version of Perl was probably compiled
with the wrong number of RANDBITS.)
-B<C<rand()> is not cryptographically secure. You should not rely
+B<L<C<rand>|/rand EXPR> is not cryptographically secure. You should not rely
on it in security-sensitive situations.> As of this writing, a
number of third-party CPAN modules offer random number generators
intended by their authors to be cryptographically secure,
Attempts to read LENGTH I<characters> of data into variable SCALAR
from the specified FILEHANDLE. Returns the number of characters
actually read, C<0> at end of file, or undef if there was an error (in
-the latter case C<$!> is also set). SCALAR will be grown or shrunk
+the latter case L<C<$!>|perlvar/$!> is also set). SCALAR will be grown
+or shrunk
so that the last character actually read is the last character of the
scalar after the read.
bytes before the result of the read is appended.
The call is implemented in terms of either Perl's or your system's native
-fread(3) library function. To get a true read(2) system call, see
+L<fread(3)> library function. To get a true L<read(2)> system call, see
L<sysread|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>.
Note the I<characters>: depending on the status of the filehandle,
either (8-bit) bytes or characters are read. By default, all
filehandles operate on bytes, but for example if the filehandle has
-been opened with the C<:utf8> I/O layer (see L</open>, and the C<open>
-pragma, L<open>), the I/O will operate on UTF8-encoded Unicode
-characters, not bytes. Similarly for the C<:encoding> pragma:
+been opened with the C<:utf8> I/O layer (see
+L<C<open>|/open FILEHANDLE,EXPR>, and the L<open>
+pragma), the I/O will operate on UTF8-encoded Unicode
+characters, not bytes. Similarly for the C<:encoding> layer:
in that case pretty much any characters can be read.
=item readdir DIRHANDLE
=for Pod::Functions get a directory from a directory handle
-Returns the next directory entry for a directory opened by C<opendir>.
+Returns the next directory entry for a directory opened by
+L<C<opendir>|/opendir DIRHANDLE,EXPR>.
If used in list context, returns all the rest of the entries in the
directory. If there are no more entries, returns the undefined value in
scalar context and the empty list in list context.
-If you're planning to filetest the return values out of a C<readdir>, you'd
-better prepend the directory in question. Otherwise, because we didn't
-C<chdir> there, it would have been testing the wrong file.
+If you're planning to filetest the return values out of a
+L<C<readdir>|/readdir DIRHANDLE>, you'd better prepend the directory in
+question. Otherwise, because we didn't L<C<chdir>|/chdir EXPR> there,
+it would have been testing the wrong file.
- opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!";
- @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh);
+ opendir(my $dh, $some_dir) || die "Can't opendir $some_dir: $!";
+ my @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh);
closedir $dh;
-As of Perl 5.12 you can use a bare C<readdir> in a C<while> loop,
-which will set C<$_> on every iteration.
+As of Perl 5.12 you can use a bare L<C<readdir>|/readdir DIRHANDLE> in a
+C<while> loop, which will set L<C<$_>|perlvar/$_> on every iteration.
- opendir(my $dh, $some_dir) || die;
- while(readdir $dh) {
+ opendir(my $dh, $some_dir) || die "Can't open $some_dir: $!";
+ while (readdir $dh) {
print "$some_dir/$_\n";
}
closedir $dh;
Reads from the filehandle whose typeglob is contained in EXPR (or from
C<*ARGV> if EXPR is not provided). In scalar context, each call reads and
returns the next line until end-of-file is reached, whereupon the
-subsequent call returns C<undef>. In list context, reads until end-of-file
-is reached and returns a list of lines. Note that the notion of "line"
-used here is whatever you may have defined with C<$/> or
-C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">.
+subsequent call returns L<C<undef>|/undef EXPR>. In list context, reads
+until end-of-file is reached and returns a list of lines. Note that the
+notion of "line" used here is whatever you may have defined with
+L<C<$E<sol>>|perlvar/$E<sol>> (or C<$INPUT_RECORD_SEPARATOR> in
+L<English>). See L<perlvar/"$/">.
-When C<$/> is set to C<undef>, when C<readline> is in scalar
-context (i.e., file slurp mode), and when an empty file is read, it
-returns C<''> the first time, followed by C<undef> subsequently.
+When L<C<$E<sol>>|perlvar/$E<sol>> is set to L<C<undef>|/undef EXPR>,
+when L<C<readline>|/readline EXPR> is in scalar context (i.e., file
+slurp mode), and when an empty file is read, it returns C<''> the first
+time, followed by L<C<undef>|/undef EXPR> subsequently.
This is the internal function implementing the C<< <EXPR> >>
operator, but you can use it directly. The C<< <EXPR> >>
operator is discussed in more detail in L<perlop/"I/O Operators">.
- $line = <STDIN>;
- $line = readline(*STDIN); # same thing
+ my $line = <STDIN>;
+ my $line = readline(STDIN); # same thing
-If C<readline> encounters an operating system error, C<$!> will be set
-with the corresponding error message. It can be helpful to check
-C<$!> when you are reading from filehandles you don't trust, such as a
-tty or a socket. The following example uses the operator form of
-C<readline> and dies if the result is not defined.
+If L<C<readline>|/readline EXPR> encounters an operating system error,
+L<C<$!>|perlvar/$!> will be set with the corresponding error message.
+It can be helpful to check L<C<$!>|perlvar/$!> when you are reading from
+filehandles you don't trust, such as a tty or a socket. The following
+example uses the operator form of L<C<readline>|/readline EXPR> and dies
+if the result is not defined.
while ( ! eof($fh) ) {
- defined( $_ = <$fh> ) or die "readline failed: $!";
+ defined( $_ = readline $fh ) or die "readline failed: $!";
...
}
-Note that you have can't handle C<readline> errors that way with the
-C<ARGV> filehandle. In that case, you have to open each element of
-C<@ARGV> yourself since C<eof> handles C<ARGV> differently.
+Note that you have can't handle L<C<readline>|/readline EXPR> errors
+that way with the C<ARGV> filehandle. In that case, you have to open
+each element of L<C<@ARGV>|perlvar/@ARGV> yourself since
+L<C<eof>|/eof FILEHANDLE> handles C<ARGV> differently.
foreach my $arg (@ARGV) {
open(my $fh, $arg) or warn "Can't open $arg: $!";
while ( ! eof($fh) ) {
- defined( $_ = <$fh> )
+ defined( $_ = readline $fh )
or die "readline failed for $arg: $!";
...
}
Returns the value of a symbolic link, if symbolic links are
implemented. If not, raises an exception. If there is a system
-error, returns the undefined value and sets C<$!> (errno). If EXPR is
-omitted, uses C<$_>.
+error, returns the undefined value and sets L<C<$!>|perlvar/$!> (errno).
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
Portability issues: L<perlport/readlink>.
The collected standard output of the command is returned.
In scalar context, it comes back as a single (potentially
multi-line) string. In list context, returns a list of lines
-(however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>).
+(however you've defined lines with L<C<$E<sol>>|perlvar/$E<sol>> (or
+C<$INPUT_RECORD_SEPARATOR> in L<English>)).
This is the internal function implementing the C<qx/EXPR/>
operator, but you can use it directly. The C<qx/EXPR/>
operator is discussed in more detail in L<perlop/"I/O Operators">.
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
=item recv SOCKET,SCALAR,LENGTH,FLAGS
X<recv>
same flags as the system call of the same name. Returns the address
of the sender if SOCKET's protocol supports this; returns an empty
string otherwise. If there's an error, returns the undefined value.
-This call is actually implemented in terms of recvfrom(2) system call.
+This call is actually implemented in terms of the L<recvfrom(2)> system call.
See L<perlipc/"UDP: Message Passing"> for examples.
Note the I<characters>: depending on the status of the socket, either
(8-bit) bytes or characters are received. By default all sockets
operate on bytes, but for example if the socket has been changed using
-binmode() to operate with the C<:encoding(utf8)> I/O layer (see the
-C<open> pragma, L<open>), the I/O will operate on UTF8-encoded Unicode
-characters, not bytes. Similarly for the C<:encoding> pragma: in that
+L<C<binmode>|/binmode FILEHANDLE, LAYER> to operate with the
+C<:encoding(utf8)> I/O layer (see the L<open> pragma), the I/O will
+operate on UTF8-encoded Unicode
+characters, not bytes. Similarly for the C<:encoding> layer: in that
case pretty much any characters can be read.
=item redo LABEL
=for Pod::Functions start this loop iteration over again
-The C<redo> command restarts the loop block without evaluating the
-conditional again. The C<continue> block, if any, is not executed. If
+The L<C<redo>|/redo LABEL> command restarts the loop block without
+evaluating the conditional again. The L<C<continue>|/continue BLOCK>
+block, if any, is not executed. If
the LABEL is omitted, the command refers to the innermost enclosing
loop. The C<redo EXPR> form, available starting in Perl 5.18.0, allows a
label name to be computed at run time, and is otherwise identical to C<redo
-LABEL>. Programs that want to lie to themselves about what was just input
+LABEL>. Programs that want to lie to themselves about what was just input
normally use this command:
# a simpleminded Pascal comment stripper
while (s|({.*}.*){.*}|$1 |) {}
s|{.*}| |;
if (s|{.*| |) {
- $front = $_;
+ my $front = $_;
while (<STDIN>) {
if (/}/) { # end of comment?
s|^|$front\{|;
print;
}
-C<redo> cannot be used to retry a block that returns a value such as
-C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit
-a grep() or map() operation.
+L<C<redo>|/redo LABEL> cannot be used to retry a block that returns a
+value such as C<eval {}>, C<sub {}>, or C<do {}>, and should not be used
+to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
+operation.
Note that a block by itself is semantically identical to a loop
-that executes once. Thus C<redo> inside such a block will effectively
-turn it into a looping construct.
+that executes once. Thus L<C<redo>|/redo LABEL> inside such a block
+will effectively turn it into a looping construct.
-See also L</continue> for an illustration of how C<last>, C<next>, and
-C<redo> work.
+See also L<C<continue>|/continue BLOCK> for an illustration of how
+L<C<last>|/last LABEL>, L<C<next>|/next LABEL>, and
+L<C<redo>|/redo LABEL> work.
Unlike most named operators, this has the same precedence as assignment.
It is also exempt from the looks-like-a-function rule, so
C<redo ("foo")."bar"> will cause "bar" to be part of the argument to
-C<redo>.
+L<C<redo>|/redo LABEL>.
=item ref EXPR
X<ref> X<reference>
=for Pod::Functions find out the type of thing being referenced
Returns a non-empty string if EXPR is a reference, the empty
-string otherwise. If EXPR is not specified, C<$_> will be used. The
-value returned depends on the type of thing the reference is a reference to.
+string otherwise. If EXPR is not specified, L<C<$_>|perlvar/$_> will be
+used. The value returned depends on the type of thing the reference is
+a reference to.
Builtin types include:
VSTRING
Regexp
-You can think of C<ref> as a C<typeof> operator.
+You can think of L<C<ref>|/ref EXPR> as a C<typeof> operator.
if (ref($r) eq "HASH") {
print "r is a reference to a hash.\n";
The return value C<LVALUE> indicates a reference to an lvalue that is not
a variable. You get this from taking the reference of function calls like
-C<pos()> or C<substr()>. C<VSTRING> is returned if the reference points
-to a L<version string|perldata/"Version Strings">.
+L<C<pos>|/pos SCALAR> or
+L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT>. C<VSTRING> is
+returned if the reference points to a
+L<version string|perldata/"Version Strings">.
The result C<Regexp> indicates that the argument is a regular expression
-resulting from C<qr//>.
+resulting from L<C<qrE<sol>E<sol>>|/qrE<sol>STRINGE<sol>>.
If the referenced object has been blessed into a package, then that package
name is returned instead. But don't use that, as it's now considered
"bad practice". For one reason, an object could be using a class called
-C<Regexp> or C<IO>, or even C<HASH>. Also, C<ref> doesn't take into account
-subclasses, like C<isa> does.
+C<Regexp> or C<IO>, or even C<HASH>. Also, L<C<ref>|/ref EXPR> doesn't
+take into account subclasses, like
+L<C<isa>|UNIVERSAL/C<< $obj->isa( TYPE ) >>> does.
-Instead, use C<blessed> (in the L<Scalar::Util> module) for boolean
-checks, C<isa> for specific class checks and C<reftype> (also from
-L<Scalar::Util>) for type checks. (See L<perlobj> for details and a
-C<blessed/isa> example.)
+Instead, use L<C<blessed>|Scalar::Util/blessed> (in the L<Scalar::Util>
+module) for boolean checks, L<C<isa>|UNIVERSAL/C<< $obj->isa( TYPE ) >>>
+for specific class checks and L<C<reftype>|Scalar::Util/reftype> (also
+from L<Scalar::Util>) for type checks. (See L<perlobj> for details and
+a L<C<blessed>|Scalar::Util/blessed>/L<C<isa>|UNIVERSAL/C<< $obj->isa( TYPE ) >>>
+example.)
See also L<perlref>.
boundaries, even though the system I<mv> command sometimes compensates
for this. Other restrictions include whether it works on directories,
open files, or pre-existing files. Check L<perlport> and either the
-rename(2) manpage or equivalent system documentation for details.
+L<rename(2)> manpage or equivalent system documentation for details.
-For a platform independent C<move> function look at the L<File::Copy>
-module.
+For a platform independent L<C<move>|File::Copy/move> function look at
+the L<File::Copy> module.
Portability issues: L<perlport/rename>.
=for Pod::Functions load in external functions from a library at runtime
Demands a version of Perl specified by VERSION, or demands some semantics
-specified by EXPR or by C<$_> if EXPR is not supplied.
+specified by EXPR or by L<C<$_>|perlvar/$_> if EXPR is not supplied.
VERSION may be either a numeric argument such as 5.006, which will be
-compared to C<$]>, or a literal of the form v5.6.1, which will be compared
-to C<$^V> (aka $PERL_VERSION). An exception is raised if
-VERSION is greater than the version of the current Perl interpreter.
-Compare with L</use>, which can do a similar check at compile time.
+compared to L<C<$]>|perlvar/$]>, or a literal of the form v5.6.1, which
+will be compared to L<C<$^V>|perlvar/$^V> (or C<$PERL_VERSION> in
+L<English>). An exception is raised if VERSION is greater than the
+version of the current Perl interpreter. Compare with
+L<C<use>|/use Module VERSION LIST>, which can do a similar check at
+compile time.
Specifying VERSION as a literal of the form v5.6.1 should generally be
avoided, because it leads to misleading error messages under earlier
require 5.006_001; # ditto; preferred for backwards
compatibility
-Otherwise, C<require> demands that a library file be included if it
-hasn't already been included. The file is included via the do-FILE
-mechanism, which is essentially just a variety of C<eval> with the
+Otherwise, L<C<require>|/require VERSION> demands that a library file be
+included if it hasn't already been included. The file is included via
+the do-FILE mechanism, which is essentially just a variety of
+L<C<eval>|/eval EXPR> with the
caveat that lexical variables in the invoking script will be invisible
to the included code. If it were implemented in pure Perl, it
would have semantics similar to the following:
otherwise. But it's better just to put the C<1;>, in case you add more
statements.
-If EXPR is a bareword, the require assumes a "F<.pm>" extension and
-replaces "F<::>" with "F</>" in the filename for you,
+If EXPR is a bareword, L<C<require>|/require VERSION> assumes a F<.pm>
+extension and replaces C<::> with C</> in the filename for you,
to make it easy to load standard modules. This form of loading of
modules does not risk altering your namespace.
require Foo::Bar; # a splendid bareword
-The require function will actually look for the "F<Foo/Bar.pm>" file in the
-directories specified in the C<@INC> array.
+The require function will actually look for the F<Foo/Bar.pm> file in the
+directories specified in the L<C<@INC>|perlvar/@INC> array.
But if you try this:
- $class = 'Foo::Bar';
+ my $class = 'Foo::Bar';
require $class; # $class is not a bareword
#or
require "Foo::Bar"; # not a bareword because of the ""
-The require function will look for the "F<Foo::Bar>" file in the @INC array and
-will complain about not finding "F<Foo::Bar>" there. In this case you can do:
+The require function will look for the F<Foo::Bar> file in the
+L<C<@INC>|perlvar/@INC> array and
+will complain about not finding F<Foo::Bar> there. In this case you can do:
eval "require $class";
-Now that you understand how C<require> looks for files with a
-bareword argument, there is a little extra functionality going on behind
-the scenes. Before C<require> looks for a "F<.pm>" extension, it will
-first look for a similar filename with a "F<.pmc>" extension. If this file
-is found, it will be loaded in place of any file ending in a "F<.pm>"
-extension.
+Now that you understand how L<C<require>|/require VERSION> looks for
+files with a bareword argument, there is a little extra functionality
+going on behind the scenes. Before L<C<require>|/require VERSION> looks
+for a F<.pm> extension, it will first look for a similar filename with a
+F<.pmc> extension. If this file is found, it will be loaded in place of
+any file ending in a F<.pm> extension.
You can also insert hooks into the import facility by putting Perl code
-directly into the @INC array. There are three forms of hooks: subroutine
-references, array references, and blessed objects.
+directly into the L<C<@INC>|perlvar/@INC> array. There are three forms
+of hooks: subroutine references, array references, and blessed objects.
Subroutine references are the simplest case. When the inclusion system
-walks through @INC and encounters a subroutine, this subroutine gets
-called with two parameters, the first a reference to itself, and the
-second the name of the file to be included (e.g., "F<Foo/Bar.pm>"). The
-subroutine should return either nothing or else a list of up to four
-values in the following order:
+walks through L<C<@INC>|perlvar/@INC> and encounters a subroutine, this
+subroutine gets called with two parameters, the first a reference to
+itself, and the second the name of the file to be included (e.g.,
+F<Foo/Bar.pm>). The subroutine should return either nothing or else a
+list of up to four values in the following order:
=over
=item 2
-A filehandle, from which the file will be read.
+A filehandle, from which the file will be read.
