operators take more than one argument, while unary operators can never
take more than one argument. Thus, a comma terminates the argument of
a unary operator, but merely separates the arguments of a list
-operator. A unary operator generally provides a scalar context to its
+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
come first and list argument follow, and there can only ever
C<time() + 86_400>.
For functions that can be used in either a scalar or list context,
-nonabortive failure is generally indicated in a scalar context by
-returning the undefined value, and in a list context by returning the
+nonabortive failure is generally indicated in scalar context by
+returning the undefined value, and in list context by returning the
empty list.
Remember the following important rule: There is B<no rule> that relates
=item Functions for SCALARs or strings
X<scalar> X<string> X<character>
-C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>,
-C<length>, C<oct>, C<ord>, C<pack>, C<q//>, C<qq//>, C<reverse>,
+=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
+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>
-C<m//>, C<pos>, C<quotemeta>, C<s///>, C<split>, C<study>, C<qr//>
+=for Pod::Functions =Regexp
+
+C<m//>, C<pos>, C<qr//>, C<quotemeta>, C<s///>, C<split>, C<study>
=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>
=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>
=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>
=item Functions for real %HASHes
X<hash>
+=for Pod::Functions =HASH
+
C<delete>, C<each>, C<exists>, C<keys>, C<values>
=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<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<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
+with a C<use v5.10> (or higher) declaration in the current scope.
=item Functions for fixed-length data or records
-C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec>
+=for Pod::Functions =Binary
+
+C<pack>, C<read>, C<syscall>, C<sysread>, C<sysseek>, C<syswrite>, C<unpack>,
+C<vec>
=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>,
=item Keywords related to the control flow of your Perl program
X<control flow>
-C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<eval>, C<exit>,
-C<goto>, C<last>, C<next>, C<redo>, C<return>, C<sub>, C<wantarray>
+=for Pod::Functions =Flow
-=item Keywords related to switch
+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>, C<continue>, C<given>, C<when>, C<default>
+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
+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.
-(These are available only if you enable the C<"switch"> feature.
-See L<feature> and L<perlsyn/"Switch statements">.)
+C<evalbytes> is only available with with the C<"evalbytes"> feature (see
+L<feature>) or if prefixed with C<CORE::>. C<__SUB__> is only available
+with 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.
=item Keywords related to scoping
-C<caller>, C<import>, C<local>, C<my>, C<our>, C<state>, C<package>,
-C<use>
+=for Pod::Functions =Namespace
-(C<state> is available only if the C<"state"> feature is enabled. See
-L<feature>.)
+C<caller>, C<import>, C<local>, C<my>, C<our>, C<package>, C<state>, C<use>
+
+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.
=item Miscellaneous functions
-C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<our>,
-C<reset>, C<scalar>, C<state>, C<undef>, C<wantarray>
+=for Pod::Functions =Misc
+
+C<defined>, C<formline>, C<lock>, C<prototype>, C<reset>, C<scalar>, C<undef>
=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<setpgrp>, C<setpriority>, C<sleep>, C<system>,
+C<pipe>, C<qx//>, C<readpipe>, C<setpgrp>,
+C<setpriority>, C<sleep>, C<system>,
C<times>, C<wait>, C<waitpid>
=item Keywords related to Perl modules
X<module>
+=for Pod::Functions =Modules
+
C<do>, C<import>, C<no>, C<package>, C<require>, C<use>
=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>
=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>
=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>
=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>
=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>,
=item Time-related functions
X<time> X<date>
-C<gmtime>, C<localtime>, C<time>, C<times>
-
-=item Functions new in perl5
-X<perl5>
+=for Pod::Functions =Time
-C<abs>, C<bless>, C<break>, C<chomp>, C<chr>, C<continue>, C<default>,
-C<exists>, C<formline>, C<given>, C<glob>, C<import>, C<lc>, C<lcfirst>,
-C<lock>, C<map>, C<my>, C<no>, C<our>, C<prototype>, C<qr//>, C<qw//>, C<qx//>,
-C<readline>, C<readpipe>, C<ref>, C<sub>*, C<sysopen>, C<tie>, C<tied>, C<uc>,
-C<ucfirst>, C<untie>, C<use>, C<when>
+C<gmtime>, C<localtime>, C<time>, C<times>
-* C<sub> was a keyword in Perl 4, but in Perl 5 it is an
-operator, which can be used in expressions.
+=item Non-function keywords
-=item Functions obsoleted in perl5
+=for Pod::Functions =!Non-functions
-C<dbmclose>, C<dbmopen>
+C<and>, C<AUTOLOAD>, C<BEGIN>, C<CHECK>, C<cmp>, C<CORE>, C<__DATA__>,
+C<default>, C<DESTROY>, C<else>, C<elseif>, C<elsif>, C<END>, C<__END__>,
+C<eq>, C<for>, C<foreach>, C<ge>, C<given>, C<gt>, C<if>, C<INIT>, C<le>,
+C<lt>, C<ne>, C<not>, C<or>, C<UNITCHECK>, C<unless>, C<until>, C<when>,
+C<while>, C<x>, C<xor>
=back
Perl was born in Unix and can therefore access all common Unix
system calls. In non-Unix environments, the functionality of some
-Unix system calls may not be available, or details of the available
+Unix system calls may not be available or details of the available
functionality may differ slightly. The Perl functions affected
by this are:
=item -X
+=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,
and tests the associated file to see if something is true about it. If the
following a minus are interpreted as file tests.
These operators are exempt from the "looks like a function rule" described
-above. That is, an opening parenthesis after the operator does not affect
-how much of the following code constitutes the argument. Put the opening
+above. That is, an opening parenthesis after the operator does not affect
+how much of the following code constitutes the argument. Put the opening
parentheses before the operator to separate it from code that follows (this
applies only to operators with higher precedence than unary operators, of
course):
access(2) family of system calls. Also note that the C<-x> and C<-X> 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
+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
As of Perl 5.9.1, as a form of purely syntactic sugar, you can stack file
test operators, in a way that C<-f -w -x $file> is equivalent to
-C<-x $file && -w _ && -f _>. (This is only fancy fancy: if you use
+C<-x $file && -w _ && -f _>. (This is only fancy fancy: if you use
the return value of C<-f $file> as an argument to another filetest
operator, no special magic will happen.)
+Portability issues: L<perlport/-X>.
+
+To avoid confusing would-be users of your code with mysterious
+syntax errors, put something like this at the top of your script:
+
+ use 5.010; # so filetest ops can stack
+
=item abs VALUE
X<abs> X<absolute>
=item abs
+=for Pod::Functions absolute value function
+
Returns the absolute value of its argument.
If VALUE is omitted, uses C<$_>.
=item accept NEWSOCKET,GENERICSOCKET
X<accept>
+=for Pod::Functions accept an incoming socket connect
+
Accepts an incoming socket connect, just as accept(2)
does. Returns the packed address if it succeeded, false otherwise.
See the example in L<perlipc/"Sockets: Client/Server Communication">.
=item alarm
+=for Pod::Functions schedule a SIGALRM
+
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<$_> is used. (On some machines,
+specified, the value stored in C<$_> 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.)
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.
+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>.
For more information see L<perlipc>.
+Portability issues: L<perlport/alarm>.
+
=item atan2 Y,X
X<atan2> X<arctangent> X<tan> X<tangent>
+=for Pod::Functions arctangent of Y/X in the range -PI to PI
+
Returns the arctangent of Y/X in the range -PI to PI.
For the tangent operation, you may use the C<Math::Trig::tan>
The return value for C<atan2(0,0)> is implementation-defined; consult
your atan2(3) manpage for more information.
+Portability issues: L<perlport/atan2>.
+
=item bind SOCKET,NAME
X<bind>
+=for Pod::Functions binds an address to a socket
+
Binds a network address to a socket, just as 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
=item binmode FILEHANDLE
+=for Pod::Functions prepare binary files for I/O
+
Arranges for FILEHANDLE to be read or written in "binary" or "text"
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).
-On some systems (in general, DOS and Windows-based systems) binmode()
+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 UTF-8 encoded Unicode, not bytes.
+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.
If LAYER is present it is a single string, but may contain multiple
-directives. The directives alter the behaviour of the filehandle.
+directives. The directives alter the behaviour of the filehandle.
When LAYER is present, using binmode on a text file makes sense.
If LAYER is omitted or specified as C<:raw> the filehandle is made
-suitable for passing binary data. This includes turning off possible CRLF
+suitable for passing binary data. This includes turning off possible CRLF
translation and marking it as bytes (as opposed to Unicode characters).
Note that, despite what may be implied in I<"Programming Perl"> (the
Camel, 3rd edition) or elsewhere, C<:raw> is I<not> simply the inverse of C<:crlf>.
Other layers that would affect the binary nature of the stream are
-I<also> disabled. See L<PerlIO>, L<perlrun>, and the discussion about the
+I<also> disabled.
See L<PerlIO>, L<perlrun>, and the discussion about the
PERLIO environment variable.
The C<:bytes>, C<:crlf>, C<:utf8>, and any other directives of the
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(utf8)>.
+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(utf8)> checks the data for actually being valid
-UTF-8. More details can be found in L<PerlIO::encoding>.
+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
internally Perl operates on UTF8-encoded Unicode characters.
The operating system, device drivers, C libraries, and Perl run-time
-system all work together to let the programmer treat a single
-character (C<\n>) as the line terminator, irrespective of the external
+system all conspire to let the programmer treat a single
+character (C<\n>) as the line terminator, irrespective of external
representation. On many operating systems, the native text file
representation matches the internal representation, but on some
platforms the external representation of C<\n> is made up of more than
one character.
-Mac OS, all variants of Unix, and Stream_LF files on VMS use a single
-character to end each line in the external representation of text (even
-though that single character is CARRIAGE RETURN on Mac OS and 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.
+All variants of Unix, Mac OS (old and new), and Stream_LF files on VMS use
+a single character to end each line in the external representation of text
+(even though that single character is CARRIAGE RETURN on old, pre-Darwin
+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.
in L<perlvar> for how to manually set your input and output
line-termination sequences.
+Portability issues: L<perlport/binmode>.
+
=item bless REF,CLASSNAME
X<bless>
=item bless REF
+=for Pod::Functions create an object
+
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<perltoot> and L<perlobj> for more about the blessing (and blessings)
-of objects.
+SeeL<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 pragmata. 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.
=item break
+=for Pod::Functions +switch 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.
+This keyword is enabled by the C<"switch"> feature: see
+L<feature> for more information. You can also access it by
+prefixing it with C<CORE::>. Alternately, include a C<use
+v5.10> or later to the current scope.
=item caller EXPR
X<caller> X<call stack> X<stack> X<stack trace>
=item caller
+=for Pod::Functions get context of the current subroutine call
+
Returns the context of the current 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
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
+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.
-Furthermore, when called from within the DB package, caller returns more
+Furthermore, when called from within the DB package in
+list context, and with an argument, caller returns more
detailed information: it sets the list variable C<@DB::args> to be the
arguments with which the subroutine was invoked.
C<< N > 1 >>. In particular, C<@DB::args> might have information from the
previous time C<caller> was called.
-Also be aware that setting C<@DB::args> is I<best effort>, intended for
-debugging or generating backtraces, and should not be relied upon. In
+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
+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
+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, and not if a
-reference to C<@_> has been taken, and subject to the caveat about reallocated
+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.
+initial state of C<@_>. Buyer beware.
=item chdir EXPR
X<chdir>
=item chdir
-Changes the working directory to EXPR, if possible. If EXPR is omitted,
+=for Pod::Functions change your current working directory
+
+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>.
+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>.
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),
=item chmod LIST
X<chmod> X<permission> X<mode>
+=for Pod::Functions changes the permissions on a list of files
+
Changes the permissions of a list of files. The first element of the
-list must be the numerical mode, which should probably be an octal
+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</oct> if all you have is a string.
$cnt = chmod 0755, "foo", "bar";
chmod 0755, @executables;
chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
# Identical to the chmod 0755 of the example above.
+Portability issues: L<perlport/chmod>.
+
=item chomp VARIABLE
X<chomp> X<INPUT_RECORD_SEPARATOR> X<$/> X<newline> X<eol>
=item chomp
+=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
$INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total
=item chop
+=for Pod::Functions remove the last character from a string
+
Chops off the last character of a string and returns the character
chopped. It is much more efficient than C<s/.$//s> because it neither
scans nor copies the string. If VARIABLE is omitted, chops C<$_>.
=item chown LIST
X<chown> X<owner> X<user> X<group>
+=for Pod::Functions change the ownership on a list of files
+
Changes the owner (and group) of a list of files. The first two
elements of the list must be the I<numeric> uid and gid, in that
order. A value of -1 in either position is interpreted by most
use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
$can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);
+Portability issues: L<perlport/chmod>.
+
=item chr NUMBER
X<chr> X<character> X<ASCII> X<Unicode>
=item chr
+=for Pod::Functions get character this number represents
+
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
chr(0x263a) is a Unicode smiley face.
=item chroot
+=for Pod::Functions make directory new root for path lookups
+
This function works like the system call by the same name: it makes the
named directory the new root directory for all further pathnames that
begin with a C</> by your process and all its children. (It doesn't
reasons, this call is restricted to the superuser. If FILENAME is
omitted, does a C<chroot> to C<$_>.
+Portability issues: L<perlport/chroot>.
+
=item close FILEHANDLE
X<close>
=item close
+=for Pod::Functions close file (or pipe or socket) handle
+
Closes the file or pipe associated with the filehandle, flushes the IO
buffers, and closes the system file descriptor. Returns true if those
-operations have succeeded and if no error was reported by any PerlIO
+operations succeed and if no error was reported by any PerlIO
layer. Closes the currently selected filehandle if the argument is
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
-C<open>.) However, an explicit C<close> on an input file resets the line
+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
or die "Can't open 'foo' for input: $!";
FILEHANDLE may be an expression whose value can be used as an indirect
-filehandle, usually the real filehandle name.
+filehandle, usually the real filehandle name or an autovivified handle.
=item closedir DIRHANDLE
X<closedir>
+=for Pod::Functions close directory handle
+
Closes a directory opened by C<opendir> 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).
Returns true if it succeeded, false otherwise. NAME should be a
packed address of the appropriate type for the socket. See the examples in
=item continue
-C<continue> is actually a flow control statement rather than a function. If
+=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
empty one, logically enough, so C<next> goes directly back
to check the condition at the top of the loop.
-If the C<"switch"> feature is enabled, C<continue> is also a
-function that exits the current C<when> (or C<default>) block and
-falls through to the next one. See L<feature> and
-L<perlsyn/"Switch statements"> for more information.
-
+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.
=item cos EXPR
X<cos> X<cosine> X<acos> X<arccosine>
=item cos
+=for Pod::Functions cosine function
+
Returns the cosine of EXPR (expressed in radians). If EXPR is omitted,
takes the cosine of C<$_>.
X<crypt> X<digest> X<hash> X<salt> X<plaintext> X<password>
X<decrypt> X<cryptography> X<passwd> X<encrypt>
+=for Pod::Functions one-way passwd-style encryption
+
Creates a digest string exactly like the crypt(3) function in the C
library (assuming that you actually have a version there that has not
been extirpated as a potential munition).
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, do not assume
-anything about the returned string itself, or how many bytes in the
-digest matter.
+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
-the first eight bytes of PLAINTEXT mattered. But alternative
+the first eight bytes of PLAINTEXT mattered. But alternative
hashing schemes (like MD5), higher level security schemes (like C2),
and implementations on non-Unix platforms may produce different
strings.
(on that copy). If that works, good. If not, crypt() dies with
C<Wide character in crypt>.
+Portability issues: L<perlport/crypt>.
+
=item dbmclose HASH
X<dbmclose>
+=for Pod::Functions breaks binding on a tied dbm file
+
[This function has been largely superseded by the C<untie> function.]
Breaks the binding between a DBM file and a hash.
+Portability issues: L<perlport/dbmclose>.
+
=item dbmopen HASH,DBNAME,MASK
X<dbmopen> X<dbm> X<ndbm> X<sdbm> X<gdbm>
-[This function has been largely superseded by the C<tie> function.]
+=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>). If your system supports
+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
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
dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
or die "Can't open netscape history file: $!";
+Portability issues: L<perlport/dbmopen>.
+
=item defined EXPR
X<defined> X<undef> X<undefined>
=item defined
+=for Pod::Functions test whether a value, variable, or function is defined
+
Returns a Boolean value telling whether EXPR has a value other than
the undefined value C<undef>. If EXPR is not present, C<$_> is
checked.
Examples:
- print if defined $switch{'D'};
+ print if defined $switch{D};
print "$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"; }
$debugging = 0 unless defined $debugging;
-Note: Many folks tend to overuse C<defined>, and then are surprised to
+Note: Many folks tend to overuse C<defined> and are then surprised to
discover that the number C<0> and C<""> (the zero-length string) are, in fact,
defined values. For example, if you say
=item delete EXPR
X<delete>
+=for Pod::Functions deletes a value from a hash
+
Given an expression that specifies an element or slice of a hash, C<delete>
deletes the specified elements from that hash so that exists() on that element
no longer returns true. Setting a hash element to the undefined value does
not remove its key, but deleting it does; see L</exists>.
-It returns the value or values deleted in list context, or the last such
+In list context, returns the value or values deleted, or the last such
element in scalar context. The return list's length always matches that of
the argument list: deleting non-existent elements returns the undefined value
in their corresponding positions.
array, the array's size shrinks to the position of the highest element that
still tests true for exists(), or to 0 if none do.
-B<Be aware> that calling delete on array values is deprecated and likely to
+B<WARNING:> Calling delete on array values is deprecated and likely to
be removed in a future version of Perl.
Deleting from C<%ENV> modifies the environment. Deleting from a hash tied to
=item die LIST
X<die> X<throw> X<exception> X<raise> X<$@> X<abort>
-C<die> raises an exception. Inside an C<eval> the error message is stuffed
+=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<$@> and the C<eval> is terminated with the undefined value.
If the exception is outside of all enclosing C<eval>s, then the uncaught
-exception prints LIST to C<STDERR> and exits with a non-zero value. If you
+exception prints LIST to C<STDERR> and exits with a non-zero value. If you
need to exit the process with a specific exit code, see L</exit>.
Equivalent examples:
exit 255; # last resort
The intent is to squeeze as much possible information about the likely cause
-into the limited space of the system exit code. However, as C<$!> is the value
+into the limited space of the system exit
+code. However, as C<$!> is the value
of C's C<errno>, which can be set by any system call, this means that the value
of the exit code used by C<die> can be non-predictable, so should not be relied
upon, other than to be non-zero.
=item do BLOCK
X<do> X<block>
+=for Pod::Functions turn a BLOCK into a TERM
+
Not really a function. Returns the value of the last command in the
sequence of commands indicated by BLOCK. When modified by the C<while> or
C<until> loop modifier, executes the BLOCK once before testing the loop
-condition. (On other statements the loop modifiers test the conditional
+condition. (On other statements the loop modifiers test the conditional
first.)
C<do BLOCK> does I<not> count as a loop, so the loop control statements
same, however, in that it does reparse the file every time you call it,
so you probably don't want to do this inside a loop.
-If C<do> cannot read the file, it returns undef and sets C<$!> to the
-error. If C<do> can read the file but cannot compile it, it
-returns undef and sets an error message in C<$@>. If the file is
-successfully compiled, C<do> returns the value of the last expression
-evaluated.
+If C<do> can read the file but cannot compile it, it returns C<undef> and sets
+an error message in C<$@>. 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.