=item 3
A reference to a subroutine. If there is no filehandle (previous item),
then this subroutine is expected to generate one line of source code per
-call, writing the line into C<$_> and returning 1, then finally at end of
-file returning 0. If there is a filehandle, then the subroutine will be
-called to act as a simple source filter, with the line as read in C<$_>.
+call, writing the line into L<C<$_>|perlvar/$_> and returning 1, then
+finally at end of file returning 0. If there is a filehandle, then the
+subroutine will be called to act as a simple source filter, with the
+line as read in L<C<$_>|perlvar/$_>.
Again, return 1 for each valid line, and 0 after all lines have been
returned.
=back
-If an empty list, C<undef>, or nothing that matches the first 3 values above
-is returned, then C<require> looks at the remaining elements of @INC.
+If an empty list, L<C<undef>|/undef EXPR>, or nothing that matches the
+first 3 values above is returned, then L<C<require>|/require VERSION>
+looks at the remaining elements of L<C<@INC>|perlvar/@INC>.
Note that this filehandle must be a real filehandle (strictly a typeglob
-or reference to a typeglob, whether blessed or unblessed); tied filehandles
+or reference to a typeglob, whether blessed or unblessed); tied filehandles
will be ignored and processing will stop there.
If the hook is an array reference, its first element must be a subroutine
sub my_sub {
my ($arrayref, $filename) = @_;
# Retrieve $x, $y, ...
- my @parameters = @$arrayref[1..$#$arrayref];
+ my (undef, @parameters) = @$arrayref;
...
}
-If the hook is an object, it must provide an INC method that will be
+If the hook is an object, it must provide an C<INC> method that will be
called as above, the first parameter being the object itself. (Note that
you must fully qualify the sub's name, as unqualified C<INC> is always forced
into package C<main>.) Here is a typical code layout:
# In the main program
push @INC, Foo->new(...);
-These hooks are also permitted to set the %INC entry
+These hooks are also permitted to set the L<C<%INC>|perlvar/%INC> entry
corresponding to the files they have loaded. See L<perlvar/%INC>.
-For a yet-more-powerful import facility, see L</use> and L<perlmod>.
+For a yet-more-powerful import facility, see
+L<C<use>|/use Module VERSION LIST> and L<perlmod>.
=item reset EXPR
X<reset>
=for Pod::Functions clear all variables of a given name
-Generally used in a C<continue> block at the end of a loop to clear
-variables and reset C<??> searches so that they work again. The
+Generally used in a L<C<continue>|/continue BLOCK> block at the end of a
+loop to clear variables and reset C<m?pattern?> searches so that they
+work again. The
expression is interpreted as a list of single characters (hyphens
allowed for ranges). All variables and arrays beginning with one of
those letters are reset to their pristine state. If the expression is
-omitted, one-match searches (C<?pattern?>) are reset to match again.
+omitted, one-match searches (C<m?pattern?>) are reset to match again.
Only resets variables or searches in the current package. Always returns
1. Examples:
reset 'X'; # reset all X variables
reset 'a-z'; # reset lower case variables
- reset; # just reset ?one-time? searches
+ reset; # just reset m?one-time? searches
Resetting C<"A-Z"> is not recommended because you'll wipe out your
-C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package
-variables; lexical variables are unaffected, but they clean themselves
-up on scope exit anyway, so you'll probably want to use them instead.
-See L</my>.
+L<C<@ARGV>|perlvar/@ARGV> and L<C<@INC>|perlvar/@INC> arrays and your
+L<C<%ENV>|perlvar/%ENV> hash.
+Resets only package variables; lexical variables are unaffected, but
+they clean themselves up on scope exit anyway, so you'll probably want
+to use them instead. See L<C<my>|/my VARLIST>.
=item return EXPR
X<return>
=for Pod::Functions get out of a function early
-Returns from a subroutine, C<eval>, or C<do FILE> with the value
+Returns from a subroutine, L<C<eval>|/eval EXPR>,
+L<C<do FILE>|/do EXPR>, L<C<sort>|/sort SUBNAME LIST> block or regex
+eval block (but not a L<C<grep>|/grep BLOCK LIST> or
+L<C<map>|/map BLOCK LIST> block) with the value
given in EXPR. Evaluation of EXPR may be in list, scalar, or void
context, depending on how the return value will be used, and the context
-may vary from one execution to the next (see L</wantarray>). If no EXPR
+may vary from one execution to the next (see
+L<C<wantarray>|/wantarray>). If no EXPR
is given, returns an empty list in list context, the undefined value in
scalar context, and (of course) nothing at all in void context.
-(In the absence of an explicit C<return>, a subroutine, eval,
-or do FILE automatically returns the value of the last expression
+(In the absence of an explicit L<C<return>|/return EXPR>, a subroutine,
+L<C<eval>|/eval EXPR>,
+or L<C<do FILE>|/do EXPR> automatically returns the value of the last expression
evaluated.)
Unlike most named operators, this is also exempt from the
looks-like-a-function rule, so C<return ("foo")."bar"> will
-cause "bar" to be part of the argument to C<return>.
+cause C<"bar"> to be part of the argument to L<C<return>|/return EXPR>.
=item reverse LIST
X<reverse> X<rev> X<invert>
print scalar reverse "dlrow ,", "olleH"; # Hello, world
-Used without arguments in scalar context, reverse() reverses C<$_>.
+Used without arguments in scalar context, L<C<reverse>|/reverse LIST>
+reverses L<C<$_>|perlvar/$_>.
$_ = "dlrow ,olleH";
print reverse; # No output, list context
unwind one hash and build a whole new one, which may take some time
on a large hash, such as from a DBM file.
- %by_name = reverse %by_address; # Invert the hash
+ my %by_name = reverse %by_address; # Invert the hash
=item rewinddir DIRHANDLE
X<rewinddir>
=for Pod::Functions reset directory handle
Sets the current position to the beginning of the directory for the
-C<readdir> routine on DIRHANDLE.
+L<C<readdir>|/readdir DIRHANDLE> routine on DIRHANDLE.
Portability issues: L<perlport/rewinddir>.
=for Pod::Functions right-to-left substring search
-Works just like index() except that it returns the position of the I<last>
+Works just like L<C<index>|/index STR,SUBSTR,POSITION> except that it
+returns the position of the I<last>
occurrence of SUBSTR in STR. If POSITION is specified, returns the
last occurrence beginning at or before that position.
Deletes the directory specified by FILENAME if that directory is
empty. If it succeeds it returns true; otherwise it returns false and
-sets C<$!> (errno). If FILENAME is omitted, uses C<$_>.
+sets L<C<$!>|perlvar/$!> (errno). If FILENAME is omitted, uses
+L<C<$_>|perlvar/$_>.
To remove a directory tree recursively (C<rm -rf> on Unix) look at
-the C<rmtree> function of the L<File::Path> module.
+the L<C<rmtree>|File::Path/rmtree( $dir )> function of the L<File::Path>
+module.
=item s///
=for Pod::Functions +say output a list to a filehandle, appending a newline
-Just like C<print>, but implicitly appends a newline. C<say LIST> is
-simply an abbreviation for C<{ local $\ = "\n"; print LIST }>. To use
-FILEHANDLE without a LIST to print the contents of C<$_> to it, you must
-use a real filehandle like C<FH>, not an indirect one like C<$fh>.
+Just like L<C<print>|/print FILEHANDLE LIST>, but implicitly appends a
+newline. C<say LIST> is simply an abbreviation for
+C<{ local $\ = "\n"; print LIST }>. To use FILEHANDLE without a LIST to
+print the contents of L<C<$_>|perlvar/$_> to it, you must use a bareword
+filehandle like C<FH>, not an indirect one like C<$fh>.
-This keyword is available only when the C<"say"> feature
-is enabled, or when prefixed with C<CORE::>; see
-L<feature>. Alternately, include a C<use v5.10> or later to the current
-scope.
+L<C<say>|/say FILEHANDLE LIST> is available only if the
+L<C<"say"> feature|feature/The 'say' feature> is enabled or if it is
+prefixed with C<CORE::>. The
+L<C<"say"> feature|feature/The 'say' feature> is enabled automatically
+with a C<use v5.10> (or higher) declaration in the current scope.
=item scalar EXPR
X<scalar> X<context>
Forces EXPR to be interpreted in scalar context and returns the value
of EXPR.
- @counts = ( scalar @a, scalar @b, scalar @c );
+ my @counts = ( scalar @a, scalar @b, scalar @c );
There is no equivalent operator to force an expression to
be interpolated in list context because in practice, this is never
the construction C<@{[ (some expression) ]}>, but usually a simple
C<(some expression)> suffices.
-Because C<scalar> is a unary operator, if you accidentally use a
+Because L<C<scalar>|/scalar EXPR> is a unary operator, if you
+accidentally use a
parenthesized list for the EXPR, this behaves as a scalar comma expression,
evaluating all but the last element in void context and returning the final
element evaluated in scalar context. This is seldom what you want.
The following single statement:
- print uc(scalar(&foo,$bar)),$baz;
+ print uc(scalar(foo(), $bar)), $baz;
is the moral equivalent of these two:
- &foo;
- print(uc($bar),$baz);
+ foo();
+ print(uc($bar), $baz);
-See L<perlop> for more details on unary operators and the comma operator.
+See L<perlop> for more details on unary operators and the comma operator,
+and L<perldata> for details on evaluating a hash in scalar contex.
=item seek FILEHANDLE,POSITION,WHENCE
X<seek> X<fseek> X<filehandle, position>
=for Pod::Functions reposition file pointer for random-access I/O
-Sets FILEHANDLE's position, just like the C<fseek> call of C<stdio>.
+Sets FILEHANDLE's position, just like the L<fseek(3)> call of C C<stdio>.
FILEHANDLE may be an expression whose value gives the name of the
filehandle. The values for WHENCE are C<0> to set the new position
I<in bytes> to POSITION; C<1> to set it to the current position plus
of the file) from the L<Fcntl> module. Returns C<1> on success, false
otherwise.
-Note the I<in bytes>: even if the filehandle has been set to
-operate on characters (for example by using the C<:encoding(utf8)> open
-layer), tell() will return byte offsets, not character offsets
-(because implementing that would render seek() and tell() rather slow).
-
-If you want to position the file for C<sysread> or C<syswrite>, don't use
-C<seek>, because buffering makes its effect on the file's read-write position
-unpredictable and non-portable. Use C<sysseek> instead.
+Note the emphasis on bytes: even if the filehandle has been set to operate
+on characters (for example using the C<:encoding(utf8)> I/O layer), the
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<tell>|/tell FILEHANDLE>, and
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE>
+family of functions use byte offsets, not character offsets,
+because seeking to a character offset would be very slow in a UTF-8 file.
+
+If you want to position the file for
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET> or
+L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET>, don't use
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>, because buffering makes its
+effect on the file's read-write position unpredictable and non-portable.
+Use L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE> instead.
Due to the rules and rigors of ANSI C, on some systems you have to do a
seek whenever you switch between reading and writing. Amongst other
-things, this may have the effect of calling stdio's clearerr(3).
+things, this may have the effect of calling stdio's L<clearerr(3)>.
A WHENCE of C<1> (C<SEEK_CUR>) is useful for not moving the file position:
- seek(TEST,0,1);
+ seek($fh, 0, 1);
This is also useful for applications emulating C<tail -f>. Once you hit
EOF on your read and then sleep for a while, you (probably) have to stick in a
-dummy seek() to reset things. The C<seek> doesn't change the position,
+dummy L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE> to reset things. The
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE> doesn't change the position,
but it I<does> clear the end-of-file condition on the handle, so that the
-next C<< <FILE> >> makes Perl try again to read something. (We hope.)
+next C<readline FILE> makes Perl try again to read something. (We hope.)
If that doesn't work (some I/O implementations are particularly
cantankerous), you might need something like this:
for (;;) {
- for ($curpos = tell(FILE); $_ = <FILE>;
- $curpos = tell(FILE)) {
+ for ($curpos = tell($fh); $_ = readline($fh);
+ $curpos = tell($fh)) {
# search for some stuff and put it into files
}
sleep($for_a_while);
- seek(FILE, $curpos, 0);
+ seek($fh, $curpos, 0);
}
=item seekdir DIRHANDLE,POS
=for Pod::Functions reposition directory pointer
-Sets the current position for the C<readdir> routine on DIRHANDLE. POS
-must be a value returned by C<telldir>. C<seekdir> also has the same caveats
-about possible directory compaction as the corresponding system library
-routine.
+Sets the current position for the L<C<readdir>|/readdir DIRHANDLE>
+routine on DIRHANDLE. POS must be a value returned by
+L<C<telldir>|/telldir DIRHANDLE>. L<C<seekdir>|/seekdir DIRHANDLE,POS>
+also has the same caveats about possible directory compaction as the
+corresponding system library routine.
=item select FILEHANDLE
X<select> X<filehandle, default>
Returns the currently selected filehandle. If FILEHANDLE is supplied,
sets the new current default filehandle for output. This has two
-effects: first, a C<write> or a C<print> without a filehandle
+effects: first, a L<C<write>|/write FILEHANDLE> or a L<C<print>|/print
+FILEHANDLE LIST> without a filehandle
default to this FILEHANDLE. Second, references to variables related to
-output will refer to this output channel.
+output will refer to this output channel.
For example, to set the top-of-form format for more than one
output channel, you might do the following:
FILEHANDLE may be an expression whose value gives the name of the
actual filehandle. Thus:
- $oldfh = select(STDERR); $| = 1; select($oldfh);
+ my $oldfh = select(STDERR); $| = 1; select($oldfh);
Some programmers may prefer to think of filehandles as objects with
methods, preferring to write the last example as:
- use IO::Handle;
STDERR->autoflush(1);
+(Prior to Perl version 5.14, you have to C<use IO::Handle;> explicitly
+first.)
+
Portability issues: L<perlport/select>.
=item select RBITS,WBITS,EBITS,TIMEOUT
X<select>
-This calls the select(2) syscall with the bit masks specified, which
-can be constructed using C<fileno> and C<vec>, along these lines:
+This calls the L<select(2)> syscall with the bit masks specified, which
+can be constructed using L<C<fileno>|/fileno FILEHANDLE> and
+L<C<vec>|/vec EXPR,OFFSET,BITS>, along these lines:
- $rin = $win = $ein = '';
+ my $rin = my $win = my $ein = '';
vec($rin, fileno(STDIN), 1) = 1;
vec($win, fileno(STDOUT), 1) = 1;
$ein = $rin | $win;
}
return $bits;
}
- $rin = fhbits(*STDIN, *TTY, *MYSOCK);
+ my $rin = fhbits(\*STDIN, $tty, $mysock);
The usual idiom is:
- ($nfound,$timeleft) =
- select($rout=$rin, $wout=$win, $eout=$ein, $timeout);
+ my ($nfound, $timeleft) =
+ select(my $rout = $rin, my $wout = $win, my $eout = $ein,
+ $timeout);
or to block until something becomes ready just do this
- $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);
+ my $nfound =
+ select(my $rout = $rin, my $wout = $win, my $eout = $ein, undef);
-Most systems do not bother to return anything useful in $timeleft, so
-calling select() in scalar context just returns $nfound.
+Most systems do not bother to return anything useful in C<$timeleft>, so
+calling L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT> in scalar context
+just returns C<$nfound>.
-Any of the bit masks can also be undef. The timeout, if specified, is
+Any of the bit masks can also be L<C<undef>|/undef EXPR>. The timeout,
+if specified, is
in seconds, which may be fractional. Note: not all implementations are
-capable of returning the $timeleft. If not, they always return
-$timeleft equal to the supplied $timeout.
+capable of returning the C<$timeleft>. If not, they always return
+C<$timeleft> equal to the supplied C<$timeout>.
You can effect a sleep of 250 milliseconds this way:
select(undef, undef, undef, 0.25);
-Note that whether C<select> gets restarted after signals (say, SIGALRM)
-is implementation-dependent. See also L<perlport> for notes on the
-portability of C<select>.
+Note that whether L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT> gets
+restarted after signals (say, SIGALRM) is implementation-dependent. See
+also L<perlport> for notes on the portability of
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT>.
-On error, C<select> behaves just like select(2): it returns
--1 and sets C<$!>.
+On error, L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT> behaves just
+like L<select(2)>: it returns C<-1> and sets L<C<$!>|perlvar/$!>.
-On some Unixes, select(2) may report a socket file descriptor as "ready for
-reading" even when no data is available, and thus any subsequent C<read>
-would block. This can be avoided if you always use O_NONBLOCK on the
-socket. See select(2) and fcntl(2) for further details.
+On some Unixes, L<select(2)> may report a socket file descriptor as
+"ready for reading" even when no data is available, and thus any
+subsequent L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET> would block.
+This can be avoided if you always use C<O_NONBLOCK> on the socket. See
+L<select(2)> and L<fcntl(2)> for further details.
-The standard C<IO::Select> module provides a user-friendlier interface
-to C<select>, mostly because it does all the bit-mask work for you.
+The standard L<C<IO::Select>|IO::Select> module provides a
+user-friendlier interface to
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT>, mostly because it does
+all the bit-mask work for you.
-B<WARNING>: One should not attempt to mix buffered I/O (like C<read>
-or <FH>) with C<select>, except as permitted by POSIX, and even
-then only on POSIX systems. You have to use C<sysread> instead.
+B<WARNING>: One should not attempt to mix buffered I/O (like
+L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET> or
+L<C<readline>|/readline EXPR>) with
+L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT>, except as permitted by
+POSIX, and even then only on POSIX systems. You have to use
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET> instead.
Portability issues: L<perlport/select>.
=for Pod::Functions SysV semaphore control operations
-Calls the System V IPC function semctl(2). You'll probably have to say
+Calls the System V IPC function L<semctl(2)>. You'll probably have to say
use IPC::SysV;
first to get the correct constant definitions. If CMD is IPC_STAT or
GETALL, then ARG must be a variable that will hold the returned
-semid_ds structure or semaphore value array. Returns like C<ioctl>:
+semid_ds structure or semaphore value array. Returns like
+L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>:
the undefined value for error, "C<0 but true>" for zero, or the actual
return value otherwise. The ARG must consist of a vector of native
short integers, which may be created with C<pack("s!",(0)x$nsem)>.