Inclusion of library modules is better done with the
C<use> and C<require> operators, which also do automatic error checking
=item dump
+=for Pod::Functions create an immediate core dump
+
This function causes an immediate core dump. See also the B<-u>
command-line switch in L<perlrun>, which does the same thing.
Primarily this is so that you can use the B<undump> program (not
resulting confusion by Perl.
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
+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
typo.
-=item each HASH (or HASHREF)
+Portability issues: L<perlport/dump>.
+
+=item each HASH
X<each> X<hash, iterator>
-=item each ARRAY (or ARRAYREF)
+=item each ARRAY
X<array, iterator>
-When called in list context, returns a 2-element list consisting of the key
-and value for the next element of a hash, or the index and value for the
-next element of an array, so that you can iterate over it. When called in
-scalar context, returns only the key (not the value) in a hash, or the index
-in an array.
+=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
+consisting of the key and value for the next element of a hash. In Perl
+5.12 and later only, it will also return the index and value for the next
+element of an array so that you can iterate over it; older Perls consider
+this a syntax error. When called in scalar context, returns only the key
+(not the value) in a hash, or the index in an array.
Hash entries are returned in an apparently random order. The actual random
order is subject to change in future versions of Perl, but it is
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 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, 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:
+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, entries may be skipped or duplicated--so
+don't do that. Exception: In the current implementation, it is always safe
+to delete the item most recently returned by C<each()>, so the following
+code works properly:
while (($key, $value) = each %hash) {
print $key, "\n";
print "$key=$value\n";
}
-When given a reference to a hash or array, the argument will be
-dereferenced automatically.
+Starting with Perl 5.14, C<each> can take a scalar EXPR, which must hold
+reference to an unblessed hash or array. The argument will be dereferenced
+automatically. This aspect of C<each> is considered highly experimental.
+The exact behaviour may change in a future version of Perl.
while (($key,$value) = each $hashref) { ... }
-If the reference is a blessed object that overrides either C<%{}> or
-C<@{}>, the override will be used instead of dereferencing the underlying
-variable type. If both overrides are provided, C<%{}> will be the default.
-If this is not desired, you must dereference the argument yourself.
+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 5.012; # so keys/values/each work on arrays
+ use 5.014; # so keys/values/each work on scalars (experimental)
-See also C<keys>, C<values> and C<sort>.
+See also C<keys>, C<values>, and C<sort>.
=item eof FILEHANDLE
X<eof>
=item eof
-Returns 1 if the next read on FILEHANDLE will return end of file, or if
+=for Pod::Functions test a filehandle for its end
+
+Returns 1 if the next read on FILEHANDLE will return end of file I<or> if
FILEHANDLE is not open. FILEHANDLE may be an expression whose value
gives the real filehandle. (Note that this function actually
reads a character and then C<ungetc>s it, so isn't useful in an
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, C<eof()> will detect the end of only the
-last file. Examples:
+detect the end of each file, whereas C<eof()> will detect the end
+of the very last file only. Examples:
# reset line numbering on each input file
while (<>) {
print "--------------\n";
}
print;
- last if eof(); # needed if we're reading from a terminal
+ 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 if
-there was an error.
+input operators typically return C<undef> 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>
=item eval
+=for Pod::Functions catch exceptions or compile and run code
+
In the first form, the return value of EXPR is parsed and executed as if it
were a little Perl program. The value of the expression (which is itself
-determined within scalar context) is first parsed, and if there weren't any
-errors, executed in the lexical context of the current Perl program, so
-that any variable settings or subroutine and format definitions remain
-afterwards. Note that the value is parsed every time the C<eval> executes.
+determined within scalar context) is first parsed, and if there were no
+errors, executed as a block within the lexical context of the current Perl
+program. This means, that in particular, any outer lexical variables are
+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<$_> is treated as a string of
+characters, so C<use utf8> declarations have no effect, and source filters
+are forbidden. In the absence of the C<unicode_eval> feature, the string
+will sometimes be treated as characters and sometimes as bytes, depending
+on the internal encoding, and source filters activated within the C<eval>
+exhibit the erratic, but historical, behaviour of affecting some outer file
+scope that is still compiling. See also the L</evalbytes> keyword, which
+always treats its input as a byte stream and works properly with source
+filters, and the L<feature> pragma.
+
In the second form, the code within the BLOCK is parsed only once--at the
same time the code surrounding the C<eval> itself was parsed--and executed
within the context of the current Perl program. This form is typically
determined.
If there is a syntax error or runtime error, or a C<die> statement is
-executed, C<eval> returns an undefined value in scalar context
-or an empty list--or, for syntax errors, a list containing a single
-undefined value--in list context, and C<$@> is set to the error
-message. The discrepancy in the return values in list context is
-considered a bug by some, and will probably be fixed in a future
-release. If there was no error, C<$@> is guaranteed to be the empty
-string. Beware that using C<eval> neither silences Perl from printing
+executed, C<eval> returns C<undef> in scalar context
+or an empty list in list context, and C<$@> 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'>>.
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<$ENV{PERL_DL_NONLAZY}> is set. See L<perlrun>.
+C<eval> unless C<$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
in case 6.
Before Perl 5.14, the assignment to C<$@> occurred before restoration
-of localised variables, which means that for your code to run on older
+of localized variables, which means that for your code to run on older
versions, a temporary is required if you want to mask some but not all
errors:
An C<eval ''> executed within the C<DB> package doesn't see the usual
surrounding lexical scope, but rather the scope of the first non-DB piece
-of code that called it. You don't normally need to worry about this unless
+of code that called it. You don't normally need to worry about this unless
you are writing a Perl debugger.
+=item evalbytes EXPR
+X<evalbytes>
+
+=item evalbytes
+
+=for Pod::Functions +evalbytes similar to string eval, but intend to parse a bytestream
+
+This function is like L</eval> with a string argument, except it always
+parses its argument, or C<$_> 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 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.
+
=item exec LIST
X<exec> X<execute>
=item exec PROGRAM LIST
+=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
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 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:
+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:
exec ('foo') or print STDERR "couldn't exec foo: $!";
{ exec ('foo') }; print STDERR "couldn't exec foo: $!";
Note that C<exec> will not call your C<END> blocks, nor will it invoke
C<DESTROY> methods on your objects.
+Portability issues: L<perlport/exec>.
+
=item exists EXPR
X<exists> X<autovivification>
+=for Pod::Functions test whether a hash key is present
+
Given an expression that specifies an element of a hash, returns true if the
specified element in the hash has ever been initialized, even if the
corresponding value is undefined.
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. B<Be aware>
+obvious and is strongly tied to the use of L</delete> on arrays. B<Be aware>
that calling exists on array values is deprecated and likely to be removed in
a future version of Perl.
print "Defined\n" if defined $array[$index];
print "True\n" if $array[$index];
-A hash or array element can be true only if it's defined, and defined if
+A hash or array element can be true only if it's defined and defined only if
it exists, but the reverse doesn't necessarily hold true.
Given an expression that specifies the name of a subroutine,
if (exists &{$ref->{A}{B}{$key}}) { }
-Although the mostly deeply nested array or hash will not spring into
+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.
=item exit
+=for Pod::Functions terminate this program
+
Evaluates EXPR and exits immediately with that value. Example:
$ans = <STDIN>;
defined C<END> routines first, but these C<END> routines may not
themselves abort the exit. Likewise any object destructors that need to
be called are called before the real exit. C<END> routines and destructors
-can change the exit status by modifying C<$?>. If this is a problem, you
-can call C<POSIX:_exit($status)> to avoid END and destructor processing.
+can change the exit status by modifying C<$?>. If this is a problem, you
+can call C<POSIX::_exit($status)> to avoid END and destructor processing.
See L<perlmod> for details.
+Portability issues: L<perlport/exit>.
+
=item exp EXPR
X<exp> X<exponential> X<antilog> X<antilogarithm> X<e>
=item exp
+=for Pod::Functions raise I<e> to a power
+
Returns I<e> (the natural logarithm base) to the power of EXPR.
If EXPR is omitted, gives C<exp($_)>.
+=item fc EXPR
+X<fc> X<foldcase> X<casefold> X<fold-case> X<case-fold>
+
+=item fc
+
+=for Pod::Functions +fc return casefolded version of a string
+
+Returns the casefolded version of EXPR. This is the internal function
+implementing the C<\F> escape in double-quoted strings.
+
+Casefolding is the process of mapping strings to a form where case
+differences are erased; comparing two strings in their casefolded
+form is effectively a way of asking if two strings are equal,
+regardless of case.
+
+Roughly, if you ever found yourself writing this
+
+ lc($this) eq lc($that) # Wrong!
+ # or
+ uc($this) eq uc($that) # Also wrong!
+ # or
+ $this =~ /\Q$that/i # Right!
+
+Now you can write
+
+ fc($this) eq fc($that)
+
+And get the correct results.
+
+Perl only implements the full form of casefolding.
+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<$_>.
+
+This function behaves the same way under various pragma, such as in a locale,
+as L</lc> does.
+
+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.
+
+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.
+
=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
use Fcntl;
$flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
or die "Can't set flags for the socket: $!\n";
+Portability issues: L<perlport/fcntl>.
+
+=item __FILE__
+X<__FILE__>
+
+=for Pod::Functions the name of the current source file
+
+A special token that returns the name of the file in which it occurs.
+
=item fileno FILEHANDLE
X<fileno>
+=for Pod::Functions return file descriptor from filehandle
+
Returns the file descriptor for a filehandle, or undefined if the
-filehandle is not open. This is mainly useful for constructing
+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.
+
+This is mainly useful for constructing
bitmaps for C<select> and low-level POSIX tty-handling operations.
If FILEHANDLE is an expression, the value is taken as an indirect
filehandle, generally its name.
print "THIS and THAT are dups\n";
}
-(Filehandles connected to memory objects via new features of C<open> may
-return undefined even though they are open.)
-
-
=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
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).
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>,
-your port's specific documentation, or your system-specific local manpages
+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
free to write for your own system's idiosyncrasies (sometimes called
OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with
LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but
-you can use the symbolic names if you import them from the Fcntl module,
-either individually, or as a group using the ':flock' tag. LOCK_SH
+you can use the symbolic names if you import them from the L<Fcntl> module,
+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
+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.
To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE
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
the switch C<-Ud_flock> to the F<Configure> program when you configure
-Perl.
+and build a new Perl.
Here's a mailbox appender for BSD systems.
See also L<DB_File> for other flock() examples.
+Portability issues: L<perlport/flock>.
+
=item fork
X<fork> X<child> X<parent>
+=for Pod::Functions create a new process just like this one
+
Does a 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
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.
+
+Portability issues: L<perlport/fork>.
+
=item format
X<format>
+=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:
=item formline PICTURE,LIST
X<formline>
+=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
character may be taken to mean the beginning of an array name.
C<formline> 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 $fh, ">", \$output >>) and write to that instead.
+
=item getc FILEHANDLE
X<getc> X<getchar> X<character> X<file, read>
=item getc
+=for Pod::Functions get the next character from the filehandle
+
Returns the next character from the input file attached to FILEHANDLE,
or the undefined value at end of file or if there was an error (in
the latter case C<$!> is set). If FILEHANDLE is omitted, reads from
The C<POSIX::getattr> function can do this more portably on
systems purporting POSIX compliance. See also the C<Term::ReadKey>
-module from your nearest CPAN site; details on CPAN can be found on
+module from your nearest CPAN site; details on CPAN can be found under
L<perlmodlib/CPAN>.
=item getlogin
X<getlogin> X<login>
+=for Pod::Functions return who logged in at this tty
+
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>.
Do not consider C<getlogin> for authentication: it is not as
secure as C<getpwuid>.
+Portability issues: L<perlport/getlogin>.
+
=item getpeername SOCKET
X<getpeername> X<peer>
-Returns the packed sockaddr address of other end of the SOCKET connection.
+=for Pod::Functions find the other end of a socket connection
+
+Returns the packed sockaddr address of the other end of the SOCKET
+connection.
use Socket;
$hersockaddr = getpeername(SOCK);
=item getpgrp PID
X<getpgrp> X<group>
+=for Pod::Functions get process 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 process
-group of current process. Note that the POSIX version of C<getpgrp>
+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.
+Portability issues: L<perlport/getpgrp>.
+
=item getppid
X<getppid> X<parent> X<pid>
+=for Pod::Functions get parent process ID
+
Returns the process id of the parent process.
-Note for Linux users: on Linux, the C functions C<getpid()> and
-C<getppid()> return different values from different threads. In order to
-be portable, this behavior is not reflected by the Perl-level function
-C<getppid()>, that returns a consistent value across threads. If you want
-to call the underlying C<getppid()>, you may use the CPAN module
-C<Linux::Pid>.
+Note for Linux users: Between v5.8.1 and v5.16.0 Perl would work
+around non-POSIX thread semantics the minority of Linux systems (and
+Debian GNU/kFreeBSD systems) that used LinuxThreads, this emulation
+has since been removed. See the documentation for L<$$|perlvar/$$> for
+details.
+
+Portability issues: L<perlport/getppid>.
=item getpriority WHICH,WHO
X<getpriority> X<priority> X<nice>
+=for Pod::Functions get current nice value
+
Returns the current priority for a process, a process group, or a user.
-(See C<getpriority(2)>.) Will raise a fatal exception if used on a
+(See L<getpriority(2)>.) Will raise a fatal exception if used on a
machine that doesn't implement getpriority(2).
+Portability issues: L<perlport/getpriority>.
+
=item getpwnam NAME
X<getpwnam> X<getgrnam> X<gethostbyname> X<getnetbyname> X<getprotobyname>
X<getpwuid> X<getgrgid> X<getservbyname> X<gethostbyaddr> X<getnetbyaddr>
X<setnetent> X<setprotoent> X<setservent> X<endpwent> X<endgrent> X<endhostent>
X<endnetent> X<endprotoent> X<endservent>
+=for Pod::Functions get passwd record given user login name
+
=item getgrnam NAME
+=for Pod::Functions get group record given group name
+
=item gethostbyname NAME
+=for Pod::Functions get host record given name
+
=item getnetbyname NAME
+=for Pod::Functions get networks record given name
+
=item getprotobyname NAME
+=for Pod::Functions get protocol record given name
+
=item getpwuid UID
+=for Pod::Functions get passwd record given user ID
+
=item getgrgid GID
+=for Pod::Functions get group record given group user ID
+
=item getservbyname NAME,PROTO
+=for Pod::Functions get services record given its name
+
=item gethostbyaddr ADDR,ADDRTYPE
+=for Pod::Functions get host record given its address
+
=item getnetbyaddr ADDR,ADDRTYPE
+=for Pod::Functions get network record given its address
+
=item getprotobynumber NUMBER
+=for Pod::Functions get protocol record numeric protocol
+
=item getservbyport PORT,PROTO
+=for Pod::Functions get services record given numeric port
+
=item getpwent
+=for Pod::Functions get next passwd record
+
=item getgrent
+=for Pod::Functions get next group record
+
=item gethostent
+=for Pod::Functions get next hosts record
+
=item getnetent
+=for Pod::Functions get next networks record
+
=item getprotoent
+=for Pod::Functions get next protocols record
+
=item getservent
+=for Pod::Functions get next services record
+
=item setpwent
+=for Pod::Functions prepare passwd file for use
+
=item setgrent
+=for Pod::Functions prepare group file for use
+
=item sethostent STAYOPEN
+=for Pod::Functions prepare hosts file for use
+
=item setnetent STAYOPEN
+=for Pod::Functions prepare networks file for use
+
=item setprotoent STAYOPEN
+=for Pod::Functions prepare protocols file for use
+
=item setservent STAYOPEN
+=for Pod::Functions prepare services file for use
+
=item endpwent
+=for Pod::Functions be done using passwd file
+
=item endgrent
+=for Pod::Functions be done using group file
+
=item endhostent
+=for Pod::Functions be done using hosts file
+
=item endnetent
+=for Pod::Functions be done using networks file
+
=item endprotoent
+=for Pod::Functions be done using protocols file
+
=item endservent
+=for Pod::Functions be done using services file
+
These routines are the same as their counterparts in the
system C library. In list context, the return values from the
various get routines are as follows:
system users are able to change this information and therefore it
cannot be trusted and therefore the $gcos is tainted (see
L<perlsec>). The $passwd and $shell, user's encrypted password and
-login shell, are also tainted, because of the same reason.
+login shell, are also tainted, for the same reason.
In scalar context, you get the name, unless the function was a
lookup by name, in which case you get the other thing, whatever it is.
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 your getpwnam(3) documentation and your
+in your system, please consult 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>,
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
-and Linux.) Those systems that implement a proprietary shadow password
+and Linux). Those systems that implement a proprietary shadow password
facility are unlikely to be supported.
-The $members value returned by I<getgr*()> is a space separated list of
+The $members value returned by I<getgr*()> is a space-separated list of
the login names of the members of the group.
For the I<gethost*()> functions, if the C<h_errno> variable is supported in
$ip_address = inet_ntoa($packed_ip);
}
-Make sure <gethostbyname()> is called in SCALAR context and that
+Make sure C<gethostbyname()> 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:
+
+ 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>,
use User::pwent;
$is_his = (stat($filename)->uid == pwent($whoever)->uid);
-Even though it looks like they're the same method calls (uid),
+Even though it looks as though they're the same method calls (uid),
they aren't, because a C<File::stat> object is different from
a C<User::pwent> object.
+Portability issues: L<perlport/getpwnam> to L<perlport/endservent>.
+
=item getsockname SOCKET
X<getsockname>
+=for Pod::Functions retrieve the sockaddr for a given socket
+
Returns the packed sockaddr address of this end of the SOCKET connection,
in case you don't know the address because you have several different
IPs that the connection might have come in on.
=item getsockopt SOCKET,LEVEL,OPTNAME
X<getsockopt>
+=for Pod::Functions get socket options on a given socket
+
Queries the option named OPTNAME associated with SOCKET at a given LEVEL.
Options may exist at multiple protocol levels depending on the socket
type, but at least the uppermost socket level SOL_SOCKET (defined in the
-C<Socket> module) will exist. To query options at another level the
+C<Socket> module) will exist. To query options at another level the
protocol number of the appropriate protocol controlling the option
-should be supplied. For example, to indicate that an option is to be
+should be supplied. For example, to indicate that an option is to be
interpreted by the TCP protocol, LEVEL should be set to the protocol
number of TCP, which you can get using C<getprotobyname>.
The function returns a packed string representing the requested socket
option, or C<undef> on error, with the reason for the error placed in
-C<$!>). Just what is in the packed string depends on LEVEL and OPTNAME;
+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.
-An example to test whether Nagle's algorithm is turned on on a socket:
+Here's an example to test whether Nagle's algorithm is enabled on a socket:
use Socket qw(:all);
my $nodelay = unpack("I", $packed);
print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";
+Portability issues: L<perlport/getsockopt>.
=item glob EXPR
X<glob> X<wildcard> X<filename, expansion> X<expand>
=item glob
+=for Pod::Functions expand filenames using wildcards
+
In list context, returns a (possibly empty) list of filename expansions on
-the value of EXPR such as the standard Unix shell F</bin/csh> would do. In
+the value of EXPR such as the standard Unix shell F</bin/csh> would do. In
scalar context, glob iterates through such filename expansions, returning
-undef when the list is exhausted. This is the internal function
-implementing the C<< <*.c> >> operator, but you can use it directly. If
+undef when the list is exhausted. This is the internal function
+implementing the C<< <*.c> >> operator, but you can use it directly. If
EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in
more detail in L<perlop/"I/O Operators">.