-See also L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::Semaphore>
-documentation.
+See also L<perlipc/"SysV IPC"> and the documentation for
+L<C<IPC::SysV>|IPC::SysV> and L<C<IPC::Semaphore>|IPC::Semaphore>.
Portability issues: L<perlport/semctl>.
=for Pod::Functions get set of SysV semaphores
-Calls the System V IPC function semget(2). Returns the semaphore id, or
+Calls the System V IPC function L<semget(2)>. Returns the semaphore id, or
the undefined value on error. See also
-L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::SysV::Semaphore>
-documentation.
+L<perlipc/"SysV IPC"> and the documentation for
+L<C<IPC::SysV>|IPC::SysV> and L<C<IPC::Semaphore>|IPC::Semaphore>.
Portability issues: L<perlport/semget>.
=for Pod::Functions SysV semaphore operations
-Calls the System V IPC function semop(2) for semaphore operations
+Calls the System V IPC function L<semop(2)> for semaphore operations
such as signalling and waiting. OPSTRING must be a packed array of
semop structures. Each semop structure can be generated with
-C<pack("s!3", $semnum, $semop, $semflag)>. The length of OPSTRING
+C<pack("s!3", $semnum, $semop, $semflag)>. The length of OPSTRING
implies the number of semaphore operations. Returns true if
successful, false on error. As an example, the
following code waits on semaphore $semnum of semaphore id $semid:
- $semop = pack("s!3", $semnum, -1, 0);
+ my $semop = pack("s!3", $semnum, -1, 0);
die "Semaphore trouble: $!\n" unless semop($semid, $semop);
To signal the semaphore, replace C<-1> with C<1>. See also
-L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::SysV::Semaphore>
-documentation.
+L<perlipc/"SysV IPC"> and the documentation for
+L<C<IPC::SysV>|IPC::SysV> and L<C<IPC::Semaphore>|IPC::Semaphore>.
Portability issues: L<perlport/semop>.
Sends a message on a socket. Attempts to send the scalar MSG to the SOCKET
filehandle. Takes the same flags as the system call of the same name. On
unconnected sockets, you must specify a destination to I<send to>, in which
-case it does a sendto(2) syscall. Returns the number of characters sent,
-or the undefined value on error. The sendmsg(2) syscall is currently
+case it does a L<sendto(2)> syscall. Returns the number of characters sent,
+or the undefined value on error. The L<sendmsg(2)> syscall is currently
unimplemented. See L<perlipc/"UDP: Message Passing"> for examples.
Note the I<characters>: depending on the status of the socket, either
(8-bit) bytes or characters are sent. By default all sockets operate
on bytes, but for example if the socket has been changed using
-binmode() to operate with the C<:encoding(utf8)> I/O layer (see
-L</open>, or the C<open> pragma, L<open>), the I/O will operate on UTF-8
+L<C<binmode>|/binmode FILEHANDLE, LAYER> to operate with the
+C<:encoding(utf8)> I/O layer (see L<C<open>|/open FILEHANDLE,EXPR>, or
+the L<open> pragma), the I/O will operate on UTF-8
encoded Unicode characters, not bytes. Similarly for the C<:encoding>
-pragma: in that case pretty much any characters can be sent.
+layer: in that case pretty much any characters can be sent.
=item setpgrp PID,PGRP
X<setpgrp> X<group>
Sets the current process group for the specified PID, C<0> for the current
process. Raises an exception when used on a machine that doesn't
-implement POSIX setpgid(2) or BSD setpgrp(2). If the arguments are omitted,
-it defaults to C<0,0>. Note that the BSD 4.2 version of C<setpgrp> does not
-accept any arguments, so only C<setpgrp(0,0)> is portable. See also
-C<POSIX::setsid()>.
+implement POSIX L<setpgid(2)> or BSD L<setpgrp(2)>. If the arguments
+are omitted, it defaults to C<0,0>. Note that the BSD 4.2 version of
+L<C<setpgrp>|/setpgrp PID,PGRP> does not accept any arguments, so only
+C<setpgrp(0,0)> is portable. See also
+L<C<POSIX::setsid()>|POSIX/C<setsid>>.
Portability issues: L<perlport/setpgrp>.
=for Pod::Functions set a process's nice value
Sets the current priority for a process, a process group, or a user.
-(See setpriority(2).) Raises an exception when used on a machine
-that doesn't implement setpriority(2).
+(See L<setpriority(2)>.) Raises an exception when used on a machine
+that doesn't implement L<setpriority(2)>.
Portability issues: L<perlport/setpriority>.
=for Pod::Functions set some socket options
-Sets the socket option requested. Returns C<undef> on error.
-Use integer constants provided by the C<Socket> module for
+Sets the socket option requested. Returns L<C<undef>|/undef EXPR> on
+error. Use integer constants provided by the L<C<Socket>|Socket> module
+for
LEVEL and OPNAME. Values for LEVEL can also be obtained from
getprotobyname. OPTVAL might either be a packed string or an integer.
An integer OPTVAL is shorthand for pack("i", OPTVAL).
=item shift ARRAY
X<shift>
-=item shift EXPR
-
=item shift
=for Pod::Functions remove the first element of an array, and return it
Shifts the first value of the array off and returns it, shortening the
array by 1 and moving everything down. If there are no elements in the
array, returns the undefined value. If ARRAY is omitted, shifts the
-C<@_> array within the lexical scope of subroutines and formats, and the
-C<@ARGV> array outside a subroutine and also within the lexical scopes
+L<C<@_>|perlvar/@_> array within the lexical scope of subroutines and
+formats, and the L<C<@ARGV>|perlvar/@ARGV> array outside a subroutine
+and also within the lexical scopes
established by the C<eval STRING>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>,
C<UNITCHECK {}>, and C<END {}> constructs.
-Starting with Perl 5.14, C<shift> can take a scalar EXPR, which must hold a
-reference to an unblessed array. The argument will be dereferenced
-automatically. This aspect of C<shift> is considered highly experimental.
-The exact behaviour may change in a future version of Perl.
+Starting with Perl 5.14, an experimental feature allowed
+L<C<shift>|/shift ARRAY> to take a
+scalar expression. This experiment has been deemed unsuccessful, and was
+removed as of Perl 5.24.
-To avoid confusing would-be users of your code who are running earlier
-versions of Perl with mysterious syntax errors, put this sort of thing at
-the top of your file to signal that your code will work I<only> on Perls of
-a recent vintage:
-
- use 5.014; # so push/pop/etc work on scalars (experimental)
-
-See also C<unshift>, C<push>, and C<pop>. C<shift> and C<unshift> do the
-same thing to the left end of an array that C<pop> and C<push> do to the
-right end.
+See also L<C<unshift>|/unshift ARRAY,LIST>, L<C<push>|/push ARRAY,LIST>,
+and L<C<pop>|/pop ARRAY>. L<C<shift>|/shift ARRAY> and
+L<C<unshift>|/unshift ARRAY,LIST> do the same thing to the left end of
+an array that L<C<pop>|/pop ARRAY> and L<C<push>|/push ARRAY,LIST> do to
+the right end.
=item shmctl ID,CMD,ARG
X<shmctl>
first to get the correct constant definitions. If CMD is C<IPC_STAT>,
then ARG must be a variable that will hold the returned C<shmid_ds>
-structure. Returns like ioctl: C<undef> for error; "C<0> but
-true" for zero; and the actual return value otherwise.
-See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
+structure. Returns like ioctl: L<C<undef>|/undef EXPR> for error; "C<0>
+but true" for zero; and the actual return value otherwise.
+See also L<perlipc/"SysV IPC"> and the documentation for
+L<C<IPC::SysV>|IPC::SysV>.
Portability issues: L<perlport/shmctl>.
=for Pod::Functions get SysV shared memory segment identifier
Calls the System V IPC function shmget. Returns the shared memory
-segment id, or C<undef> on error.
-See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
+segment id, or L<C<undef>|/undef EXPR> on error.
+See also L<perlipc/"SysV IPC"> and the documentation for
+L<C<IPC::SysV>|IPC::SysV>.
Portability issues: L<perlport/shmget>.
hold the data read. When writing, if STRING is too long, only SIZE
bytes are used; if STRING is too short, nulls are written to fill out
SIZE bytes. Return true if successful, false on error.
-shmread() taints the variable. See also L<perlipc/"SysV IPC">,
-C<IPC::SysV>, and the C<IPC::Shareable> module from CPAN.
+L<C<shmread>|/shmread ID,VAR,POS,SIZE> taints the variable. See also
+L<perlipc/"SysV IPC"> and the documentation for
+L<C<IPC::SysV>|IPC::SysV> and the L<C<IPC::Shareable>|IPC::Shareable>
+module from CPAN.
Portability issues: L<perlport/shmread> and L<perlport/shmwrite>.
Shuts down a socket connection in the manner indicated by HOW, which
has the same interpretation as in the syscall of the same name.
- shutdown(SOCKET, 0); # I/we have stopped reading data
- shutdown(SOCKET, 1); # I/we have stopped writing data
- shutdown(SOCKET, 2); # I/we have stopped using this socket
+ shutdown($socket, 0); # I/we have stopped reading data
+ shutdown($socket, 1); # I/we have stopped writing data
+ shutdown($socket, 2); # I/we have stopped using this socket
This is useful with sockets when you want to tell the other
side you're done writing but not done reading, or vice versa.
disables the file descriptor in any forked copies in other
processes.
-Returns C<1> for success; on error, returns C<undef> if
+Returns C<1> for success; on error, returns L<C<undef>|/undef EXPR> if
the first argument is not a valid filehandle, or returns C<0> and sets
-C<$!> for any other failure.
+L<C<$!>|perlvar/$!> for any other failure.
=item sin EXPR
X<sin> X<sine> X<asin> X<arcsine>
=for Pod::Functions return the sine of a number
Returns the sine of EXPR (expressed in radians). If EXPR is omitted,
-returns sine of C<$_>.
+returns sine of L<C<$_>|perlvar/$_>.
For the inverse sine operation, you may use the C<Math::Trig::asin>
function, or use this relation:
=for Pod::Functions block for some number of seconds
-Causes the script to sleep for (integer) EXPR seconds, or forever if no
-argument is given. Returns the integer number of seconds actually slept.
+Causes the script to sleep for (integer) EXPR seconds, or forever if no
+argument is given. Returns the integer number of seconds actually slept.
May be interrupted if the process receives a signal such as C<SIGALRM>.
eval {
- local $SIG{ALARM} = sub { die "Alarm!\n" };
+ local $SIG{ALRM} = sub { die "Alarm!\n" };
sleep;
};
die $@ unless $@ eq "Alarm!\n";
-You probably cannot mix C<alarm> and C<sleep> calls, because C<sleep>
-is often implemented using C<alarm>.
+You probably cannot mix L<C<alarm>|/alarm SECONDS> and
+L<C<sleep>|/sleep EXPR> calls, because L<C<sleep>|/sleep EXPR> is often
+implemented using L<C<alarm>|/alarm SECONDS>.
On some older systems, it may sleep up to a full second less than what
you requested, depending on how it counts seconds. Most modern systems
however, because your process might not be scheduled right away in a
busy multitasking system.
-For delays of finer granularity than one second, the Time::HiRes module
-(from CPAN, and starting from Perl 5.8 part of the standard
-distribution) provides usleep(). You may also use Perl's four-argument
-version of select() leaving the first three arguments undefined, or you
-might be able to use the C<syscall> interface to access setitimer(2) if
-your system supports it. See L<perlfaq8> for details.
+For delays of finer granularity than one second, the L<Time::HiRes>
+module (from CPAN, and starting from Perl 5.8 part of the standard
+distribution) provides L<C<usleep>|Time::HiRes/usleep ( $useconds )>.
+You may also use Perl's four-argument
+version of L<C<select>|/select RBITS,WBITS,EBITS,TIMEOUT> leaving the
+first three arguments undefined, or you might be able to use the
+L<C<syscall>|/syscall NUMBER, LIST> interface to access L<setitimer(2)>
+if your system supports it. See L<perlfaq8> for details.
-See also the POSIX module's C<pause> function.
+See also the L<POSIX> module's L<C<pause>|POSIX/C<pause>> function.
=item socket SOCKET,DOMAIN,TYPE,PROTOCOL
X<socket>
On systems that support a close-on-exec flag on files, the flag will
be set for the newly opened file descriptor, as determined by the
-value of
$^F. See L<perlvar/$^F>.
+value of
L<C<$^F>|perlvar/$^F>. See L<perlvar/$^F>.
=item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
X<socketpair>
On systems that support a close-on-exec flag on files, the flag will
be set for the newly opened file descriptors, as determined by the value
-of
$^F. See L<perlvar/$^F>.
+of
L<C<$^F>|perlvar/$^F>. See L<perlvar/$^F>.
-Some systems defined C<pipe> in terms of C<socketpair>, in which a call
-to C<pipe(Rdr, Wtr)> is essentially:
+Some systems define L<C<pipe>|/pipe READHANDLE,WRITEHANDLE> in terms of
+L<C<socketpair>|/socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL>, in
+which a call to C<pipe($rdr, $wtr)> is essentially:
use Socket;
- socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
- shutdown(Rdr, 1); # no more writing for reader
- shutdown(Wtr, 0); # no more reading for writer
+ socketpair(my $rdr, my $wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
+ shutdown($rdr, 1); # no more writing for reader
+ shutdown($wtr, 0); # no more reading for writer
See L<perlipc> for an example of socketpair use. Perl 5.8 and later will
emulate socketpair using IP sockets to localhost if your system implements
=for Pod::Functions sort a list of values
In list context, this sorts the LIST and returns the sorted list value.
-In scalar context, the behaviour of C<sort()> is undefined.
+In scalar context, the behaviour of L<C<sort>|/sort SUBNAME LIST> is
+undefined.
-If SUBNAME or BLOCK is omitted, C<sort>s in standard string comparison
+If SUBNAME or BLOCK is omitted, L<C<sort>|/sort SUBNAME LIST>s in
+standard string comparison
order. If SUBNAME is specified, it gives the name of a subroutine
that returns an integer less than, equal to, or greater than C<0>,
-depending on how the elements of the list are to be ordered. (The
+depending on how the elements of the list are to be ordered. (The
C<< <=> >> and C<cmp> operators are extremely useful in such routines.)
SUBNAME may be a scalar variable name (unsubscripted), in which case
the value provides the name of (or a reference to) the actual
an anonymous, in-line sort subroutine.
If the subroutine's prototype is C<($$)>, the elements to be compared are
-passed by reference in C<@_>, as for a normal subroutine. This is slower
-than unprototyped subroutines, where the elements to be compared are passed
-into the subroutine as the package global variables $a and $b (see example
-below). Note that in the latter case, it is usually highly counter-productive
-to declare $a and $b as lexicals.
+passed by reference in L<C<@_>|perlvar/@_>, as for a normal subroutine.
+This is slower than unprototyped subroutines, where the elements to be
+compared are passed into the subroutine as the package global variables
+C<$a> and C<$b> (see example below). Note that in the latter case, it
+is usually highly counter-productive to declare C<$a> and C<$b> as
+lexicals.
-If the subroutine is an XSUB, the elements to be compared are pushed on to
-the stack, the way arguments are usually passed to XSUBs. $a and $b are
-not set.
+If the subroutine is an XSUB, the elements to be compared are pushed on
+to the stack, the way arguments are usually passed to XSUBs. C<$a> and
+C<$b> are not set.
The values to be compared are always passed by reference and should not
be modified.
You also cannot exit out of the sort block or subroutine using any of the
-loop control operators described in L<perlsyn> or with C<goto>.
+loop control operators described in L<perlsyn> or with
+L<C<goto>|/goto LABEL>.
-When C<use locale> (but not C<use locale 'not_characters'>) is in
-effect, C<sort LIST> sorts LIST according to the
+When L<C<use locale>|locale> (but not C<use locale ':not_characters'>)
+is in effect, C<sort LIST> sorts LIST according to the
current collation locale. See L<perllocale>.
-sort() returns aliases into the original list, much as a for loop's index
-variable aliases the list elements. That is, modifying an element of a
-list returned by sort() (for example, in a C<foreach>, C<map> or C<grep>)
+L<C<sort>|/sort SUBNAME LIST> returns aliases into the original list,
+much as a for loop's index variable aliases the list elements. That is,
+modifying an element of a list returned by L<C<sort>|/sort SUBNAME LIST>
+(for example, in a C<foreach>, L<C<map>|/map BLOCK LIST> or
+L<C<grep>|/grep BLOCK LIST>)
actually modifies the element in the original list. This is usually
something to be avoided when writing clear code.
Perl 5.6 and earlier used a quicksort algorithm to implement sort.
-That algorithm was not stable, so I<could> go quadratic. (A I<stable> sort
+That algorithm was not stable and I<could> go quadratic. (A I<stable> sort
preserves the input order of elements that compare equal. Although
quicksort's run time is O(NlogN) when averaged over all arrays of
length N, the time can be O(N**2), I<quadratic> behavior, for some
inputs.) In 5.7, the quicksort implementation was replaced with
a stable mergesort algorithm whose worst-case behavior is O(NlogN).
But benchmarks indicated that for some inputs, on some platforms,
-the original quicksort was faster. 5.8 has a sort pragma for
+the original quicksort was faster. 5.8 has a L<sort> pragma for
limited control of the sort. Its rather blunt control of the
underlying algorithm may not persist into future Perls, but the
ability to characterize the input or output in implementation
-independent ways quite probably will. See L<the sort pragma|sort>.
+independent ways quite probably will.