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:
+
+ @spacies = <"*e f*">;
+ @spacies = glob '"*e f*"';
+ @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*");
If non-empty braces are the only wildcard characters used in the
C<glob>, no filenames are matched, but potentially many strings
C<File::Glob> extension. See L<File::Glob> for details, including
C<bsd_glob> which does not treat whitespace as a pattern separator.
+Portability issues: L<perlport/glob>.
+
=item gmtime EXPR
X<gmtime> X<UTC> X<Greenwich>
=item gmtime
-Works just like L<localtime> but the returned values are
+=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.
-Note: when called in list context, $isdst, the last value
-returned by gmtime is always C<0>. There is no
+Note: When called in list context, $isdst, the last value
+returned by gmtime, is always C<0>. There is no
Daylight Saving Time in GMT.
-See L<perlport/gmtime> for portability concerns.
+Portability issues: L<perlport/gmtime>.
=item goto LABEL
X<goto> X<jump> X<jmp>
=item goto &NAME
+=for Pod::Functions create spaghetti code
+
The C<goto-LABEL> form finds the statement labeled with LABEL and
-resumes execution there. It can't be used to get out of a block or
+resumes execution there. It can't be used to get out of a block or
subroutine given to C<sort>. It can be used to go almost anywhere
else within the dynamic scope, including out of subroutines, but it's
usually better to use some other construct such as C<last> or C<die>.
goto ("FOO", "BAR", "GLARCH")[$i];
+As shown in this example, C<goto-EXPR> is exempt from the "looks like a
+function" rule. A pair of parentheses following it does not (necessarily)
+delimit its argument. C<goto("NE")."XT"> is equivalent to C<goto NEXT>.
+
Use of C<goto-LABEL> or C<goto-EXPR> to jump into a construct is
deprecated and will issue a warning. Even then, it may not be used to
go into any construct that requires initialization, such as a
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
+containing a code reference or a block that evaluates to a code
reference.
=item grep BLOCK LIST
=item grep EXPR,LIST
+=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
relatives. In particular, it is not limited to using regular expressions.
=item hex
+=for Pod::Functions convert a string to a hexadecimal 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<$_>.
Hex strings may only represent integers. Strings that would cause
integer overflow trigger a warning. Leading whitespace is not stripped,
-unlike oct(). To present something as hex, look into L</printf>,
-L</sprintf>, or L</unpack>.
+unlike oct(). To present something as hex, look into L</printf>,
+L</sprintf>, and L</unpack>.
=item import LIST
X<import>
+=for Pod::Functions patch a module's namespace into your own
+
There is no builtin C<import> function. It is just an ordinary
method (subroutine) defined (or inherited) by modules that wish to export
names to another module. The C<use> function calls the C<import> method
=item index STR,SUBSTR
+=for Pod::Functions find a substring within a string
+
The index function searches for one string within another, but without
the wildcard-like behavior of a full regular-expression pattern match.
It returns the position of the first occurrence of SUBSTR in STR at
or after POSITION. If POSITION is omitted, starts searching from the
beginning of the string. POSITION before the beginning of the string
or after its end is treated as if it were the beginning or the end,
-respectively. POSITION and the return value are based at C<0> (or whatever
-you've set the C<$[> variable to--but don't do that). If the substring
-is not found, C<index> returns one less than the base, ordinarily C<-1>.
+respectively. POSITION and the return value are based at zero.
+If the substring is not found, C<index> returns -1.
=item int EXPR
X<int> X<integer> X<truncate> X<trunc> X<floor>
=item int
+=for Pod::Functions get the integer portion of a number
+
Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>.
You should not use this function for rounding: one because it truncates
towards C<0>, and two because machine representations of floating-point
=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
require "sys/ioctl.ph"; # probably in $Config{archlib}/sys/ioctl.ph
The special string C<"0 but true"> is exempt from B<-w> complaints
about improper numeric conversions.
+Portability issues: L<perlport/ioctl>.
+
=item join EXPR,LIST
X<join>
+=for Pod::Functions join a list into a string using a separator
+
Joins the separate strings of LIST into a single string with fields
separated by the value of EXPR, and returns that new string. Example:
Beware that unlike C<split>, C<join> doesn't take a pattern as its
first argument. Compare L</split>.
-=item keys HASH (or HASHREF)
+=item keys HASH
X<keys> X<key>
-=item keys ARRAY (or ARRAYREF)
+=item keys ARRAY
-Returns a list consisting of all the keys of the named hash, or the indices
-of an array. (In scalar context, returns the number of keys or indices.)
+=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
+named hash, or in Perl 5.12 or later only, the indices of an array. Perl
+releases prior to 5.12 will produce a syntax error if you try to use an
+array argument. In scalar context, returns the number of keys or indices.
The keys of a hash are returned in an apparently random order. The actual
random order is subject to change in future versions of Perl, but it
Perl for security reasons (see L<perlsec/"Algorithmic Complexity
Attacks">).
-As a side effect, calling keys() resets the HASH or ARRAY's internal iterator
+As a side effect, calling keys() resets the internal interator of the HASH or ARRAY
(see L</each>). In particular, calling keys() in void context resets
the iterator with no other overhead.
%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
+as trying has no effect). C<keys @array> in an lvalue context is a syntax
error.
-When given a reference to a hash or array, the argument will be
-dereferenced automatically.
+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.
for (keys $hashref) { ... }
for (keys $obj->get_arrayref) { ... }
-If the reference is a blessed object that overrides either C<%{}> or
-C<@{}>, the override will be used instead of dereferencing the underlying
-variable type. If both overrides are provided, C<%{}> will be the default.
-If this is not desired, you must dereference the argument yourself.
+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:
-See also C<each>, C<values> and C<sort>.
+ 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>.
=item kill SIGNAL, LIST
+
+=item kill SIGNAL
X<kill> X<signal>
+=for Pod::Functions send a signal to a process or process group
+
Sends a signal to a list of processes. Returns the number of
processes successfully signaled (which is not necessarily the
same as the number actually killed).
L<perlport> for notes on the portability of this construct.
Unlike in the shell, if SIGNAL is negative, it kills process groups instead
-of processes. That means you usually want to use positive not negative signals.
+of processes. That means you usually
+want to use positive not negative signals.
You may also use a signal name in quotes.
The behavior of kill when a I<PROCESS> number is zero or negative depends on
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.
+This emulation has limitations related to kill that have to be considered,
+for code running on Windows and in code intended to be portable.
+
+See L<perlfork> for more details.
+
+If there is no I<LIST> of processes, no signal is sent, and the return
+value is 0. This form is sometimes used, however, because it causes
+tainting checks to be run. But see
+L<perlsec/Laundering and Detecting Tainted Data>.
+
+Portability issues: L<perlport/kill>.
+
=item last LABEL
X<last> X<break>
=item last
+=for Pod::Functions exit a block prematurely
+
The C<last> 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> 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
+C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit
a grep() or map() operation.
Note that a block by itself is semantically identical to a loop
=item lc
+=for Pod::Functions return lower-case version of a string
+
Returns a lowercased version of EXPR. This is the internal function
implementing the C<\L> escape in double-quoted strings.
=back
-=item Otherwise, If EXPR has the UTF8 flag set
+=item Otherwise, if C<use locale> (but not C<use locale ':not_characters'>) is in effect:
+
+Respects current LC_CTYPE locale for code points < 256; and uses Unicode
+semantics for the remaining code points (this last can only happen if
+the UTF8 flag is also set). See L<perllocale>.
-If the current package has a subroutine named C<ToLower>, it will be used to
-change the case
-(See L<perlunicode/"User-Defined Case Mappings (for serious hackers only)">.)
-Otherwise Unicode semantics are used for the case change.
+A deficiency in this is that case changes that cross the 255/256
+boundary are not well-defined. For example, the lower case of LATIN CAPITAL
+LETTER SHARP S (U+1E9E) in Unicode semantics is U+00DF (on ASCII
+platforms). But under C<use locale>, the lower case of U+1E9E is
+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
+the input character unchanged, for all instances (and there aren't
+many) where the 255/256 boundary would otherwise be crossed.
-=item Otherwise, if C<use locale> is in effect
+=item Otherwise, If EXPR has the UTF8 flag set:
-Respects current LC_CTYPE locale. See L<perllocale>.
+Unicode semantics are used for the case change.
-=item Otherwise, if C<use feature 'unicode_strings'> is in effect:
+=item Otherwise, if C<use feature 'unicode_strings'> or C<use locale ':not_characters'>) is in effect:
-Unicode semantics are used for the case change. Any subroutine named
-C<ToLower> will not be used.
+Unicode semantics are used for the case change.
=item Otherwise:
=item lcfirst
+=for Pod::Functions return a string with just the next letter in lower case
+
Returns the value of EXPR with the first character lowercased. This
is the internal function implementing the C<\l> escape in
double-quoted strings.
If EXPR is omitted, uses C<$_>.
-This function behaves the same way under various pragma, such as in a locale,
+This function behaves the same way under various pragmata, such as in a locale,
as L</lc> does.
=item length EXPR
=item length
+=for Pod::Functions return the number of bytes in a string
+
Returns the length in I<characters> of the value of EXPR. If EXPR is
-omitted, returns length of C<$_>. If EXPR is undefined, returns C<undef>.
+omitted, returns the length of C<$_>. If EXPR is undefined, returns
+C<undef>.
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
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>.
+=item __LINE__
+X<__LINE__>
+
+=for Pod::Functions the current source line number
+
+A special token that compiles to the current line number.
+
=item link OLDFILE,NEWFILE
X<link>
+=for Pod::Functions create a hard link in the filesystem
+
Creates a new filename linked to the old filename. Returns true for
success, false otherwise.
+Portability issues: L<perlport/link>.