Examples:
# sort lexically
- @articles = sort @files;
+ my @articles = sort @files;
# same thing, but with explicit sort routine
- @articles = sort {$a cmp $b} @files;
+ my @articles = sort {$a cmp $b} @files;
# now case-insensitively
- @articles = sort {fc($a) cmp fc($b)} @files;
+ my @articles = sort {fc($a) cmp fc($b)} @files;
# same thing in reversed order
- @articles = sort {$b cmp $a} @files;
+ my @articles = sort {$b cmp $a} @files;
# sort numerically ascending
- @articles = sort {$a <=> $b} @files;
+ my @articles = sort {$a <=> $b} @files;
# sort numerically descending
- @articles = sort {$b <=> $a} @files;
+ my @articles = sort {$b <=> $a} @files;
# this sorts the %age hash by value instead of key
# using an in-line function
- @eldest = sort { $age{$b} <=> $age{$a} } keys %age;
+ my @eldest = sort { $age{$b} <=> $age{$a} } keys %age;
# sort using explicit subroutine name
sub byage {
$age{$a} <=> $age{$b}; # presuming numeric
}
- @sortedclass = sort byage @class;
+ my @sortedclass = sort byage @class;
sub backwards { $b cmp $a }
- @harry = qw(dog cat x Cain Abel);
- @george = qw(gone chased yz Punished Axed);
+ my @harry = qw(dog cat x Cain Abel);
+ my @george = qw(gone chased yz Punished Axed);
print sort @harry;
# prints AbelCaincatdogx
print sort backwards @harry;
# same thing, but much more efficiently;
# we'll build auxiliary indices instead
# for speed
- my @nums = @caps = ();
+ my (@nums, @caps);
for (@old) {
push @nums, ( /=(\d+)/ ? $1 : undef );
push @caps, fc($_);
];
# same thing, but without any temps
- @new = map { $_->[0] }
+ my @new = map { $_->[0] }
sort { $b->[1] <=> $a->[1]
||
$a->[2] cmp $b->[2]
# using a prototype allows you to use any comparison subroutine
# as a sort subroutine (including other package's subroutines)
- package other;
+ package Other;
sub backwards ($$) { $_[1] cmp $_[0]; } # $a and $b are
- # not set here
+ # not set here
package main;
- @new = sort other::backwards @old;
+ my @new = sort Other::backwards @old;
# guarantee stability, regardless of algorithm
use sort 'stable';
- @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
+ my @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
# force use of mergesort (not portable outside Perl 5.8)
use sort '_mergesort'; # note discouraging _
- @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
+ my @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
Warning: syntactical care is required when sorting the list returned from
a function. If you want to sort the list returned by the function call
C<find_records(@key)>, you can use:
- @contact = sort { $a cmp $b } find_records @key;
- @contact = sort +find_records(@key);
- @contact = sort &find_records(@key);
- @contact = sort(find_records(@key));
+ my @contact = sort { $a cmp $b } find_records @key;
+ my @contact = sort +find_records(@key);
+ my @contact = sort &find_records(@key);
+ my @contact = sort(find_records(@key));
-If instead you want to sort the array @key with the comparison routine
+If instead you want to sort the array C<@key> with the comparison routine
C<find_records()> then you can use:
- @contact = sort { find_records() } @key;
- @contact = sort find_records(@key);
- @contact = sort(find_records @key);
- @contact = sort(find_records (@key));
+ my @contact = sort { find_records() } @key;
+ my @contact = sort find_records(@key);
+ my @contact = sort(find_records @key);
+ my @contact = sort(find_records (@key));
-If you're using strict, you I<must not> declare $a
-and $b as lexicals. They are package globals. That means
+You I<must not> declare C<$a>
+and C<$b> as lexicals. They are package globals. That means
that if you're in the C<main> package and type
- @articles = sort {$b <=> $a} @files;
+ my @articles = sort {$b <=> $a} @files;
then C<$a> and C<$b> are C<$main::a> and C<$main::b> (or C<$::a> and C<$::b>),
but if you're in the C<FooPack> package, it's the same as typing
- @articles = sort {$FooPack::b <=> $FooPack::a} @files;
+ my @articles = sort {$FooPack::b <=> $FooPack::a} @files;
The comparison function is required to behave. If it returns
inconsistent results (sometimes saying C<$x[1]> is less than C<$x[2]> and
sometimes saying the opposite, for example) the results are not
well-defined.
-Because C<< <=> >> returns C<undef> when either operand is C<NaN>
-(not-a-number), be careful when sorting with a
+Because C<< <=> >> returns L<C<undef>|/undef EXPR> when either operand
+is C<NaN> (not-a-number), be careful when sorting with a
comparison function like C<< $a <=> $b >> any lists that might contain a
C<NaN>. The following example takes advantage that C<NaN != NaN> to
eliminate any C<NaN>s from the input list.
- @result = sort { $a <=> $b } grep { $_ == $_ } @input;
+ my @result = sort { $a <=> $b } grep { $_ == $_ } @input;
-=item splice ARRAY or EXPR,OFFSET,LENGTH,LIST
+=item splice ARRAY,OFFSET,LENGTH,LIST
X<splice>
-=item splice ARRAY or EXPR,OFFSET,LENGTH
+=item splice ARRAY,OFFSET,LENGTH
-=item splice ARRAY or EXPR,OFFSET
+=item splice ARRAY,OFFSET
-=item splice ARRAY or EXPR
+=item splice ARRAY
=for Pod::Functions add or remove elements anywhere in an array
Removes the elements designated by OFFSET and LENGTH from an array, and
replaces them with the elements of LIST, if any. In list context,
returns the elements removed from the array. In scalar context,
-returns the last element removed, or C<undef> if no elements are
+returns the last element removed, or L<C<undef>|/undef EXPR> if no
+elements are
removed. The array grows or shrinks as necessary.
If OFFSET is negative then it starts that far from the end of the array.
If LENGTH is omitted, removes everything from OFFSET onward.
unshift(@a,$x,$y) splice(@a,0,0,$x,$y)
$a[$i] = $y splice(@a,$i,1,$y)
-C<splice> can be used, for example, to implement n-ary queue processing:
+L<C<splice>|/splice ARRAY,OFFSET,LENGTH,LIST> can be used, for example,
+to implement n-ary queue processing:
sub nary_print {
my $n = shift;
# d -- e -- f
# g -- h
-Starting with Perl 5.14, C<splice> can take scalar EXPR, which must hold a
-reference to an unblessed array. The argument will be dereferenced
-automatically. This aspect of C<splice> is considered highly experimental.
-The exact behaviour may change in a future version of Perl.
-
-To avoid confusing would-be users of your code who are running earlier
-versions of Perl with mysterious syntax errors, put this sort of thing at
-the top of your file to signal that your code will work I<only> on Perls of
-a recent vintage:
-
- use 5.014; # so push/pop/etc work on scalars (experimental)
+Starting with Perl 5.14, an experimental feature allowed
+L<C<splice>|/splice ARRAY,OFFSET,LENGTH,LIST> to take a
+scalar expression. This experiment has been deemed unsuccessful, and was
+removed as of Perl 5.24.
=item split /PATTERN/,EXPR,LIMIT
X<split>
Splits the string EXPR into a list of strings and returns the
list in list context, or the size of the list in scalar context.
-If only PATTERN is given, EXPR defaults to C<$_>.
+If only PATTERN is given, EXPR defaults to L<C<$_>|perlvar/$_>.
Anything in EXPR that matches PATTERN is taken to be a separator
that separates the EXPR into substrings (called "I<fields>") that
If PATTERN matches the empty string, the EXPR is split at the match
position (between characters). As an example, the following:
- print join(':', split('b', 'abc')), "\n";
+ print join(':', split(/b/, 'abc')), "\n";
-uses the 'b' in 'abc' as a separator to produce the output 'a:c'.
+uses the C<b> in C<'abc'> as a separator to produce the output C<a:c>.
However, this:
- print join(':', split('', 'abc')), "\n";
+ print join(':', split(//, 'abc')), "\n";
uses empty string matches as separators to produce the output
-'a:b:c'; thus, the empty string may be used to split EXPR into a
+C<a:b:c>; thus, the empty string may be used to split EXPR into a
list of its component characters.
-As a special case for C<split>, the empty pattern given in
-L<match operator|perlop/"m/PATTERN/msixpodualgc"> syntax (C<//>) specifically matches the empty string, which is contrary to its usual
+As a special case for L<C<split>|/split E<sol>PATTERNE<sol>,EXPR,LIMIT>,
+the empty pattern given in
+L<match operator|perlop/"m/PATTERN/msixpodualngc"> syntax (C<//>)
+specifically matches the empty string, which is contrary to its usual
interpretation as the last successful match.
If PATTERN is C</^/>, then it is treated as if it used the
L<multiline modifier|perlreref/OPERATORS> (C</^/m>), since it
isn't much use otherwise.
-As another special case, C<split> emulates the default behavior of the
-command line tool B<awk> when the PATTERN is either omitted or a I<literal
-string> composed of a single space character (such as S<C<' '>> or
+As another special case,
+L<C<split>|/split E<sol>PATTERNE<sol>,EXPR,LIMIT> emulates the default
+behavior of the
+command line tool B<awk> when the PATTERN is either omitted or a
+string composed of a single space character (such as S<C<' '>> or
S<C<"\x20">>, but not e.g. S<C</ />>). In this case, any leading
whitespace in EXPR is removed before splitting occurs, and the PATTERN is
instead treated as if it were C</\s+/>; in particular, this means that
the pattern S<C</ />> instead of the string S<C<" ">>, thereby allowing
only a single space character to be a separator. In earlier Perls this
special case was restricted to the use of a plain S<C<" ">> as the
-pattern argument to split, in Perl 5.18.0 and later this special case is
-triggered by any expression which evaluates as the simple string S<C<" ">>.
+pattern argument to split; in Perl 5.18.0 and later this special case is
+triggered by any expression which evaluates to the simple string S<C<" ">>.
If omitted, PATTERN defaults to a single space, S<C<" ">>, triggering
the previously described I<awk> emulation.
print join(':', split(//, 'abc', 1)), "\n";
-produces the output 'abc', and this:
+produces the output C<abc>, and this:
print join(':', split(//, 'abc', 2)), "\n";
-produces the output 'a:bc', and each of these:
+produces the output C<a:bc>, and each of these:
print join(':', split(//, 'abc', 3)), "\n";
print join(':', split(//, 'abc', 4)), "\n";
-produces the output 'a:b:c'.
+produces the output C<a:b:c>.
If LIMIT is negative, it is treated as if it were instead arbitrarily
large; as many fields as possible are produced.
preserved); if all fields are empty, then all fields are considered to
be trailing (and are thus stripped in this case). Thus, the following:
- print join(':', split(',', 'a,b,c,,,')), "\n";
+ print join(':', split(/,/, 'a,b,c,,,')), "\n";
-produces the output 'a:b:c', but the following:
+produces the output C<a:b:c>, but the following:
- print join(':', split(',', 'a,b,c,,,', -1)), "\n";
+ print join(':', split(/,/, 'a,b,c,,,', -1)), "\n";
-produces the output 'a:b:c:::'.
+produces the output C<a:b:c:::>.
In time-critical applications, it is worthwhile to avoid splitting
into more fields than necessary. Thus, when assigning to a list,
were one larger than the number of variables in the list; for the
following, LIMIT is implicitly 3:
- ($login, $passwd) = split(/:/);
+ my ($login, $passwd) = split(/:/);
Note that splitting an EXPR that evaluates to the empty string always
produces zero fields, regardless of the LIMIT specified.
print join(':', split(/ /, ' abc')), "\n";
-produces the output ':abc'. However, a zero-width match at the
+produces the output C<:abc>. However, a zero-width match at the
beginning of EXPR never produces an empty field, so that:
print join(':', split(//, ' abc'));
-produces the output S<' :a:b:c'> (rather than S<': :a:b:c'>).
+produces the output S<C< :a:b:c>> (rather than S<C<: :a:b:c>>).
An empty trailing field, on the other hand, is produced when there is a
match at the end of EXPR, regardless of the length of the match
print join(':', split(//, ' abc', -1)), "\n";
-produces the output S<' :a:b:c:'>.
+produces the output S<C< :a:b:c:>>.
If the PATTERN contains
L<capturing groups|perlretut/Grouping things and hierarchical matching>,
then for each separator, an additional field is produced for each substring
captured by a group (in the order in which the groups are specified,
as per L<backreferences|perlretut/Backreferences>); if any group does not
-match, then it captures the C<undef> value instead of a substring. Also,
+match, then it captures the L<C<undef>|/undef EXPR> value instead of a
+substring. Also,
note that any such additional field is produced whenever there is a
separator (that is, whenever a split occurs), and such an additional field
does B<not> count towards the LIMIT. Consider the following expressions
=for Pod::Functions formatted print into a string
-Returns a string formatted by the usual C<printf> conventions of the C
-library function C<sprintf>. See below for more details
-and see L<sprintf(3)> or L<printf(3)> on your system for an explanation of
-the general principles.
+Returns a string formatted by the usual
+L<C<printf>|/printf FILEHANDLE FORMAT, LIST> conventions of the C
+library function L<C<sprintf>|/sprintf FORMAT, LIST>. See below for
+more details and see L<sprintf(3)> or L<printf(3)> on your system for an
+explanation of the general principles.
For example:
# Format number with up to 8 leading zeroes
- $result = sprintf("%08d", $number);
+ my $result = sprintf("%08d", $number);
# Round number to 3 digits after decimal point
- $rounded = sprintf("%.3f", $number);
+ my $rounded = sprintf("%.3f", $number);
-Perl does its own C<sprintf> formatting: it emulates the C
-function sprintf(3), but doesn't use it except for floating-point
-numbers, and even then only standard modifiers are allowed.
-Non-standard extensions in your local sprintf(3) are
+Perl does its own L<C<sprintf>|/sprintf FORMAT, LIST> formatting: it
+emulates the C
+function L<sprintf(3)>, but doesn't use it except for floating-point
+numbers, and even then only standard modifiers are allowed.
+Non-standard extensions in your local L<sprintf(3)> are
therefore unavailable from Perl.
-Unlike C<printf>, C<sprintf> does not do what you probably mean when you
-pass it an array as your first argument.
+Unlike L<C<printf>|/printf FILEHANDLE FORMAT, LIST>,
+L<C<sprintf>|/sprintf FORMAT, LIST> does not do what you probably mean
+when you pass it an array as your first argument.
The array is given scalar context,
and instead of using the 0th element of the array as the format, Perl will
use the count of elements in the array as the format, which is almost never
useful.
-Perl's C<sprintf> permits the following universally-known conversions:
+Perl's L<C<sprintf>|/sprintf FORMAT, LIST> permits the following
+universally-known conversions:
%% a percent sign
%c a character with the given number
For example:
printf '<% d>', 12; # prints "< 12>"
+ printf '<% d>', 0; # prints "< 0>"
+ printf '<% d>', -12; # prints "<-12>"
printf '<%+d>', 12; # prints "<+12>"
+ printf '<%+d>', 0; # prints "<+0>"
+ printf '<%+d>', -12; # prints "<-12>"
printf '<%6s>', 12; # prints "< 12>"
printf '<%-6s>', 12; # prints "<12 >"
printf '<%06s>', 12; # prints "<000012>"
printf '<%#B>', 12; # prints "<0B1100>"
When a space and a plus sign are given as the flags at once,
-a plus sign is used to prefix a positive number.
+the space is ignored.
printf '<%+ d>', 12; # prints "<+12>"
printf '<% +d>', 12; # prints "<+12>"
printf '<%e>', 10; # prints "<1.000000e+01>"
printf '<%.1e>', 10; # prints "<1.0e+01>"
-For "g" and "G", this specifies the maximum number of digits to show,
-including those prior to the decimal point and those after it; for
-example:
+For "g" and "G", this specifies the maximum number of significant digits to
+show; for example:
# These examples are subject to system-specific variation.
printf '<%g>', 1; # prints "<1>"
printf '<%.2g>', 100.01; # prints "<1e+02>"
printf '<%.5g>', 100.01; # prints "<100.01>"
printf '<%.4g>', 100.01; # prints "<100>"
+ printf '<%.1g>', 0.0111; # prints "<0.01>"
+ printf '<%.2g>', 0.0111; # prints "<0.011>"
+ printf '<%.3g>', 0.0111; # prints "<0.0111>"
For integer conversions, specifying a precision implies that the
output of the number itself should be zero-padded to this width,
printf '<%.5s>', "truncated"; # prints "<trunc>"
printf '<%10.5s>', "truncated"; # prints "< trunc>"
-You can also get the precision from the next argument using C<.*>:
+You can also get the precision from the next argument using C<.*>, or from a
+specified argument (e.g., with C<.*2$>):
printf '<%.6x>', 1; # prints "<000001>"
printf '<%.*x>', 6, 1; # prints "<000001>"
+ printf '<%.*2$x>', 1, 6; # prints "<000001>"
+
+ printf '<%6.*2$x>', 1, 4; # prints "< 0001>"
+
If a precision obtained through C<*> is negative, it counts
as having no precision at all.
printf '<%.*d>', 0, 0; # prints "<>"
printf '<%.*d>', -1, 0; # prints "<0>"
-You cannot currently get the precision from a specified number,
-but it is intended that this will be possible in the future, for
-example using C<.*2$>:
-
- printf '<%.*2$x>', 1, 6; # INVALID, but in future will print
- # "<000001>"
-
=item size
For numeric conversions, you can specify the size to interpret the
As of 5.14, none of these raises an exception if they are not supported on
your platform. However, if warnings are enabled, a warning of the
-C<printf> warning class is issued on an unsupported conversion flag.