+
=item listen SOCKET,QUEUESIZE
X<listen>
+=for Pod::Functions register your socket as a server
+
Does the same thing that the listen(2) system call does. Returns true if
it succeeded, false otherwise. See the example in
L<perlipc/"Sockets: Client/Server Communication">.
=item local EXPR
X<local>
+=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.
=item localtime
+=for Pod::Functions convert UNIX time into record or string using local time
+
Converts a time as returned by the time function to a 9-element list
with the time analyzed for the local time zone. Typically used as
follows:
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
localtime(time);
-All list elements are numeric, and come straight out of the C `struct
+All list elements are numeric and come straight out of the C `struct
tm'. C<$sec>, C<$min>, and C<$hour> are the seconds, minutes, and hours
of the specified time.
-C<$mday> is the day of the month, and C<$mon> is the month itself, in
-the range C<0..11> with 0 indicating January and 11 indicating December.
+C<$mday> is the day of the month and C<$mon> the month in
+the range C<0..11>, with 0 indicating January and 11 indicating December.
This makes it easy to get a month name from a list:
my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
print "$abbr[$mon] $mday";
# $mon=9, $mday=18 gives "Oct 18"
-C<$year> is the number of years since 1900, not just the last two digits
-of the year. That is, C<$year> is C<123> in year 2023. The proper way
-to get a 4-digit year is simply:
+C<$year> contains the number of years since 1900. To get a 4-digit
+year write:
$year += 1900;
-Otherwise you create non-Y2K-compliant programs--and you wouldn't want
-to do that, would you?
-
-To get the last two digits of the year (e.g., '01' in 2001) do:
+To get the last two digits of the year (e.g., "01" in 2001) do:
$year = sprintf("%02d", $year % 100);
$now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994"
-This scalar value is B<not> locale dependent but is a Perl builtin. For GMT
-instead of local time use the L</gmtime> builtin. See also the
-C<Time::Local> module (to convert the second, minutes, hours, ... back to
+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.
-To get somewhat similar but locale dependent date strings, set up your
+To get somewhat similar but locale-dependent date strings, set up your
locale environment variables appropriately (please see L<perllocale>) and
try for example:
Note that the 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.
-See L<perlport/localtime> for portability concerns.
-
-The L<Time::gmtime> and L<Time::localtime> modules provides a convenient,
+The L<Time::gmtime> and L<Time::localtime> modules provide a convenient,
by-name access mechanism to the gmtime() and localtime() functions,
respectively.
For a comprehensive date and time representation look at the
L<DateTime> module on CPAN.
+Portability issues: L<perlport/localtime>.
+
=item lock THING
X<lock>
-This function places an advisory lock on a shared variable, or referenced
+=for Pod::Functions +5.005 get a thread lock on a variable, subroutine, or method
+
+This function places an advisory lock on a shared variable or referenced
object contained in I<THING> until the lock goes out of scope.
+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
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.
=item log
+=for Pod::Functions retrieve the natural logarithm for a number
+
Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted,
-returns log of C<$_>. To get the log of another base, use basic algebra:
+returns the log of C<$_>. To get the
+log of another base, use basic algebra:
The base-N log of a number is equal to the natural log of that number
divided by the natural log of N. For example:
See also L</exp> for the inverse operation.
-=item lstat EXPR
+=item lstat FILEHANDLE
X<lstat>
+=item lstat EXPR
+
+=item lstat DIRHANDLE
+
=item lstat
+=for Pod::Functions stat a symbolic link
+
Does the same thing as the C<stat> function (including setting the
special C<_> filehandle) but stats a symbolic link instead of the file
the symbolic link points to. If symbolic links are unimplemented on
If EXPR is omitted, stats C<$_>.
+Portability issues: L<perlport/lstat>.
+
=item m//
+=for Pod::Functions match a string with a regular expression pattern
+
The match operator. See L<perlop/"Regexp Quote-Like Operators">.
=item map BLOCK LIST
=item map EXPR,LIST
+=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
results of each such evaluation. In scalar context, returns the
my @squares = map { $_ > 5 ? ($_ * $_) : () } @numbers;
shows that number of returned elements can differ from the number of
-input elements. To omit an element, return an empty list ().
+input elements. To omit an element, return an empty list ().
This could also be achieved by writing
my @squares = map { $_ * $_ } grep { $_ > 5 } @numbers;
which makes the intention more clear.
-Map always returns a list which can be assigned to a hash where the elements
-become key/value pairs. See L<perldata> for more details.
+Map always returns a list, which can be
+assigned to a hash such that the elements
+become key/value pairs. See L<perldata> for more details.
%hash = map { get_a_key_for($_) => $_ } @array;
can't be seen from the outside, avoiding any potential side-effects.
C<{> starts both hash references and blocks, so C<map { ...> could be either
-the start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look
+the start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look
ahead for the closing C<}> it has to take a guess at which it's dealing with
-based on what it finds just after the C<{>. Usually it gets it right, but if it
+based on what it finds just after the
+C<{>. Usually it gets it right, but if it
doesn't it won't realize something is wrong until it gets to the C<}> and
-encounters the missing (or unexpected) comma. The syntax error will be
+encounters the missing (or unexpected) comma. The syntax error will be
reported close to the C<}>, but you'll need to change something near the C<{>
such as using a unary C<+> to give Perl some help:
=item mkdir
+=for Pod::Functions create a directory
+
Creates the directory specified by FILENAME, with permissions
specified by MASK (as modified by C<umask>). If it succeeds it
-returns true, otherwise it returns false and sets C<$!> (errno).
-If omitted, MASK defaults to 0777. If omitted, FILENAME defaults
-to C<$_>.
+returns true; otherwise it returns false and sets C<$!> (errno).
+MASK defaults to 0777 if omitted, and FILENAME defaults
+to C<$_> if omitted.
-In general, it is better to create directories with permissive MASK,
-and let the user modify that with their C<umask>, than it is to supply
+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
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
=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
use IPC::SysV;
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">, C<IPC::SysV>, and C<IPC::Semaphore> documentation.
+L<perlipc/"SysV IPC"> and the documentation for C<IPC::SysV> and
+C<IPC::Semaphore>.
+
+Portability issues: L<perlport/msgctl>.
=item msgget KEY,FLAGS
X<msgget>
+=for Pod::Functions get SysV IPC message queue
+
Calls the System V IPC function msgget(2). Returns the message queue
-id, or the undefined value if there is an error. See also
-L<perlipc/"SysV IPC"> and C<IPC::SysV> and C<IPC::Msg> documentation.
+id, or C<undef> on error. See also
+L<perlipc/"SysV IPC"> and the documentation for C<IPC::SysV> and
+C<IPC::Msg>.
+
+Portability issues: L<perlport/msgget>.
=item msgrcv ID,VAR,SIZE,TYPE,FLAGS
X<msgrcv>
+=for Pod::Functions receive a SysV IPC message from a message queue
+
Calls the System V IPC function msgrcv to receive a message from
message queue ID into variable VAR with a maximum message size of
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, or false if there is
-an error. See also L<perlipc/"SysV IPC">, C<IPC::SysV>, and
-C<IPC::SysV::Msg> documentation.
+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>.
+
+Portability issues: L<perlport/msgrcv>.
=item msgsnd ID,MSG,FLAGS
X<msgsnd>
+=for Pod::Functions send a SysV IPC message to a message queue
+
Calls the System V IPC function msgsnd to send the message MSG to the
message queue ID. MSG must begin with the native long integer message
-type, and be followed by the length of the actual message, and finally
+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,
-or false if there is an error. See also C<IPC::SysV>
+false on error. See also the C<IPC::SysV>
and C<IPC::SysV::Msg> documentation.
+Portability issues: L<perlport/msgsnd>.
+
=item my EXPR
X<my>
=item my TYPE EXPR : ATTRS
+=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 value is listed,
the list must be placed in parentheses.
The exact semantics and interface of TYPE and ATTRS are still
-evolving. TYPE is currently bound to the use of C<fields> pragma,
+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>,
=item next
+=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:
refers to the innermost enclosing loop.
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
+C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit
a grep() or map() operation.
Note that a block by itself is semantically identical to a loop
=item no VERSION
+=for Pod::Functions unimport some module symbols or semantics at compile time
+
See the C<use> function, of which C<no> is the opposite.
=item oct EXPR
=item oct
+=for Pod::Functions convert a string to an octal number
+
Interprets EXPR as an octal string and returns the corresponding
value. (If EXPR happens to start off with C<0x>, interprets it as a
hex string. If EXPR starts off with C<0b>, it is interpreted as a
=item open FILEHANDLE
+=for Pod::Functions open a file, pipe, or descriptor
+
Opens the file whose filename is given by EXPR, and associates it with
FILEHANDLE.
Simple examples to open a file for reading:
- open(my $fh, '<', "input.txt") or die $!;
+ open(my $fh, "<", "input.txt")
+ or die "cannot open < input.txt: $!";
and for writing:
- open(my $fh, '>', "output.txt") or die $!;
+ open(my $fh, ">", "output.txt")
+ or die "cannot open > output.txt: $!";
(The following is a comprehensive reference to open(): for a gentler
introduction you may consider L<perlopentut>.)
-If FILEHANDLE is an undefined scalar variable (or array or hash element)
-the variable is assigned a reference to a new anonymous filehandle,
-otherwise if FILEHANDLE is an expression, its value is used as the name of
-the real filehandle wanted. (This is considered a symbolic reference, so
-C<use strict 'refs'> should I<not> be in effect.)
-
-If EXPR is omitted, the scalar variable of the same name as the
-FILEHANDLE contains the filename. (Note that lexical variables--those
-declared with C<my>--will not work for this purpose; so if you're
-using C<my>, specify EXPR in your call to open.)
-
-If three or more arguments are specified then the mode of opening and
-the filename are separate. If MODE is C<< '<' >> or nothing, the file
-is opened for input. If MODE is C<< '>' >>, the file is truncated and
-opened for output, being created if necessary. If MODE is C<<< '>>' >>>,
-the file is opened for appending, again being created if necessary.
-
-You can put a C<'+'> in front of the C<< '>' >> or C<< '<' >> to
+If FILEHANDLE is an undefined scalar variable (or array or hash element), a
+new filehandle is autovivified, meaning that the variable is assigned a
+reference to a newly allocated anonymous filehandle. Otherwise if
+FILEHANDLE is an expression, its value is the real filehandle. (This is
+considered a symbolic reference, so C<use strict "refs"> should I<not> be
+in effect.)
+
+If EXPR is omitted, the global (package) scalar variable of the same
+name as the FILEHANDLE contains the filename. (Note that lexical
+variables--those declared with C<my> or C<state>--will not work for this
+purpose; so if you're using C<my> or C<state>, specify EXPR in your
+call to open.)
+
+If three (or more) arguments are specified, the open mode (including
+optional encoding) in the second argument are distinct from the filename in
+the third. If MODE is C<< < >> or nothing, the file is opened for input.
+If MODE is C<< > >>, the file is opened for output, with existing files
+first being truncated ("clobbered") and nonexisting files newly created.
+If MODE is C<<< >> >>>, the file is opened for appending, again being
+created if necessary.
+
+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<< '+>' >> mode would clobber the file first. You can't usually use
+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
+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.
-These various prefixes correspond to the fopen(3) modes of C<'r'>,
-C<'r+'>, C<'w'>, C<'w+'>, C<'a'>, and C<'a+'>.
+These various prefixes correspond to the fopen(3) modes of C<r>,
+C<r+>, C<w>, C<w+>, C<a>, and C<a+>.
-In the two-argument (and one-argument) form of the call, the mode and
-filename should be concatenated (in that order), possibly separated by
-spaces. You may omit the mode in these forms when that mode is
-C<< '<' >>.
+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.
-If the filename begins with C<'|'>, the filename is interpreted as a
-command to which output is to be piped, and if the filename ends with a
-C<'|'>, the filename is interpreted as a command that pipes output to
-us. 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 L<perlipc/"Bidirectional Communication with Another Process">
-for alternatives.)
-
-For three or more arguments if MODE is C<'|-'>, the filename is
+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
-is C<'-|'>, the filename is interpreted as a command that pipes
+is C<-|>, the filename is interpreted as a command that pipes
output to us. In the two-argument (and one-argument) form, one should
-replace dash (C<'-'>) with the command.
+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
defined, but experimental "layers" may give extra LIST arguments
meaning.
-In the two-argument (and one-argument) form, opening C<< '<-' >>
-or C<'-'> opens STDIN and opening C<< '>-' >> opens STDOUT.
+In the two-argument (and one-argument) form, opening C<< <- >>
+or C<-> opens STDIN and opening C<< >- >> opens STDOUT.
-You may use the three-argument form of open to specify I/O layers
-(sometimes referred to as "disciplines") to apply to the handle
+You may (and usually should) use the three-argument form of open to specify
+I/O layers (sometimes referred to as "disciplines") to apply to the handle
that affect how the input and output are processed (see L<open> and
-L<PerlIO> for more details). For example:
+L<PerlIO> for more details). For example:
open(my $fh, "<:encoding(UTF-8)", "filename")
|| die "can't open UTF-8 encoded filename: $!";
-opens the UTF-8 encoded file containing Unicode characters;
-see L<perluniintro>. Note that if layers are specified in the
+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.
+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
modules that can help with that problem)) always check
the return value from opening a file.
-As a special case the 3-arg form with a read/write mode and the third
+As a special case the three-argument form with a read/write mode and the third
argument being C<undef>:
open(my $tmp, "+>", undef) or die ...
-opens a filehandle to an anonymous temporary file. Also using "+<"
+opens a filehandle to an anonymous temporary file. Also using C<< +< >>
works for symmetry, but you really should consider writing something
to the temporary file first. You will need to seek() to do the
reading.
Since v5.8.0, Perl has built using PerlIO by default. Unless you've
-changed this (i.e., Configure -Uuseperlio), you can open filehandles
-directly to Perl scalars via:
+changed this (such as building Perl with C<Configure -Uuseperlio>), you can
+open filehandles directly to Perl scalars via:
- open($fh, '>', \$variable) || ..
+ open($fh, ">", \$variable) || ..
To (re)open C<STDOUT> or C<STDERR> as an in-memory file, close it first:
close STDOUT;
- open STDOUT, '>', \$variable or die "Can't open STDOUT: $!";
+ open(STDOUT, ">", \$variable)
+ or die "Can't open STDOUT: $!";
General examples:
$ARTICLE = 100;
- open ARTICLE or die "Can't find article $ARTICLE: $!\n";
+ open(ARTICLE) or die "Can't find article $ARTICLE: $!\n";
while (<ARTICLE>) {...
- open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved)
+ open(LOG, ">>/usr/spool/news/twitlog"); # (log is reserved)
# if the open fails, output is discarded
- open(my $dbase, '+<', 'dbase.mine') # open for update
+ open(my $dbase, "+<", "dbase.mine") # open for update
or die "Can't open 'dbase.mine' for update: $!";
- open(my $dbase, '+<dbase.mine') # ditto
+ open(my $dbase, "+<dbase.mine") # ditto
or die "Can't open 'dbase.mine' for update: $!";
- open(ARTICLE, '-|', "caesar <$article") # decrypt article
+ open(ARTICLE, "-|", "caesar <$article") # decrypt article
or die "Can't start caesar: $!";
open(ARTICLE, "caesar <$article |") # ditto
or die "Can't start sort: $!";
# in-memory files
- open(MEMORY,'>', \$var)
+ open(MEMORY, ">", \$var)
or die "Can't open memory file: $!";
print MEMORY "foo!\n"; # output will appear in $var
# process argument list of files along with any includes
foreach $file (@ARGV) {
- process($file, 'fh00');
+ process($file, "fh00");
}
sub process {
my($filename, $input) = @_;
$input++; # this is a string increment
- unless (open($input, $filename)) {
+ unless (open($input, "<", $filename)) {
print STDERR "Can't open $filename: $!\n";
return;
}
See L<perliol> for detailed info on PerlIO.
You may also, in the Bourne shell tradition, specify an EXPR beginning
-with C<< '>&' >>, in which case the rest of the string is interpreted
+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<< > >>,
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
-of IO buffers.) If you use the 3-arg form then you can pass either a
-number, the name of a filehandle or the normal "reference to a glob".
+of IO buffers.) If you use the three-argument
+form, then you can pass either a
+number, the name of a filehandle, or the normal "reference to a glob".
Here is a script that saves, redirects, and restores C<STDOUT> and
C<STDERR> using various methods:
#!/usr/bin/perl
- open my $oldout, ">&STDOUT" or die "Can't dup STDOUT: $!";
- open OLDERR, ">&", \*STDERR or die "Can't dup STDERR: $!";
+ open(my $oldout, ">&STDOUT") or die "Can't dup STDOUT: $!";
+ open(OLDERR, ">&", \*STDERR) or die "Can't dup STDERR: $!";
- open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!";
- open STDERR, ">&STDOUT" or die "Can't dup STDOUT: $!";
+ open(STDOUT, '>', "foo.out") or die "Can't redirect STDOUT: $!";
+ open(STDERR, ">&STDOUT") or die "Can't dup STDOUT: $!";
select STDERR; $| = 1; # make unbuffered
select STDOUT; $| = 1; # make unbuffered
print STDOUT "stdout 1\n"; # this works for
print STDERR "stderr 1\n"; # subprocesses too
- open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
- open STDERR, ">&OLDERR" or die "Can't dup OLDERR: $!";
+ open(STDOUT, ">&", $oldout) or die "Can't dup \$oldout: $!";
+ open(STDERR, ">&OLDERR") or die "Can't dup OLDERR: $!";
print STDOUT "stdout 2\n";
print STDERR "stderr 2\n";
Being parsimonious on filehandles is also useful (besides being
parsimonious) for example when something is dependent on file
descriptors, like for example locking using flock(). If you do just
-C<< open(A, '>>&B') >>, the filehandle A will not have the same file
-descriptor as B, and therefore flock(A) will not flock(B), and vice
-versa. But with C<< open(A, '>>&=B') >> the filehandles will share
-the same file descriptor.
-
-Note that if you are using Perls older than 5.8.0, Perl will be using
-the standard C libraries' fdopen() to implement the "=" functionality.
-On many Unix systems fdopen() fails when file descriptors exceed a
-certain value, typically 255. For Perls 5.8.0 and later, PerlIO is
-most often the default.
-
-You can see whether Perl has been compiled with PerlIO or not by
-running C<perl -V> and looking for C<useperlio=> line. If C<useperlio>
-is C<define>, you have PerlIO, otherwise you don't.
-
-If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>
-with 2-arguments (or 1-argument) form of open(), then
-there is an implicit fork done, and the return value of open is the pid
-of the child within the parent process, and C<0> within the child
-process. (Use C<defined($pid)> to determine whether the open was successful.)
+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.
+
+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.
+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.
+
+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
+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: $!";
+
+or
+
+ $child_pid = open(TO_KID, "|-") // die "can't fork: $!";
+
+followed by
+
+ if ($child_pid) {
+ # am the parent:
+ # either write TO_KID or else read FROM_KID
+ ...
+ wait $child_pid;
+ } else {
+ # am the child; use STDIN/STDOUT normally
+ ...
+ exit;
+ }
+
The filehandle behaves normally for the parent, but I/O to that
filehandle is piped from/to the STDOUT/STDIN of the child process.