-Should you instead prefer an exception, do this:
+L<C<printf>|warnings> warning class is issued on an unsupported
+conversion flag. Should you instead prefer an exception, do this:
use warnings FATAL => "printf";
=item order of arguments
-Normally, sprintf() takes the next unused argument as the value to
+Normally, L<C<sprintf>|/sprintf FORMAT, LIST> takes the next unused
+argument as the value to
format for each format specification. If the format specification
uses C<*> to require additional arguments, these are consumed from
the argument list in the order they appear in the format
Here are some more examples; be aware that when using an explicit
index, the C<$> may need escaping:
- printf "%2\$d %d\n", 12, 34; # will print "34 12\n"
- printf "%2\$d %d %d\n", 12, 34; # will print "34 12 34\n"
- printf "%3\$d %d %d\n", 12, 34, 56; # will print "56 12 34\n"
- printf "%2\$*3\$d %d\n", 12, 34, 3; # will print " 34 12\n"
+ printf "%2\$d %d\n", 12, 34; # will print "34 12\n"
+ printf "%2\$d %d %d\n", 12, 34; # will print "34 12 34\n"
+ printf "%3\$d %d %d\n", 12, 34, 56; # will print "56 12 34\n"
+ printf "%2\$*3\$d %d\n", 12, 34, 3; # will print " 34 12\n"
+ printf "%*1\$.*f\n", 4, 5, 10; # will print "5.0000\n"
=back
-If C<use locale> (including C<use locale 'not_characters'>) is in effect
-and POSIX::setlocale() has been called,
+If L<C<use locale>|locale> (including C<use locale ':not_characters'>)
+is in effect and L<C<POSIX::setlocale>|POSIX/C<setlocale>> has been
+called,
the character used for the decimal separator in formatted floating-point
numbers is affected by the C<LC_NUMERIC> locale. See L<perllocale>
and L<POSIX>.
=for Pod::Functions square root function
Return the positive square root of EXPR. If EXPR is omitted, uses
-C<$_>. Works only for non-negative operands unless you've
-loaded the C<Math::Complex> module.
+L<C<$_>|perlvar/$_>. Works only for non-negative operands unless you've
+loaded the L<C<Math::Complex>|Math::Complex> module.
use Math::Complex;
print sqrt(-4); # prints 2i
=for Pod::Functions seed the random number generator
-Sets and returns the random number seed for the C<rand> operator.
+Sets and returns the random number seed for the L<C<rand>|/rand EXPR>
+operator.
-The point of the function is to "seed" the C<rand> function so that C<rand>
-can produce a different sequence each time you run your program. When
-called with a parameter, C<srand> uses that for the seed; otherwise it
+The point of the function is to "seed" the L<C<rand>|/rand EXPR>
+function so that L<C<rand>|/rand EXPR> can produce a different sequence
+each time you run your program. When called with a parameter,
+L<C<srand>|/srand EXPR> uses that for the seed; otherwise it
(semi-)randomly chooses a seed. In either case, starting with Perl 5.14,
it returns the seed. To signal that your code will work I<only> on Perls
of a recent vintage:
use 5.014; # so srand returns the seed
-If C<srand()> is not called explicitly, it is called implicitly without a
-parameter at the first use of the C<rand> operator.
-However, there are a few situations where programs are likely to
-want to call C<srand>. One is for generating predictable results, generally for
-testing or debugging. There, you use C<srand($seed)>, with the same C<$seed>
-each time. Another case is that you may want to call C<srand()>
-after a C<fork()> to avoid child processes sharing the same seed value as the
-parent (and consequently each other).
+If L<C<srand>|/srand EXPR> is not called explicitly, it is called
+implicitly without a parameter at the first use of the
+L<C<rand>|/rand EXPR> operator. However, there are a few situations
+where programs are likely to want to call L<C<srand>|/srand EXPR>. One
+is for generating predictable results, generally for testing or
+debugging. There, you use C<srand($seed)>, with the same C<$seed> each
+time. Another case is that you may want to call L<C<srand>|/srand EXPR>
+after a L<C<fork>|/fork> to avoid child processes sharing the same seed
+value as the parent (and consequently each other).
Do B<not> call C<srand()> (i.e., without an argument) more than once per
process. The internal state of the random number generator should
contain more entropy than can be provided by any seed, so calling
-C<srand()> again actually I<loses> randomness.
+L<C<srand>|/srand EXPR> again actually I<loses> randomness.
-Most implementations of C<srand> take an integer and will silently
+Most implementations of L<C<srand>|/srand EXPR> take an integer and will
+silently
truncate decimal numbers. This means C<srand(42)> will usually
produce the same results as C<srand(42.1)>. To be safe, always pass
-C<srand> an integer.
+L<C<srand>|/srand EXPR> an integer.
A typical use of the returned seed is for a test program which has too many
combinations to test comprehensively in the time available to it each run. It
can test a random subset each time, and should there be a failure, log the seed
used for that run so that it can later be used to reproduce the same results.
-B<C<rand()> is not cryptographically secure. You should not rely
+B<L<C<rand>|/rand EXPR> is not cryptographically secure. You should not rely
on it in security-sensitive situations.> As of this writing, a
number of third-party CPAN modules offer random number generators
intended by their authors to be cryptographically secure,
=for Pod::Functions get a file's status information
Returns a 13-element list giving the status info for a file, either
-the file opened via FILEHANDLE or DIRHANDLE, or named by EXPR. If EXPR is
-omitted, it stats C<$_> (not C<_>!). Returns the empty list if C<stat> fails. Typically
+the file opened via FILEHANDLE or DIRHANDLE, or named by EXPR. If EXPR is
+omitted, it stats L<C<$_>|perlvar/$_> (not C<_>!). Returns the empty
+list if L<C<stat>|/stat FILEHANDLE> fails. Typically
used as follows:
- ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
- $atime,$mtime,$ctime,$blksize,$blocks)
+ my ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
+ $atime,$mtime,$ctime,$blksize,$blocks)
= stat($filename);
Not all fields are supported on all filesystem types. Here are the
ctime field is non-portable. In particular, you cannot expect it to be a
"creation time"; see L<perlport/"Files and Filesystems"> for details.
-If C<stat> is passed the special filehandle consisting of an underline, no
-stat is done, but the current contents of the stat structure from the
-last C<stat>, C<lstat>, or filetest are returned. Example:
+If L<C<stat>|/stat FILEHANDLE> is passed the special filehandle
+consisting of an underline, no stat is done, but the current contents of
+the stat structure from the last L<C<stat>|/stat FILEHANDLE>,
+L<C<lstat>|/lstat FILEHANDLE>, or filetest are returned. Example:
if (-x $file && (($d) = stat(_)) && $d < 0) {
print "$file is executable NFS file\n";
should mask off the file type portion and (s)printf using a C<"%o">
if you want to see the real permissions.
- $mode = (stat($filename))[2];
+ my $mode = (stat($filename))[2];
printf "Permissions are %04o\n", $mode & 07777;
-In scalar context, C<stat> returns a boolean value indicating success
+In scalar context, L<C<stat>|/stat FILEHANDLE> returns a boolean value
+indicating success
or failure, and, if successful, sets the information associated with
the special filehandle C<_>.
The L<File::stat> module provides a convenient, by-name access mechanism:
use File::stat;
- $sb = stat($filename);
+ my $sb = stat($filename);
printf "File is %s, size is %s, perm %04o, mtime %s\n",
$filename, $sb->size, $sb->mode & 07777,
scalar localtime $sb->mtime;
You can import symbolic mode constants (C<S_IF*>) and functions
-(C<S_IS*>) from the Fcntl module:
+(C<S_IS*>) from the L<Fcntl> module:
use Fcntl ':mode';
- $mode = (stat($filename))[2];
+ my $mode = (stat($filename))[2];
- $user_rwx = ($mode & S_IRWXU) >> 6;
- $group_read = ($mode & S_IRGRP) >> 3;
- $other_execute = $mode & S_IXOTH;
+ my $user_rwx = ($mode & S_IRWXU) >> 6;
+ my $group_read = ($mode & S_IRGRP) >> 3;
+ my $other_execute = $mode & S_IXOTH;
printf "Permissions are %04o\n", S_IMODE($mode), "\n";
- $is_setuid = $mode & S_ISUID;
- $is_directory = S_ISDIR($mode);
+ my $is_setuid = $mode & S_ISUID;
+ my $is_directory = S_ISDIR($mode);
You could write the last two using the C<-u> and C<-d> operators.
Commonly available C<S_IF*> constants are:
S_ISENFMT($mode) S_ISWHT($mode)
-See your native chmod(2) and stat(2) documentation for more details
+See your native L<chmod(2)> and L<stat(2)> documentation for more details
about the C<S_*> constants. To get status info for a symbolic link
-instead of the target file behind the link, use the C<lstat> function.
+instead of the target file behind the link, use the
+L<C<lstat>|/lstat FILEHANDLE> function.
Portability issues: L<perlport/stat>.
=for Pod::Functions +state declare and assign a persistent lexical variable
-C<state> declares a lexically scoped variable, just like C<my>.
+L<C<state>|/state VARLIST> declares a lexically scoped variable, just
+like L<C<my>|/my VARLIST>.
However, those variables will never be reinitialized, contrary to
lexical variables that are reinitialized each time their enclosing block
is entered.
See L<perlsub/"Persistent Private Variables"> for details.
If more than one variable is listed, the list must be placed in
-parentheses. With a parenthesised list, C<undef> can be used as a
+parentheses. With a parenthesised list, L<C<undef>|/undef EXPR> can be
+used as a
dummy placeholder. However, since initialization of state variables in
list context is currently not possible this would serve no purpose.
-C<state> variables are enabled only when the C<use feature "state"> pragma
-is in effect, unless the keyword is written as C<CORE::state>.
-See also L<feature>.
+L<C<state>|/state VARLIST> is available only if the
+L<C<"state"> feature|feature/The 'state' feature> is enabled or if it is
+prefixed with C<CORE::>. The
+L<C<"state"> feature|feature/The 'state' feature> is enabled
+automatically with a C<use v5.10> (or higher) declaration in the current
+scope.
+
=item study SCALAR
X<study>
=item study
-=for Pod::Functions optimize input data for repeated searches
-
-Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of
-doing many pattern matches on the string before it is next modified.
-This may or may not save time, depending on the nature and number of
-patterns you are searching and the distribution of character
-frequencies in the string to be searched; you probably want to compare
-run times with and without it to see which is faster. Those loops
-that scan for many short constant strings (including the constant
-parts of more complex patterns) will benefit most.
-(The way C<study> works is this: a linked list of every
-character in the string to be searched is made, so we know, for
-example, where all the C<'k'> characters are. From each search string,
-the rarest character is selected, based on some static frequency tables
-constructed from some C programs and English text. Only those places
-that contain this "rarest" character are examined.)
-
-For example, here is a loop that inserts index producing entries
-before any line containing a certain pattern:
+=for Pod::Functions no-op, formerly optimized input data for repeated searches
- while (<>) {
- study;
- print ".IX foo\n" if /\bfoo\b/;
- print ".IX bar\n" if /\bbar\b/;
- print ".IX blurfl\n" if /\bblurfl\b/;
- # ...
- print;
- }
+At this time, C<study> does nothing. This may change in the future.
+
+Prior to Perl version 5.16, it would create an inverted index of all characters
+that occurred in the given SCALAR (or L<C<$_>|perlvar/$_> if unspecified). When
+matching a pattern, the rarest character from the pattern would be looked up in
+this index. Rarity was based on some static frequency tables constructed from
+some C programs and English text.
-In searching for C</\bfoo\b/>, only locations in C<$_> that contain C<f>
-will be looked at, because C<f> is rarer than C<o>. In general, this is
-a big win except in pathological cases. The only question is whether
-it saves you more time than it took to build the linked list in the
-first place.
-
-Note that if you have to look for strings that you don't know till
-runtime, you can build an entire loop as a string and C<eval> that to
-avoid recompiling all your patterns all the time. Together with
-undefining C<$/> to input entire files as one record, this can be quite
-fast, often faster than specialized programs like fgrep(1). The following
-scans a list of files (C<@files>) for a list of words (C<@words>), and prints
-out the names of those files that contain a match:
-
- $search = 'while (<>) { study;';
- foreach $word (@words) {
- $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
- }
- $search .= "}";
- @ARGV = @files;
- undef $/;
- eval $search; # this screams
- $/ = "\n"; # put back to normal input delimiter
- foreach $file (sort keys(%seen)) {
- print $file, "\n";
- }
=item sub NAME BLOCK
X<sub>
=for Pod::Functions +current_sub the current subroutine, or C<undef> if not in a subroutine
A special token that returns a reference to the current subroutine, or
-C<undef> outside of a subroutine.
+L<C<undef>|/undef EXPR> outside of a subroutine.
-The behaviour of C<__SUB__> within a regex code block (such as C</(?{...})/>)
-is subject to change.
+The behaviour of L<C<__SUB__>|/__SUB__> within a regex code block (such
+as C</(?{...})/>) is subject to change.
-This token is only available under C<use v5.16> or the "current_sub"
-feature. See L<feature>.
+This token is only available under C<use v5.16> or the
+L<C<"current_sub"> feature|feature/The 'current_sub' feature>.
+See L<feature>.
=item substr EXPR,OFFSET,LENGTH,REPLACEMENT
X<substr> X<substring> X<mid> X<left> X<right>
my $tail = substr $s, -4; # tree
my $z = substr $s, -4, 2; # tr
-You can use the substr() function as an lvalue, in which case EXPR
+You can use the L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT>
+function as an lvalue, in which case EXPR
must itself be an lvalue. If you assign something shorter than LENGTH,
the string will shrink, and if you assign something longer than LENGTH,
the string will grow to accommodate it. To keep the string the same
-length, you may need to pad or chop your value using C<sprintf>.
+length, you may need to pad or chop your value using
+L<C<sprintf>|/sprintf FORMAT, LIST>.
If OFFSET and LENGTH specify a substring that is partly outside the
string, only the part within the string is returned. If the substring
-is beyond either end of the string, substr() returns the undefined
+is beyond either end of the string,
+L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT> returns the undefined
value and produces a warning. When used as an lvalue, specifying a
substring that is entirely outside the string raises an exception.
Here's an example showing the behavior for boundary cases:
my $oops = substr $name, 7; # returns undef, with warning
substr($name, 7) = 'gap'; # raises an exception
-An alternative to using substr() as an lvalue is to specify the
+An alternative to using
+L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT> as an lvalue is to
+specify the
replacement string as the 4th argument. This allows you to replace
parts of the EXPR and return what was there before in one operation,
-just as you can with splice().
+just as you can with
+L<C<splice>|/splice ARRAY,OFFSET,LENGTH,LIST>.
my $s = "The black cat climbed the green tree";
my $z = substr $s, 14, 7, "jumped from"; # climbed
# $s is now "The black cat jumped from the green tree"
-Note that the lvalue returned by the three-argument version of substr() acts as
+Note that the lvalue returned by the three-argument version of
+L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT> acts as
a 'magic bullet'; each time it is assigned to, it remembers which part
of the original string is being modified; for example:
- $x = '1234';
+ my $x = '1234';
for (substr($x,1,2)) {
$_ = 'a'; print $x,"\n"; # prints 1a4
$_ = 'xyz'; print $x,"\n"; # prints 1xyz4
With negative offsets, it remembers its position from the end of the string
when the target string is modified:
- $x = '1234';
+ my $x = '1234';
for (substr($x, -3, 2)) {
$_ = 'a'; print $x,"\n"; # prints 1a4, as above
$x = 'abcdefg';
symbolic links, raises an exception. To check for that,
use eval:
- $symlink_exists = eval { symlink("",""); 1 };
+ my $symlink_exists = eval { symlink("",""); 1 };
Portability issues: L<perlport/symlink>.
an int. If not, the pointer to the string value is passed. You are
responsible to make sure a string is pre-extended long enough to
receive any result that might be written into a string. You can't use a
-string literal (or other read-only string) as an argument to C<syscall>
-because Perl has to assume that any string pointer might be written
-through. If your
+string literal (or other read-only string) as an argument to
+L<C<syscall>|/syscall NUMBER, LIST> because Perl has to assume that any
+string pointer might be written through. If your
integer arguments are not literals and have never been interpreted in a
numeric context, you may need to add C<0> to them to force them to look
-like numbers. This emulates the C<syswrite> function (or vice versa):
+like numbers. This emulates the
+L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET> function (or
+vice versa):
require 'syscall.ph'; # may need to run h2ph
- $s = "hi there\n";
- syscall(&SYS_write, fileno(STDOUT), $s, length $s);
+ my $s = "hi there\n";
+ syscall(SYS_write(), fileno(STDOUT), $s, length $s);
Note that Perl supports passing of up to only 14 arguments to your syscall,
which in practice should (usually) suffice.
Syscall returns whatever value returned by the system call it calls.
-If the system call fails, C<syscall> returns C<-1> and sets C<$!> (errno).
+If the system call fails, L<C<syscall>|/syscall NUMBER, LIST> returns
+C<-1> and sets L<C<$!>|perlvar/$!> (errno).
Note that some system calls I<can> legitimately return C<-1>. The proper
-way to handle such calls is to assign C<$!=0> before the call, then
-check the value of C<$!> if C<syscall> returns C<-1>.
+way to handle such calls is to assign C<$! = 0> before the call, then
+check the value of L<C<$!>|perlvar/$!> if
+L<C<syscall>|/syscall NUMBER, LIST> returns C<-1>.
-There's a problem with C<syscall(&SYS_pipe)>: it returns the file
+There's a problem with C<syscall(SYS_pipe())>: it returns the file
number of the read end of the pipe it creates, but there is no way
to retrieve the file number of the other end. You can avoid this
-problem by using C<pipe> instead.
+problem by using L<C<pipe>|/pipe READHANDLE,WRITEHANDLE> instead.
Portability issues: L<perlport/syscall>.
Opens the file whose filename is given by FILENAME, and associates it with
FILEHANDLE. If FILEHANDLE is an expression, its value is used as the real
filehandle wanted; an undefined scalar will be suitably autovivified. This
-function calls the underlying operating system's I<open>(2) function with the
+function calls the underlying operating system's L<open(2)> function with the
parameters FILENAME, MODE, and PERMS.
+Returns true on success and L<C<undef>|/undef EXPR> otherwise.
+
The possible values and flag bits of the MODE parameter are
-system-dependent; they are available via the standard module C<Fcntl>. See
-the documentation of your operating system's I<open>(2) syscall to see
+system-dependent; they are available via the standard module
+L<C<Fcntl>|Fcntl>. See the documentation of your operating system's
+L<open(2)> syscall to see
which values and flag bits are available. You may combine several flags
using the C<|>-operator.
OS/390 and on the Macintosh; you probably don't want to
use them in new code.
-If the file named by FILENAME does not exist and the C<open> call creates
+If the file named by FILENAME does not exist and the
+L<C<open>|/open FILEHANDLE,EXPR> call creates
it (typically because MODE includes the C<O_CREAT> flag), then the value of
PERMS specifies the permissions of the newly created file. If you omit
-the PERMS argument to C<sysopen>, Perl uses the octal value C<0666>.
+the PERMS argument to L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE>,
+Perl uses the octal value C<0666>.
These permission values need to be in octal, and are modified by your
-process's current C<umask>.
+process's current L<C<umask>|/umask EXPR>.
X<O_CREAT>
In many systems the C<O_EXCL> flag is available for opening files in
exclusive mode. This is B<not> locking: exclusiveness means here that
-if the file already exists, sysopen() fails. C<O_EXCL> may not work
+if the file already exists,
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> fails. C<O_EXCL> may
+not work
on network filesystems, and has no effect unless the C<O_CREAT> flag
is set as well. Setting C<O_CREAT|O_EXCL> prevents the file from
being opened if it is a symbolic link. It does not protect against
C<O_TRUNC> with C<O_RDONLY> is undefined.
X<O_TRUNC>
-You should seldom if ever use C<0644> as argument to C<sysopen>, because
+You should seldom if ever use C<0644> as argument to
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE>, because
that takes away the user's option to have a more permissive umask.
-Better to omit it. See the perlfunc(1) entry on C<umask> for more
-on this.
+Better to omit it. See L<C<umask>|/umask EXPR> for more on this.
-Note that C<sysopen> depends on the fdopen() C library function.
-On many Unix systems, fdopen() is known to fail when file descriptors
-exceed a certain value, typically 255. If you need more file
-descriptors than that, consider using the POSIX::open() function.
+Note that under Perls older than 5.8.0,
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> depends on the
+L<fdopen(3)> C library function. On many Unix systems, L<fdopen(3)> is known
+to fail when file descriptors exceed a certain value, typically 255. If
+you need more file descriptors than that, consider using the
+L<C<POSIX::open>|POSIX/C<open>> function. For Perls 5.8.0 and later,
+PerlIO is (most often) the default.
See L<perlopentut> for a kinder, gentler explanation of opening files.
=for Pod::Functions fixed-length unbuffered input from a filehandle
Attempts to read LENGTH bytes of data into variable SCALAR from the
-specified FILEHANDLE, using the read(2). It bypasses
-buffered IO, so mixing this with other kinds of reads, C<print>,
-C<write>, C<seek>, C<tell>, or C<eof> can cause confusion because the
-perlio or stdio layers usually buffers data. Returns the number of
+specified FILEHANDLE, using L<read(2)>. It bypasses
+buffered IO, so mixing this with other kinds of reads,
+L<C<print>|/print FILEHANDLE LIST>, L<C<write>|/write FILEHANDLE>,
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<tell>|/tell FILEHANDLE>, or L<C<eof>|/eof FILEHANDLE> can cause
+confusion because the
+perlio or stdio layers usually buffer data. Returns the number of
bytes actually read, C<0> at end of file, or undef if there was an
-error (in the latter case C<$!> is also set). SCALAR will be grown or
+error (in the latter case L<C<$!>|perlvar/$!> is also set). SCALAR will
+be grown or
shrunk so that the last byte actually read is the last byte of the
scalar after the read.
results in the string being padded to the required size with C<"\0">
bytes before the result of the read is appended.
-There is no syseof() function, which is ok, since eof() doesn't work
-well on device files (like ttys) anyway. Use sysread() and check
-for a return value for 0 to decide whether you're done.
+There is no syseof() function, which is ok, since
+L<C<eof>|/eof FILEHANDLE> doesn't work well on device files (like ttys)
+anyway. Use L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET> and
+check for a return value for 0 to decide whether you're done.
-Note that if the filehandle has been marked as C<:utf8> Unicode
+Note that if the filehandle has been marked as C<:utf8>, Unicode
characters are read instead of bytes (the LENGTH, OFFSET, and the
-return value of sysread() are in Unicode characters).
-The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer.
-See L</binmode>, L</open>, and the C<open> pragma, L<open>.
+return value of L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>
+are in Unicode characters). The C<:encoding(...)> layer implicitly
+introduces the C<:utf8> layer. See
+L<C<binmode>|/binmode FILEHANDLE, LAYER>,
+L<C<open>|/open FILEHANDLE,EXPR>, and the L<open> pragma.
=item sysseek FILEHANDLE,POSITION,WHENCE
X<sysseek> X<lseek>
=for Pod::Functions +5.004 position I/O pointer on handle used with sysread and syswrite
-Sets FILEHANDLE's system position in bytes using lseek(2). FILEHANDLE may
+Sets FILEHANDLE's system position I<in bytes> using L<lseek(2)>. FILEHANDLE may
be an expression whose value gives the name of the filehandle. The values
for WHENCE are C<0> to set the new position to POSITION; C<1> to set the it
to the current position plus POSITION; and C<2> to set it to EOF plus
POSITION, typically negative.
-Note the I<in bytes>: even if the filehandle has been set to operate
-on characters (for example by using the C<:encoding(utf8)> I/O layer),
-tell() will return byte offsets, not character offsets (because
-implementing that would render sysseek() unacceptably slow).
-
-sysseek() bypasses normal buffered IO, so mixing it with reads other
-than C<sysread> (for example C<< <> >> or read()) C<print>, C<write>,
-C<seek>, C<tell>, or C<eof> may cause confusion.
+Note the emphasis on bytes: even if the filehandle has been set to operate
+on characters (for example using the C<:encoding(utf8)> I/O layer), the
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<tell>|/tell FILEHANDLE>, and
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE>
+family of functions use byte offsets, not character offsets,
+because seeking to a character offset would be very slow in a UTF-8 file.
+
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE> bypasses normal
+buffered IO, so mixing it with reads other than
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET> (for example
+L<C<readline>|/readline EXPR> or
+L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET>),
+L<C<print>|/print FILEHANDLE LIST>, L<C<write>|/write FILEHANDLE>,
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<tell>|/tell FILEHANDLE>, or L<C<eof>|/eof FILEHANDLE> may cause
+confusion.
For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>,
and C<SEEK_END> (start of the file, current position, end of the file)
-from the Fcntl module. Use of the constants is also more portable
+from the L<Fcntl> module. Use of the constants is also more portable
than relying on 0, 1, and 2. For example to define a "systell" function:
use Fcntl 'SEEK_CUR';
sub systell { sysseek($_[0], 0, SEEK_CUR) }
Returns the new position, or the undefined value on failure. A position
-of zero is returned as the string C<"0 but true">; thus C<sysseek> returns
+of zero is returned as the string C<"0 but true">; thus
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE> returns
true on success and false on failure, yet you can still easily determine
the new position.
=for Pod::Functions run a separate program
-Does exactly the same thing as C<exec LIST>, except that a fork is
+Does exactly the same thing as L<C<exec>|/exec LIST>, except that a fork is
done first and the parent process waits for the child process to
exit. Note that argument processing varies depending on the
number of arguments. If there is more than one argument in LIST,
Perl will attempt to flush all files opened for
output before any operation that may do a fork, but this may not be
supported on some platforms (see L<perlport>). To be safe, you may need
-to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method
-of C<IO::Handle> on any open handles.
+to set L<C<$E<verbar>>|perlvar/$E<verbar>> (C<$AUTOFLUSH> in L<English>)
+or call the C<autoflush> method of L<C<IO::Handle>|IO::Handle/METHODS>
+on any open handles.
The return value is the exit status of the program as returned by the
-C<wait> call. To get the actual exit value, shift right by eight (see
-below). See also L</exec>. This is I<not> what you want to use to capture
-the output from a command; for that you should use merely backticks or
-C<qx//>, as described in L<perlop/"`STRING`">. Return value of -1
-indicates a failure to start the program or an error of the wait(2) system
-call (inspect $! for the reason).
-
-If you'd like to make C<system> (and many other bits of Perl) die on error,
-have a look at the L<autodie> pragma.
-
-Like C<exec>, C<system> allows you to lie to a program about its name if
-you use the C<system PROGRAM LIST> syntax. Again, see L</exec>.
+L<C<wait>|/wait> call. To get the actual exit value, shift right by
+eight (see below). See also L<C<exec>|/exec LIST>. This is I<not> what
+you want to use to capture the output from a command; for that you
+should use merely backticks or
+L<C<qxE<sol>E<sol>>|/qxE<sol>STRINGE<sol>>, as described in
+L<perlop/"`STRING`">. Return value of -1 indicates a failure to start
+the program or an error of the L<wait(2)> system call (inspect
+L<C<$!>|perlvar/$!> for the reason).
+
+If you'd like to make L<C<system>|/system LIST> (and many other bits of
+Perl) die on error, have a look at the L<autodie> pragma.
+
+Like L<C<exec>|/exec LIST>, L<C<system>|/system LIST> allows you to lie
+to a program about its name if you use the C<system PROGRAM LIST>
+syntax. Again, see L<C<exec>|/exec LIST>.
Since C<SIGINT> and C<SIGQUIT> are ignored during the execution of
-C<system>, if you expect your program to terminate on receipt of these
-signals you will need to arrange to do so yourself based on the return
-value.
+L<C<system>|/system LIST>, if you expect your program to terminate on
+receipt of these signals you will need to arrange to do so yourself
+based on the return value.
- @args = ("command", "arg1", "arg2");
+ my @args = ("command", "arg1", "arg2");
system(@args) == 0
- or die "system @args failed: $?"
+ or die "system @args failed: $?";
-If you'd like to manually inspect C<system>'s failure, you can check all
-possible failure modes by inspecting C<$?> like this:
+If you'd like to manually inspect L<C<system>|/system LIST>'s failure,
+you can check all possible failure modes by inspecting
+L<C<$?>|perlvar/$?> like this:
if ($? == -1) {
print "failed to execute: $!\n";
printf "child exited with value %d\n", $? >> 8;
}
-Alternatively, you may inspect the value of C<${^CHILD_ERROR_NATIVE}>
-with the C<W*()> calls from the POSIX module.
+Alternatively, you may inspect the value of
+L<C<${^CHILD_ERROR_NATIVE}>|perlvar/${^CHILD_ERROR_NATIVE}> with the
+L<C<W*()>|POSIX/C<WIFEXITED>> calls from the L<POSIX> module.
-When C<system>'s arguments are executed indirectly by the shell,
-results and return codes are subject to its quirks.
-See L<perlop/"`STRING`"> and L</exec> for details.
+When L<C<system>|/system LIST>'s arguments are executed indirectly by
+the shell, results and return codes are subject to its quirks.
+See L<perlop/"`STRING`"> and L<C<exec>|/exec LIST> for details.
-Since C<system> does a C<fork> and C<wait> it may affect a C<SIGCHLD>
-handler. See L<perlipc> for details.
+Since L<C<system>|/system LIST> does a L<C<fork>|/fork> and
+L<C<wait>|/wait> it may affect a C<SIGCHLD> handler. See L<perlipc> for
+details.
Portability issues: L<perlport/system>.
=for Pod::Functions fixed-length unbuffered output to a filehandle
Attempts to write LENGTH bytes of data from variable SCALAR to the
-specified FILEHANDLE, using write(2). If LENGTH is
+specified FILEHANDLE, using L<write(2)>. If LENGTH is
not specified, writes whole SCALAR. It bypasses buffered IO, so
-mixing this with reads (other than C<sysread())>, C<print>, C<write>,
-C<seek>, C<tell>, or C<eof> may cause confusion because the perlio and
-stdio layers usually buffer data. Returns the number of bytes
-actually written, or C<undef> if there was an error (in this case the
-errno variable C<$!> is also set). If the LENGTH is greater than the
+mixing this with reads (other than C<sysread)>),
+L<C<print>|/print FILEHANDLE LIST>, L<C<write>|/write FILEHANDLE>,
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<tell>|/tell FILEHANDLE>, or L<C<eof>|/eof FILEHANDLE> may cause
+confusion because the perlio and stdio layers usually buffer data.
+Returns the number of bytes actually written, or L<C<undef>|/undef EXPR>
+if there was an error (in this case the errno variable
+L<C<$!>|perlvar/$!> is also set). If the LENGTH is greater than the
data available in the SCALAR after the OFFSET, only as much data as is
available will be written.
B<WARNING>: If the filehandle is marked C<:utf8>, Unicode characters
encoded in UTF-8 are written instead of bytes, and the LENGTH, OFFSET, and
-return value of syswrite() are in (UTF8-encoded Unicode) characters.
+return value of L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET>
+are in (UTF8-encoded Unicode) characters.
The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer.
Alternately, if the handle is not marked with an encoding but you
attempt to write characters with code points over 255, raises an exception.
-See L</binmode>, L</open>, and the C<open> pragma, L<open>.
+See L<C<binmode>|/binmode FILEHANDLE, LAYER>,
+L<C<open>|/open FILEHANDLE,EXPR>, and the L<open> pragma.
=item tell FILEHANDLE
X<tell>
the actual filehandle. If FILEHANDLE is omitted, assumes the file
last read.
-Note the I<in bytes>: even if the filehandle has been set to
-operate on characters (for example by using the C<:encoding(utf8)> open
-layer), tell() will return byte offsets, not character offsets (because
-that would render seek() and tell() rather slow).
-
-The return value of tell() for the standard streams like the STDIN
-depends on the operating system: it may return -1 or something else.
-tell() on pipes, fifos, and sockets usually returns -1.
-
-There is no C<systell> function. Use C<sysseek(FH, 0, 1)> for that.
-
-Do not use tell() (or other buffered I/O operations) on a filehandle
-that has been manipulated by sysread(), syswrite(), or sysseek().
-Those functions ignore the buffering, while tell() does not.
+Note the emphasis on bytes: even if the filehandle has been set to operate
+on characters (for example using the C<:encoding(utf8)> I/O layer), the
+L<C<seek>|/seek FILEHANDLE,POSITION,WHENCE>,
+L<C<tell>|/tell FILEHANDLE>, and
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE>
+family of functions use byte offsets, not character offsets,
+because seeking to a character offset would be very slow in a UTF-8 file.
+
+The return value of L<C<tell>|/tell FILEHANDLE> for the standard streams
+like the STDIN depends on the operating system: it may return -1 or
+something else. L<C<tell>|/tell FILEHANDLE> on pipes, fifos, and
+sockets usually returns -1.
+
+There is no C<systell> function. Use
+L<C<sysseek($fh, 0, 1)>|/sysseek FILEHANDLE,POSITION,WHENCE> for that.
+
+Do not use L<C<tell>|/tell FILEHANDLE> (or other buffered I/O
+operations) on a filehandle that has been manipulated by
+L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>,
+L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET>, or
+L<C<sysseek>|/sysseek FILEHANDLE,POSITION,WHENCE>. Those functions
+ignore the buffering, while L<C<tell>|/tell FILEHANDLE> does not.
=item telldir DIRHANDLE
X<telldir>
=for Pod::Functions get current seekpointer on a directory handle
-Returns the current position of the C<readdir> routines on DIRHANDLE.
-Value may be given to C<seekdir> to access a particular location in a
-directory. C<telldir> has the same caveats about possible directory
-compaction as the corresponding system library routine.
+Returns the current position of the L<C<readdir>|/readdir DIRHANDLE>
+routines on DIRHANDLE. Value may be given to
+L<C<seekdir>|/seekdir DIRHANDLE,POS> to access a particular location in
+a directory. L<C<telldir>|/telldir DIRHANDLE> has the same caveats
+about possible directory compaction as the corresponding system library
+routine.
=item tie VARIABLE,CLASSNAME,LIST
X<tie>
appropriate constructor
method of the class (meaning C<TIESCALAR>, C<TIEHANDLE>, C<TIEARRAY>,
or C<TIEHASH>). Typically these are arguments such as might be passed
-to the C<dbm_open()> function of C. The object returned by the
-constructor is also returned by the C<tie> function, which would be useful
+to the L<dbm_open(3)> function of C. The object returned by the
+constructor is also returned by the
+L<C<tie>|/tie VARIABLE,CLASSNAME,LIST> function, which would be useful
if you want to access other methods in CLASSNAME.
-Note that functions such as C<keys> and C<values> may return huge lists
-when used on large objects, like DBM files. You may prefer to use the
-C<each> function to iterate over such. Example:
+Note that functions such as L<C<keys>|/keys HASH> and
+L<C<values>|/values HASH> may return huge lists when used on large
+objects, like DBM files. You may prefer to use the L<C<each>|/each
+HASH> function to iterate over such. Example:
# print out history file offsets
use NDBM_File;
- tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
- while (($key,$val) = each %HIST) {
- print $key, ' = ', unpack('L',$val), "\n";
+ tie(my %HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
+ while (my ($key,$val) = each %HIST) {
+ print $key, ' = ', unpack('L', $val), "\n";
}
- untie(%HIST);
A class implementing a hash should have the following methods:
Not all methods indicated above need be implemented. See L<perltie>,
L<Tie::Hash>, L<Tie::Array>, L<Tie::Scalar>, and L<Tie::Handle>.
-Unlike C<dbmopen>, the C<tie> function will not C<use> or C<require> a module
-for you; you need to do that explicitly yourself. See L<DB_File>
-or the F<Config> module for interesting C<tie> implementations.
+Unlike L<C<dbmopen>|/dbmopen HASH,DBNAME,MASK>, the
+L<C<tie>|/tie VARIABLE,CLASSNAME,LIST> function will not
+L<C<use>|/use Module VERSION LIST> or L<C<require>|/require VERSION> a
+module for you; you need to do that explicitly yourself. See L<DB_File>
+or the L<Config> module for interesting
+L<C<tie>|/tie VARIABLE,CLASSNAME,LIST> implementations.
-For further details see L<perltie>, L<"tied VARIABLE">.
+For further details see L<perltie>, L<C<tied>|/tied VARIABLE>.
=item tied VARIABLE
X<tied>
=for Pod::Functions get a reference to the object underlying a tied variable
Returns a reference to the object underlying VARIABLE (the same value
-that was originally returned by the C<tie> call that bound the variable
+that was originally returned by the
+L<C<tie>|/tie VARIABLE,CLASSNAME,LIST> call that bound the variable
to a package.) Returns the undefined value if VARIABLE isn't tied to a
package.
=for Pod::Functions return number of seconds since 1970
Returns the number of non-leap seconds since whatever time the system
-considers to be the epoch, suitable for feeding to C<gmtime> and
-C<localtime>. On most systems the epoch is 00:00:00 UTC, January 1, 1970;
+considers to be the epoch, suitable for feeding to
+L<C<gmtime>|/gmtime EXPR> and L<C<localtime>|/localtime EXPR>. On most
+systems the epoch is 00:00:00 UTC, January 1, 1970;
a prominent exception being Mac OS Classic which uses 00:00:00, January 1,
1904 in the current local time zone for its epoch.
For measuring time in better granularity than one second, use the
L<Time::HiRes> module from Perl 5.8 onwards (or from CPAN before then), or,
-if you have gettimeofday(2), you may be able to use the C<syscall>
-interface of Perl. See L<perlfaq8> for details.
+if you have L<gettimeofday(2)>, you may be able to use the
+L<C<syscall>|/syscall NUMBER, LIST> interface of Perl. See L<perlfaq8>
+for details.
For date and time processing look at the many related modules on CPAN.
For a comprehensive date and time representation look at the
Returns a four-element list giving the user and system times in
seconds for this process and any exited children of this process.
- ($user,$system,$cuser,$csystem) = times;
+ my ($user,$system,$cuser,$csystem) = times;
-In scalar context, C<times> returns C<$user>.
+In scalar context, L<C<times>|/times> returns C<$user>.
Children's times are only included for terminated children.
=for Pod::Functions transliterate a string
-The transliteration operator. Same as C<y///>. See
+The transliteration operator. Same as
+L<C<yE<sol>E<sol>E<sol>>|/yE<sol>E<sol>E<sol>>. See
L<perlop/"Quote-Like Operators">.
=item truncate FILEHANDLE,LENGTH
Truncates the file opened on FILEHANDLE, or named by EXPR, to the
specified length. Raises an exception if truncate isn't implemented
-on your system. Returns true if successful, C<undef> on error.
+on your system. Returns true if successful, L<C<undef>|/undef EXPR> on
+error.
The behavior is undefined if LENGTH is greater than the length of the
file.
The position in the file of FILEHANDLE is left unchanged. You may want to
-call L<seek|/"seek FILEHANDLE,POSITION,WHENCE"> before writing to the file.
+call L<seek|/"seek FILEHANDLE,POSITION,WHENCE"> before writing to the
+file.
Portability issues: L<perlport/truncate>.
Returns an uppercased version of EXPR. This is the internal function
implementing the C<\U> escape in double-quoted strings.
It does not attempt to do titlecase mapping on initial letters. See
-L</ucfirst> for that.
+L<C<ucfirst>|/ucfirst EXPR> for that.
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
-This function behaves the same way under various pragma, such as in a locale,
-as L</lc> does.
+This function behaves the same way under various pragmas, such as in a locale,
+as L<C<lc>|/lc EXPR> does.
=item ucfirst EXPR
X<ucfirst> X<uppercase>
(titlecase in Unicode). This is the internal function implementing
the C<\u> escape in double-quoted strings.
-If EXPR is omitted, uses C<$_>.
+If EXPR is omitted, uses L<C<$_>|perlvar/$_>.
-This function behaves the same way under various pragma, such as in a locale,
-as L</lc> does.
+This function behaves the same way under various pragmas, such as in a locale,
+as L<C<lc>|/lc EXPR> does.
=item umask EXPR
X<umask>
The Unix permission C<rwxr-x---> is represented as three sets of three
bits, or three octal digits: C<0750> (the leading 0 indicates octal
-and isn't one of the digits). The C<umask> value is such a number
-representing disabled permissions bits. The permission (or "mode")
-values you pass C<mkdir> or C<sysopen> are modified by your umask, so
-even if you tell C<sysopen> to create a file with permissions C<0777>,
-if your umask is C<0022>, then the file will actually be created with
-permissions C<0755>. If your C<umask> were C<0027> (group can't
-write; others can't read, write, or execute), then passing
-C<sysopen> C<0666> would create a file with mode C<0640> (because
-C<0666 &~ 027> is C<0640>).
+and isn't one of the digits). The L<C<umask>|/umask EXPR> value is such
+a number representing disabled permissions bits. The permission (or
+"mode") values you pass L<C<mkdir>|/mkdir FILENAME,MASK> or
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> are modified by your
+umask, so even if you tell
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> to create a file with
+permissions C<0777>, if your umask is C<0022>, then the file will
+actually be created with permissions C<0755>. If your
+L<C<umask>|/umask EXPR> were C<0027> (group can't write; others can't
+read, write, or execute), then passing
+L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> C<0666> would create a
+file with mode C<0640> (because C<0666 &~ 027> is C<0640>).
Here's some advice: supply a creation mode of C<0666> for regular
-files (in C<sysopen>) and one of C<0777> for directories (in
-C<mkdir>) and executable files. This gives users the freedom of
+files (in L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE>) and one of
+C<0777> for directories (in L<C<mkdir>|/mkdir FILENAME,MASK>) and
+executable files. This gives users the freedom of
choice: if they want protected files, they might choose process umasks
of C<022>, C<027>, or even the particularly antisocial mask of C<077>.
Programs should rarely if ever make policy decisions better left to
the user. The exception to this is when writing files that should be
-kept private: mail files, web browser cookies, I<.rhosts> files, and
+kept private: mail files, web browser cookies, F<.rhosts> files, and
so on.
-If umask(2) is not implemented on your system and you are trying to
-restrict access for I<yourself> (i.e., C<< (EXPR & 0700) > 0 >>),
-raises an exception. If umask(2) is not implemented and you are
-not trying to restrict access for yourself, returns C<undef>.
+If L<umask(2)> is not implemented on your system and you are trying to
+restrict access for I<yourself> (i.e., C<< (EXPR & 0700) > 0 >>),
+raises an exception. If L<umask(2)> is not implemented and you are
+not trying to restrict access for yourself, returns
+L<C<undef>|/undef EXPR>.
Remember that a umask is a number, usually given in octal; it is I<not> a
-string of octal digits. See also L</oct>, if all you have is a string.
+string of octal digits. See also L<C<oct>|/oct EXPR>, if all you have
+is a string.
Portability issues: L<perlport/umask>.
scalar value, an array (using C<@>), a hash (using C<%>), a subroutine
(using C<&>), or a typeglob (using C<*>). Saying C<undef $hash{$key}>
will probably not do what you expect on most predefined variables or
-DBM list values, so don't do that; see L</delete>. Always returns the
-undefined value. You can omit the EXPR, in which case nothing is
+DBM list values, so don't do that; see L<C<delete>|/delete EXPR>.
+Always returns the undefined value.
+You can omit the EXPR, in which case nothing is
undefined, but you still get an undefined value that you could, for
instance, return from a subroutine, assign to a variable, or pass as a
parameter. Examples:
undef *xyz; # destroys $xyz, @xyz, %xyz, &xyz, etc.
return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
select undef, undef, undef, 0.25;
- ($a, $b, undef, $c) = &foo; # Ignore third value returned
+ my ($x, $y, undef, $z) = foo(); # Ignore third value returned
Note that this is a unary operator, not a list operator.
=for Pod::Functions remove one link to a file
Deletes a list of files. On success, it returns the number of files
-it successfully deleted. On failure, it returns false and sets C<$!>
-(errno):
+it successfully deleted. On failure, it returns false and sets
+L<C<$!>|perlvar/$!> (errno):
my $unlinked = unlink 'a', 'b', 'c';
unlink @goners;
unlink glob "*.bak";
-On error, C<unlink> will not tell you which files it could not remove.
+On error, L<C<unlink>|/unlink LIST> will not tell you which files it
+could not remove.
If you want to know which files you could not remove, try them one
at a time:
unlink $file or warn "Could not unlink $file: $!";
}
-Note: C<unlink> will not attempt to delete directories unless you are
+Note: L<C<unlink>|/unlink LIST> will not attempt to delete directories
+unless you are
superuser and the B<-U> flag is supplied to Perl. Even if these
conditions are met, be warned that unlinking a directory can inflict
-damage on your filesystem. Finally, using C<unlink> on directories is
-not supported on many operating systems. Use C<rmdir> instead.
+damage on your filesystem. Finally, using L<C<unlink>|/unlink LIST> on
+directories is not supported on many operating systems. Use
+L<C<rmdir>|/rmdir FILENAME> instead.
-If LIST is omitted, C<unlink> uses C<$_>.
+If LIST is omitted, L<C<unlink>|/unlink LIST> uses L<C<$_>|perlvar/$_>.
=item unpack TEMPLATE,EXPR
X<unpack>
=for Pod::Functions convert binary structure into normal perl variables
-C<unpack> does the reverse of C<pack>: it takes a string
+L<C<unpack>|/unpack TEMPLATE,EXPR> does the reverse of
+L<C<pack>|/pack TEMPLATE,LIST>: it takes a string
and expands it out into a list of values.
(In scalar context, it returns merely the first value produced.)
-If EXPR is omitted, unpacks the C<$_> string.
+If EXPR is omitted, unpacks the L<C<$_>|perlvar/$_> string.
See L<perlpacktut> for an introduction to this function.
The string is broken into chunks described by the TEMPLATE. Each chunk
is converted separately to a value. Typically, either the string is a result
-of C<pack>, or the characters of the string represent a C structure of some
-kind.
+of L<C<pack>|/pack TEMPLATE,LIST>, or the characters of the string
+represent a C structure of some kind.
-The TEMPLATE has the same format as in the C<pack> function.
+The TEMPLATE has the same format as in the
+L<C<pack>|/pack TEMPLATE,LIST> function.
Here's a subroutine that does substring:
sub substr {
- my($what,$where,$howmuch) = @_;
+ my ($what, $where, $howmuch) = @_;
unpack("x$where a$howmuch", $what);
}
sub ordinal { unpack("W",$_[0]); } # same as ord()
-In addition to fields allowed in pack(), you may prefix a field with
-a %<number> to indicate that
+In addition to fields allowed in L<C<pack>|/pack TEMPLATE,LIST>, you may
+prefix a field with a %<number> to indicate that
you want a <number>-bit checksum of the items instead of the items
-themselves. Default is a 16-bit checksum. Checksum is calculated by
+themselves. Default is a 16-bit checksum. The checksum is calculated by
summing numeric values of expanded values (for string fields the sum of
C<ord($char)> is taken; for bit fields the sum of zeroes and ones).
For example, the following
computes the same number as the System V sum program:
- $checksum = do {
+ my $checksum = do {
local $/; # slurp!
- unpack("%32W*",<>) % 65535;
+ unpack("%32W*", readline) % 65535;
};
The following efficiently counts the number of set bits in a bit vector:
- $setbits = unpack("%32b*", $selectmask);
+ my $setbits = unpack("%32b*", $selectmask);
The C<p> and C<P> formats should be used with care. Since Perl
-has no way of checking whether the value passed to C<unpack()>
+has no way of checking whether the value passed to
+L<C<unpack>|/unpack TEMPLATE,EXPR>
corresponds to a valid memory location, passing a pointer value that's
not known to be valid is likely to have disastrous consequences.
If there are more pack codes or if the repeat count of a field or a group
is larger than what the remainder of the input string allows, the result
is not well defined: the repeat count may be decreased, or
-C<unpack()> may produce empty strings or zeros, or it may raise an exception.
+L<C<unpack>|/unpack TEMPLATE,EXPR> may produce empty strings or zeros,
+or it may raise an exception.
If the input string is longer than one described by the TEMPLATE,
the remainder of that input string is ignored.
-See L</pack> for more examples and notes.
+See L<C<pack>|/pack TEMPLATE,LIST> for more examples and notes.
=item unshift ARRAY,LIST
X<unshift>
-=item unshift EXPR,LIST
-
=for Pod::Functions prepend more elements to the beginning of a list
-Does the opposite of a C<shift>. Or the opposite of a C<push>,
+Does the opposite of a L<C<shift>|/shift ARRAY>. Or the opposite of a
+L<C<push>|/push ARRAY,LIST>,
depending on how you look at it. Prepends list to the front of the
array and returns the new number of elements in the array.
unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;
Note the LIST is prepended whole, not one element at a time, so the
-prepended elements stay in the same order. Use C<reverse> to do the
-reverse.
-
-Starting with Perl 5.14, C<unshift> can take a scalar EXPR, which must hold
-a reference to an unblessed array. The argument will be dereferenced
-automatically. This aspect of C<unshift> is considered highly
-experimental. The exact behaviour may change in a future version of Perl.
+prepended elements stay in the same order. Use
+L<C<reverse>|/reverse LIST> to do the reverse.
-To avoid confusing would-be users of your code who are running earlier
-versions of Perl with mysterious syntax errors, put this sort of thing at
-the top of your file to signal that your code will work I<only> on Perls of
-a recent vintage:
-
- use 5.014; # so push/pop/etc work on scalars (experimental)
+Starting with Perl 5.14, an experimental feature allowed
+L<C<unshift>|/unshift ARRAY,LIST> to take
+a scalar expression. This experiment has been deemed unsuccessful, and was
+removed as of Perl 5.24.
=item untie VARIABLE
X<untie>
The importation can be made conditional by using the L<if> module.
In the peculiar C<use VERSION> form, VERSION may be either a positive
-decimal fraction such as 5.006, which will be compared to C<$]>, or a v-string
-of the form v5.6.1, which will be compared to C<$^V> (aka $PERL_VERSION). An
+decimal fraction such as 5.006, which will be compared to
+L<C<$]>|perlvar/$]>, or a v-string of the form v5.6.1, which will be
+compared to L<C<$^V>|perlvar/$^V> (aka $PERL_VERSION). An
exception is raised if VERSION is greater than the version of the
current Perl interpreter; Perl will not attempt to parse the rest of the
-file. Compare with L</require>, which can do a similar check at run time.
+file. Compare with L<C<require>|/require VERSION>, which can do a
+similar check at run time.
Symmetrically, C<no VERSION> allows you to specify that you want a version
of Perl older than the specified one.
use 5.006_001; # ditto; preferred for backwards compatibility
This is often useful if you need to check the current Perl version before
-C<use>ing library modules that won't work with older versions of Perl.
+L<C<use>|/use Module VERSION LIST>ing library modules that won't work
+with older versions of Perl.
(We try not to do this more than we have to.)
C<use VERSION> also lexically enables all features available in the requested
-version as defined by the C<feature> pragma, disabling any features
+version as defined by the L<feature> pragma, disabling any features
not in the requested version's feature bundle. See L<feature>.
Similarly, if the specified Perl version is greater than or equal to
5.12.0, strictures are enabled lexically as
-with C<use strict>. Any explicit use of
+with L<C<use strict>|strict>. Any explicit use of
C<use strict> or C<no strict> overrides C<use VERSION>, even if it comes
before it. Later use of C<use VERSION>
will override all behavior of a previous
load the F<feature.pm> or F<strict.pm>
files.
-The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The
-C<require> makes sure the module is loaded into memory if it hasn't been
-yet. The C<import> is not a builtin; it's just an ordinary static method
+The C<BEGIN> forces the L<C<require>|/require VERSION> and
+L<C<import>|/import LIST> to happen at compile time. The
+L<C<require>|/require VERSION> makes sure the module is loaded into
+memory if it hasn't been yet. The L<C<import>|/import LIST> is not a
+builtin; it's just an ordinary static method
call into the C<Module> package to tell the module to import the list of
features back into the current package. The module can implement its
-C<import> method any way it likes, though most modules just choose to
-derive their C<import> method via inheritance from the C<Exporter> class that
-is defined in the C<Exporter> module. See L<Exporter>. If no C<import>
-method can be found then the call is skipped, even if there is an AUTOLOAD
-method.
-
-If you do not want to call the package's C<import> method (for instance,
+L<C<import>|/import LIST> method any way it likes, though most modules
+just choose to derive their L<C<import>|/import LIST> method via
+inheritance from the C<Exporter> class that is defined in the
+L<C<Exporter>|Exporter> module. See L<Exporter>. If no
+L<C<import>|/import LIST> method can be found, then the call is skipped,
+even if there is an AUTOLOAD method.
+
+If you do not want to call the package's L<C<import>|/import LIST>
+method (for instance,
to stop your namespace from being altered), explicitly supply the empty list:
use Module ();
BEGIN { require Module }
If the VERSION argument is present between Module and LIST, then the
-C<use> will call the VERSION method in class Module with the given
-version as an argument. The default VERSION method, inherited from
-the UNIVERSAL class, croaks if the given version is larger than the
-value of the variable C<$Module::VERSION>.
+L<C<use>|/use Module VERSION LIST> will call the C<VERSION> method in
+class Module with the given version as an argument:
+
+ use Module 12.34;
+
+is equivalent to:
+
+ BEGIN { require Module; Module->VERSION(12.34) }
-Again, there is a distinction between omitting LIST (C<import> called
-with no arguments) and an explicit empty LIST C<()> (C<import> not
-called). Note that there is no comma after VERSION!
+The L<default C<VERSION> method|UNIVERSAL/C<VERSION ( [ REQUIRE ] )>>,
+inherited from the L<C<UNIVERSAL>|UNIVERSAL> class, croaks if the given
+version is larger than the value of the variable C<$Module::VERSION>.
+
+Again, there is a distinction between omitting LIST (L<C<import>|/import
+LIST> called with no arguments) and an explicit empty LIST C<()>
+(L<C<import>|/import LIST> not called). Note that there is no comma
+after VERSION!
Because this is a wide-open interface, pragmas (compiler directives)
-are also implemented this way. Currently implemented pragmas are:
+are also implemented this way. Some of the currently implemented
+pragmas are:
use constant;
use diagnostics;
use sort qw(stable _quicksort _mergesort);
Some of these pseudo-modules import semantics into the current
-block scope (like C<strict> or C<integer>, unlike ordinary modules,
-which import symbols into the current package (which are effective
-through the end of the file).
-
-Because C<use> takes effect at compile time, it doesn't respect the
-ordinary flow control of the code being compiled. In particular, putting
-a C<use> inside the false branch of a conditional doesn't prevent it
-from being processed. If a module or pragma only needs to be loaded
+block scope (like L<C<strict>|strict> or L<C<integer>|integer>, unlike
+ordinary modules, which import symbols into the current package (which
+are effective through the end of the file).
+
+Because L<C<use>|/use Module VERSION LIST> takes effect at compile time,
+it doesn't respect the ordinary flow control of the code being compiled.
+In particular, putting a L<C<use>|/use Module VERSION LIST> inside the
+false branch of a conditional doesn't prevent it
+from being processed. If a module or pragma only needs to be loaded
conditionally, this can be done using the L<if> pragma:
use if $] < 5.008, "utf8";
use if WANT_WARNINGS, warnings => qw(all);
-There's a corresponding C<no> declaration that unimports meanings imported
-by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import>.
-It behaves just as C<import> does with VERSION, an omitted or empty LIST,
+There's a corresponding L<C<no>|/no MODULE VERSION LIST> declaration
+that unimports meanings imported by L<C<use>|/use Module VERSION LIST>,
+i.e., it calls C<< Module->unimport(LIST) >> instead of
+L<C<import>|/import LIST>. It behaves just as L<C<import>|/import LIST>
+does with VERSION, an omitted or empty LIST,
or no unimport method being found.
no integer;
no strict 'refs';
no warnings;
-Care should be taken when using the C<no VERSION> form of C<no>. It is
+Care should be taken when using the C<no VERSION> form of L<C<no>|/no
+MODULE VERSION LIST>. It is
I<only> meant to be used to assert that the running Perl is of a earlier
version than its argument and I<not> to undo the feature-enabling side effects
of C<use VERSION>.
See L<perlmodlib> for a list of standard modules and pragmas. See L<perlrun>
-for the C<-M> and C<-m> command-line options to Perl that give C<use>
-functionality from the command-line.
+for the C<-M> and C<-m> command-line options to Perl that give
+L<C<use>|/use Module VERSION LIST> functionality from the command-line.
=item utime LIST
X<utime>
and modification times, in that order. Returns the number of files
successfully changed. The inode change time of each file is set
to the current time. For example, this code has the same effect as the
-Unix
touch(1) command when the files I<already exist> and belong to
+Unix
L<touch(1)> command when the files I<already exist> and belong to
the user running the program:
#!/usr/bin/perl
- $atime = $mtime = time;
+ my $atime = my $mtime = time;
utime $atime, $mtime, @ARGV;
-Since Perl 5.8.0, if the first two elements of the list are C<undef>,
-the utime(2) syscall from your C library is called with a null second
+Since Perl 5.8.0, if the first two elements of the list are
+L<C<undef>|/undef EXPR>,
+the L<utime(2)> syscall from your C library is called with a null second
argument. On most systems, this will set the file's access and
modification times to the current time (i.e., equivalent to the example
above) and will work even on files you don't own provided you have write
permission:
- for $file (@ARGV) {
- utime(undef, undef, $file)
- || warn "couldn't touch $file: $!";
- }
+ for my $file (@ARGV) {
+ utime(undef, undef, $file)
+ || warn "Couldn't touch $file: $!";
+ }
Under NFS this will use the time of the NFS server, not the time of
the local machine. If there is a time synchronization problem, the
NFS server and local machine will have different times. The Unix
-touch(1) command will in fact normally use this form instead of the
+L<touch(1)> command will in fact normally use this form instead of the
one shown in the first example.
-Passing only one of the first two elements as C<undef> is
-equivalent to passing a 0 and will not have the effect
-described when both are C<undef>. This also triggers an
+Passing only one of the first two elements as L<C<undef>|/undef EXPR> is
+equivalent to passing a 0 and will not have the effect described when
+both are L<C<undef>|/undef EXPR>. This also triggers an
uninitialized warning.
-On systems that support futimes(2), you may pass filehandles among the
-files. On systems that don't support futimes(2), passing filehandles raises
+On systems that support L<futimes(2)>, you may pass filehandles among the
+files. On systems that don't support L<futimes(2)>, passing filehandles raises
an exception. Filehandles must be passed as globs or glob references to be
recognized; barewords are considered filenames.
=item values ARRAY
-=item values EXPR
-
=for Pod::Functions return a list of the values in a hash
In list context, returns a list consisting of all the values of the named
order is specific to a given hash; the exact same series of operations
on two hashes may result in a different order for each hash. Any insertion
into the hash may change the order, as will any deletion, with the exception
-that the most recent key returned by C<each> or C<keys> may be deleted
-without changing the order. So long as a given hash is unmodified you may
-rely on C<keys>, C<values> and C<each> to repeatedly return the same order
+that the most recent key returned by L<C<each>|/each HASH> or
+L<C<keys>|/keys HASH> may be deleted without changing the order. So
+long as a given hash is unmodified you may rely on
+L<C<keys>|/keys HASH>, L<C<values>|/values HASH> and
+L<C<each>|/each HASH> to repeatedly return the same order
as each other. See L<perlsec/"Algorithmic Complexity Attacks"> for
details on why hash order is randomized. Aside from the guarantees
provided here the exact details of Perl's hash algorithm and the hash
may behave differently to Perl's hashes with respect to changes in order on
insertion and deletion of items.
-As a side effect, calling values() resets the HASH or ARRAY's internal
-iterator, see L</each>. (In particular, calling values() in void context
-resets the iterator with no other overhead. Apart from resetting the
-iterator, C<values @array> in list context is the same as plain C<@array>.
+As a side effect, calling L<C<values>|/values HASH> resets the HASH or
+ARRAY's internal iterator, see L<C<each>|/each HASH>. (In particular,
+calling L<C<values>|/values HASH> in void context resets the iterator
+with no other overhead. Apart from resetting the iterator,
+C<values @array> in list context is the same as plain C<@array>.
(We recommend that you use void context C<keys @array> for this, but
reasoned that taking C<values @array> out would require more
documentation than leaving it in.)
for (values %hash) { s/foo/bar/g } # modifies %hash values
for (@hash{keys %hash}) { s/foo/bar/g } # same
-Starting with Perl 5.14, C<values> can take a scalar EXPR, which must hold
-a reference to an unblessed hash or array. The argument will be
-dereferenced automatically. This aspect of C<values> is considered highly
-experimental. The exact behaviour may change in a future version of Perl.
-
- for (values $hashref) { ... }
- for (values $obj->get_arrayref) { ... }
+Starting with Perl 5.14, an experimental feature allowed
+L<C<values>|/values HASH> to take a
+scalar expression. This experiment has been deemed unsuccessful, and was
+removed as of Perl 5.24.
To avoid confusing would-be users of your code who are running earlier
versions of Perl with mysterious syntax errors, put this sort of thing at
a recent vintage:
use 5.012; # so keys/values/each work on arrays
- use 5.014; # so keys/values/each work on scalars (experimental)
-See also C<keys>, C<each>, and C<sort>.
+See also L<C<keys>|/keys HASH>, L<C<each>|/each HASH>, and
+L<C<sort>|/sort SUBNAME LIST>.
=item vec EXPR,OFFSET,BITS
X<vec> X<bit> X<bit vector>
If BITS is 16 or more, bytes of the input string are grouped into chunks
of size BITS/8, and each group is converted to a number as with
-pack()/unpack() with big-endian formats C<n>/C<N> (and analogously
-for BITS==64). See L<"pack"> for details.
+L<C<pack>|/pack TEMPLATE,LIST>/L<C<unpack>|/unpack TEMPLATE,EXPR> with
+big-endian formats C<n>/C<N> (and analogously for BITS==64). See
+L<C<pack>|/pack TEMPLATE,LIST> for details.
If bits is 4 or less, the string is broken into bytes, then the bits
of each byte are broken into 8/BITS groups. Bits of a byte are
breaking the single input byte C<chr(0x36)> into two groups gives a list
C<(0x6, 0x3)>; breaking it into 4 groups gives C<(0x2, 0x1, 0x3, 0x0)>.
-C<vec> may also be assigned to, in which case parentheses are needed
+L<C<vec>|/vec EXPR,OFFSET,BITS> may also be assigned to, in which case
+parentheses are needed
to give the expression the correct precedence as in
vec($image, $max_x * $x + $y, 8) = 3;
to try to write off the beginning of the string (i.e., negative OFFSET).
If the string happens to be encoded as UTF-8 internally (and thus has
-the UTF8 flag set), this is ignored by C<vec>, and it operates on the
+the UTF8 flag set), this is ignored by L<C<vec>|/vec EXPR,OFFSET,BITS>,
+and it operates on the
internal byte string, not the conceptual character string, even if you
-only have characters with values less than 256.
+only have characters with values less than 256.
-Strings created with C<vec> can also be manipulated with the logical
+Strings created with L<C<vec>|/vec EXPR,OFFSET,BITS> can also be
+manipulated with the logical
operators C<|>, C<&>, C<^>, and C<~>. These operators will assume a bit
vector operation is desired when both operands are strings.
See L<perlop/"Bitwise String Operators">.
To transform a bit vector into a string or list of 0's and 1's, use these:
- $bits = unpack("b*", $vector);
- @bits = split(//, unpack("b*", $vector));
+ my $bits = unpack("b*", $vector);
+ my @bits = split(//, unpack("b*", $vector));
If you know the exact length in bits, it can be used in place of the C<*>.
.
__END__
-Regardless of the machine architecture on which it runs, the
+Regardless of the machine architecture on which it runs, the
example above should print the following table:
0 1 2 3
=for Pod::Functions wait for any child process to die
-Behaves like wait(2) on your system: it waits for a child
+Behaves like L<wait(2)> on your system: it waits for a child
process to terminate and returns the pid of the deceased process, or
-C<-1> if there are no child processes. The status is returned in C<$?>
-and C<${^CHILD_ERROR_NATIVE}>.
+C<-1> if there are no child processes. The status is returned in
+L<C<$?>|perlvar/$?> and
+L<C<${^CHILD_ERROR_NATIVE}>|perlvar/${^CHILD_ERROR_NATIVE}>.
Note that a return value of C<-1> could mean that child processes are
being automatically reaped, as described in L<perlipc>.
-If you use wait in your handler for $SIG{CHLD} it may accidentally for the
-child created by qx() or system(). See L<perlipc> for details.
+If you use L<C<wait>|/wait> in your handler for
+L<C<$SIG{CHLD}>|perlvar/%SIG>, it may accidentally wait for the child
+created by L<C<qx>|/qxE<sol>STRINGE<sol>> or L<C<system>|/system LIST>.
+See L<perlipc> for details.
Portability issues: L<perlport/wait>.
=for Pod::Functions wait for a particular child process to die
Waits for a particular child process to terminate and returns the pid of
-the deceased process, or C<-1> if there is no such child process. On some
-systems, a value of 0 indicates that there are processes still running.
-The status is returned in C<$?> and C<${^CHILD_ERROR_NATIVE}>. If you say
+the deceased process, or C<-1> if there is no such child process. A
+non-blocking wait (with L<WNOHANG|POSIX/C<WNOHANG>> in FLAGS) can return 0 if
+there are child processes matching PID but none have terminated yet.
+The status is returned in L<C<$?>|perlvar/$?> and
+L<C<${^CHILD_ERROR_NATIVE}>|perlvar/${^CHILD_ERROR_NATIVE}>.
+
+A PID of C<0> indicates to wait for any child process whose process group ID is
+equal to that of the current process. A PID of less than C<-1> indicates to
+wait for any child process whose process group ID is equal to -PID. A PID of
+C<-1> indicates to wait for any child process.
+
+If you say
use POSIX ":sys_wait_h";
- #...
+
+ my $kid;
do {
$kid = waitpid(-1, WNOHANG);
} while $kid > 0;
-then you can do a non-blocking wait for all pending zombie processes.
+or
+
+ 1 while waitpid(-1, WNOHANG) > 0;
+
+then you can do a non-blocking wait for all pending zombie processes (see
+L<POSIX/WAIT>).
Non-blocking wait is available on machines supporting either the
-waitpid(2) or wait4(2) syscalls. However, waiting for a particular
+L<waitpid(2)> or L<wait4(2)> syscalls. However, waiting for a particular
pid with FLAGS of C<0> is implemented everywhere. (Perl emulates the
system call by remembering the status values of processes that have
exited but have not been harvested by the Perl script yet.)
=for Pod::Functions get void vs scalar vs list context of current subroutine call
Returns true if the context of the currently executing subroutine or
-C<eval> is looking for a list value. Returns false if the context is
+L<C<eval>|/eval EXPR> is looking for a list value. Returns false if the
+context is
looking for a scalar. Returns the undefined value if the context is
looking for no value (void context).
my @a = complex_calculation();
return wantarray ? @a : "@a";
-C<wantarray()>'s result is unspecified in the top level of a file,
+L<C<wantarray>|/wantarray>'s result is unspecified in the top level of a file,
in a C<BEGIN>, C<UNITCHECK>, C<CHECK>, C<INIT> or C<END> block, or
in a C<DESTROY> method.
=for Pod::Functions print debugging info
Prints the value of LIST to STDERR. If the last element of LIST does
-not end in a newline, it appends the same file/line number text as C<die>
-does.
+not end in a newline, it appends the same file/line number text as
+L<C<die>|/die LIST> does.
-If the output is empty and C<$@> already contains a value (typically from a
-previous eval) that value is used after appending C<"\t...caught">
-to C<$@>. This is useful for staying almost, but not entirely similar to
-C<die>.
+If the output is empty and L<C<$@>|perlvar/$@> already contains a value
+(typically from a previous eval) that value is used after appending
+C<"\t...caught"> to L<C<$@>|perlvar/$@>. This is useful for staying
+almost, but not entirely similar to L<C<die>|/die LIST>.
-If C<$@> is empty then the string C<"Warning: Something's wrong"> is used.
+If L<C<$@>|perlvar/$@> is empty, then the string
+C<"Warning: Something's wrong"> is used.
-No message is printed if there is a C<$SIG{__WARN__}> handler
+No message is printed if there is a L<C<$SIG{__WARN__}>|perlvar/%SIG>
+handler
installed. It is the handler's responsibility to deal with the message
-as it sees fit (like, for instance, converting it into a C<die>). Most
+as it sees fit (like, for instance, converting it into a
+L<C<die>|/die LIST>). Most
handlers must therefore arrange to actually display the
-warnings that they are not prepared to deal with, by calling C<warn>
+warnings that they are not prepared to deal with, by calling
+L<C<warn>|/warn LIST>
again in the handler. Note that this is quite safe and will not
produce an endless loop, since C<__WARN__> hooks are not called from
inside one.
You will find this behavior is slightly different from that of
-C<$SIG{__DIE__}> handlers (which don't suppress the error text, but can
-instead call C<die> again to change it).
+L<C<$SIG{__DIE__}>|perlvar/%SIG> handlers (which don't suppress the
+error text, but can instead call L<C<die>|/die LIST> again to change
+it).
Using a C<__WARN__> handler provides a powerful way to silence all
warnings (even the so-called mandatory ones). An example:
# run-time warnings enabled after here
warn "\$foo is alive and $foo!"; # does show up
-See L<perlvar> for details on setting C<%SIG> entries and for more
-examples. See the Carp module for other kinds of warnings using its
-carp() and cluck() functions.
+See L<perlvar> for details on setting L<C<%SIG>|perlvar/%SIG> entries
+and for more
+examples. See the L<Carp> module for other kinds of warnings using its
+C<carp> and C<cluck> functions.
=item write FILEHANDLE
X<write>
Writes a formatted record (possibly multi-line) to the specified FILEHANDLE,
using the format associated with that file. By default the format for
a file is the one having the same name as the filehandle, but the
-format for the current output channel (see the C<select> function) may be set
-explicitly by assigning the name of the format to the C<$~> variable.
+format for the current output channel (see the
+L<C<select>|/select FILEHANDLE> function) may be set explicitly by
+assigning the name of the format to the L<C<$~>|perlvar/$~> variable.
Top of form processing is handled automatically: if there is insufficient
room on the current page for the formatted record, the page is advanced by
writing a form feed and a special top-of-page
format is used to format the new
page header before the record is written. By default, the top-of-page
-format is the name of the filehandle with "_TOP" appended, or "top"
+format is the name of the filehandle with C<_TOP> appended, or C<top>
in the current package if the former does not exist. This would be a
problem with autovivified filehandles, but it may be dynamically set to the
-format of your choice by assigning the name to the C<$^> variable while
-that filehandle is selected. The number of lines remaining on the current
-page is in variable C<$->, which can be set to C<0> to force a new page.
+format of your choice by assigning the name to the L<C<$^>|perlvar/$^>
+variable while that filehandle is selected. The number of lines
+remaining on the current page is in variable L<C<$->|perlvar/$->, which
+can be set to C<0> to force a new page.
If FILEHANDLE is unspecified, output goes to the current default output
channel, which starts out as STDOUT but may be changed by the
-C<select> operator. If the FILEHANDLE is an EXPR, then the expression
+L<C<select>|/select FILEHANDLE> operator. If the FILEHANDLE is an EXPR,
+then the expression
is evaluated and the resulting string is used to look up the name of
the FILEHANDLE at run time. For more on formats, see L<perlform>.
-Note that write is I<not> the opposite of C<read>. Unfortunately.
+Note that write is I<not> the opposite of
+L<C<read>|/read FILEHANDLE,SCALAR,LENGTH,OFFSET>. Unfortunately.
=item y///
=for Pod::Functions transliterate a string
-The transliteration operator. Same as C<tr///>. See
+The transliteration operator. Same as
+L<C<trE<sol>E<sol>E<sol>>|/trE<sol>E<sol>E<sol>>. See
L<perlop/"Quote-Like Operators">.
=back
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