In the child process, the filehandle isn't opened--I/O happens from/to
The following blocks are more or less equivalent:
open(FOO, "|tr '[a-z]' '[A-Z]'");
- open(FOO, '|-', "tr '[a-z]' '[A-Z]'");
- open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]';
- open(FOO, '|-', "tr", '[a-z]', '[A-Z]');
+ open(FOO, "|-", "tr '[a-z]' '[A-Z]'");
+ open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';
+ open(FOO, "|-", "tr", '[a-z]', '[A-Z]');
open(FOO, "cat -n '$file'|");
- open(FOO, '-|', "cat -n '$file'");
- open(FOO, '-|') || exec 'cat', '-n', $file;
- open(FOO, '-|', "cat", '-n', $file);
+ open(FOO, "-|", "cat -n '$file'");
+ open(FOO, "-|") || exec "cat", "-n", $file;
+ open(FOO, "-|", "cat", "-n", $file);
-The last two examples in each block shows the pipe as "list form", which is
+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 true C<fork()> (in other words, if your platform is
-Unix) you can use the list form.
+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
+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: $!";
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
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>.
+of
C<$^F>. See L<perlvar/$^F>.
Closing any piped filehandle causes the parent process to wait for the
-child to finish, and returns the status value in C<$?> and
+child to finish, then returns the status value in C<$?> and
C<${^CHILD_ERROR_NATIVE}>.
-The filename passed to 2-argument (or 1-argument) form of open() will
-have leading and trailing whitespace deleted, and the normal
+The filename passed to the one- and two-argument forms of open() 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: $!";
-Use 3-argument form to open a file with arbitrary weird characters in it,
+Use the three-argument form to open a file with arbitrary weird characters in it,
- open(FOO, '<', $file);
+ open(FOO, "<", $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");
+ open(FOO, "< $file\0")
+ || die "open failed: $!";
(this may not work on some bizarre filesystems). One should
-conscientiously choose between the I<magic> and 3-arguments form
+conscientiously choose between the I<magic> and I<three-argument> form
of open():
- open IN, $ARGV[0];
+ open(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];
+ open(IN, "<", $ARGV[0])
+ || die "can't open < $ARGV[0]: $!";
will have exactly the opposite restrictions.
-If you want a "real" C C<open> (see C<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 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:
use IO::Handle;
sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
Using the constructor from the C<IO::Handle> package (or one of its
subclasses, such as C<IO::File> or C<IO::Socket>), you can generate anonymous
-filehandles that have the scope of whatever variables hold references to
-them, and automatically close whenever and however you leave that scope:
+filehandles that have the scope of the variables used to hold them, then
+automatically (but silently) close once their reference counts become
+zero, typically at scope exit:
use IO::File;
#...
sub read_myfile_munged {
my $ALL = shift;
+ # or just leave it undef to autoviv
my $handle = IO::File->new;
- open($handle, "myfile") or die "myfile: $!";
+ open($handle, "<", "myfile") or die "myfile: $!";
$first = <$handle>
or return (); # Automatically closed here.
- mung $first or die "mung failed"; # Or here.
- return $first, <$handle> if $ALL; # Or here.
- $first; # Or here.
+ mung($first) or die "mung failed"; # Or here.
+ return (first, <$handle>) if $ALL; # Or here.
+ return $first; # Or here.
}
+B<WARNING:> The previous example has a bug because the automatic
+close that happens when the refcount on C<handle> does not
+properly detect and report failures. I<Always> close the handle
+yourself and inspect the return value.
+
+ close($handle)
+ || warn "close failed: $!";
+
See L</seek> for some details about mixing reading and writing.
+Portability issues: L<perlport/open>.
+
=item opendir DIRHANDLE,EXPR
X<opendir>
+=for Pod::Functions open a directory
+
Opens a directory named EXPR for processing by C<readdir>, C<telldir>,
C<seekdir>, C<rewinddir>, and C<closedir>. Returns true if successful.
DIRHANDLE may be an expression whose value can be used as an indirect
dirhandle, usually the real dirhandle name. If DIRHANDLE is an undefined
scalar variable (or array or hash element), the variable is assigned a
-reference to a new anonymous dirhandle.
+reference to a new anonymous dirhandle; that is, it's autovivified.
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
-See example at C<readdir>.
+See the example at C<readdir>.
=item ord EXPR
X<ord> X<encoding>
=item ord
-Returns the numeric (the native 8-bit encoding, like ASCII or EBCDIC,
-or Unicode) value of the first character of EXPR. If EXPR is an empty
-string, returns 0. If EXPR is omitted, uses C<$_>.
+=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<$_>.
+(Note I<character>, not byte.)
For the reverse, see L</chr>.
See L<perlunicode> for more about Unicode.
=item our TYPE EXPR : ATTRS
+=for Pod::Functions +5.6.0 declare and assign a package variable (lexical scoping)
+
C<our> associates a simple name with a package variable in the current
package for use within the current scope. When C<use strict 'vars'> is in
effect, C<our> lets you use declared global variables without qualifying
them with package names, within the lexical scope of the C<our> declaration.
-In this way C<our> differs from C<use vars>, which is package scoped.
+In this way C<our> differs from C<use vars>, which is package-scoped.
-Unlike C<my>, which both allocates storage for a variable and associates
-a simple name with that storage for use within the current scope, C<our>
-associates a simple name with a package variable in the current package,
-for use within the current scope. In other words, C<our> has the same
-scoping rules as C<my>, but does not necessarily create a
-variable.
+Unlike C<my> or C<state>, which allocates storage for a variable and
+associates a simple name with that storage for use within the current
+scope, C<our> associates a simple name with a package (read: global)
+variable in the current package, for use within the current lexical scope.
+In other words, C<our> has the same scoping rules as C<my> or C<state>, but
+does not necessarily create a variable.
If more than one value is listed, the list must be placed
in parentheses.
with it.
The exact semantics and interface of TYPE and ATTRS are still
-evolving. TYPE is currently bound to the use of 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
+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>.
=item pack TEMPLATE,LIST
X<pack>
+=for Pod::Functions convert a list into a binary representation
+
Takes a LIST of values and converts it into a string using the rules
given by the TEMPLATE. The resulting string is the concatenation of
the converted values. Typically, each converted value looks
A A text (ASCII) string, will be space padded.
Z A null-terminated (ASCIZ) string, will be null padded.
- b A bit string (ascending bit order inside each byte, like vec()).
+ b A bit string (ascending bit order inside each byte,
+ like vec()).
B A bit string (descending bit order inside each byte).
h A hex string (low nybble first).
H A hex string (high nybble first).
q A signed quad (64-bit) value.
Q An unsigned quad value.
- (Quads are available only if your system supports 64-bit
- integer values _and_ if Perl has been compiled to support those.
- Raises an exception otherwise.)
+ (Quads are available only if your system supports 64-bit
+ integer values _and_ if Perl has been compiled to support
+ those. Raises an exception otherwise.)
i A signed integer value.
I A unsigned integer value.
- (This 'integer' is _at_least_ 32 bits wide. Its exact
- size depends on what a local C compiler calls 'int'.)
+ (This 'integer' is _at_least_ 32 bits wide. Its exact
+ size depends on what a local C compiler calls 'int'.)
n An unsigned short (16-bit) in "network" (big-endian) order.
N An unsigned long (32-bit) in "network" (big-endian) order.
v An unsigned short (16-bit) in "VAX" (little-endian) order.
V An unsigned long (32-bit) in "VAX" (little-endian) order.
- j A Perl internal signed integer value (IV).
- J A Perl internal unsigned integer value (UV).
+ j A Perl internal signed integer value (IV).
+ J A Perl internal unsigned integer value (UV).
f A single-precision float in native format.
d A double-precision float in native format.
F A Perl internal floating-point value (NV) in native format
D A float of long-double precision in native format.
- (Long doubles are available only if your system supports long
- double values _and_ if Perl has been compiled to support those.
- Raises an exception otherwise.)
+ (Long doubles are available only if your system supports
+ long double values _and_ if Perl has been compiled to
+ support those. Raises an exception otherwise.)
p A pointer to a null-terminated string.
P A pointer to a structure (fixed-length string).
u A uuencoded string.
- U A Unicode character number. Encodes to a character in character mode
- and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in byte mode.
+ U A Unicode character number. Encodes to a character in char-
+ acter mode and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in
+ byte mode.
- w A BER compressed integer (not an ASN.1 BER, see perlpacktut for
- details). Its bytes represent an unsigned integer in base 128,
- most significant digit first, with as few digits as possible. Bit
- eight (the high bit) is set on each byte except the last.
+ w A BER compressed integer (not an ASN.1 BER, see perlpacktut
+ for details). Its bytes represent an unsigned integer in
+ base 128, most significant digit first, with as few digits
+ as possible. Bit eight (the high bit) is set on each byte
+ except the last.
x A null byte (a.k.a ASCII NUL, "\000", chr(0))
X Back up a byte.
@ Null-fill or truncate to absolute position, counted from the
start of the innermost ()-group.
- . Null-fill or truncate to absolute position specified by the value.
+ . Null-fill or truncate to absolute position specified by
+ the value.
( Start of a ()-group.
One or more modifiers below may optionally follow certain letters in the
nNvV Treat integers as signed instead of unsigned.
@. Specify position as byte offset in the internal
- representation of the packed string. Efficient but
- dangerous.
+ representation of the packed string. Efficient
+ but dangerous.
> sSiIlLqQ Force big-endian byte-order on the type.
jJfFdDpP (The "big end" touches the construct.)
in C<pack("C[80]", @arr)>. The repeat count gobbles that many values from
the LIST when used with all format types other than C<a>, C<A>, C<Z>, C<b>,
C<B>, C<h>, C<H>, C<@>, C<.>, C<x>, C<X>, and C<P>, where it means
-something else, dscribed below. Supplying a C<*> for the repeat count
+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
=item *
And if it's an integer I<n>, the offset is relative to the start of the
-I<n>th innermost C<()> group, or to the start of the string if I<n> is
+I<n>th innermost C<( )> group, or to the start of the string if I<n> is
bigger then the group level.
=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 *
The C<a>, C<A>, and C<Z> types gobble just one value, but pack it as a
string of length count, padding with nulls or spaces as needed. When
unpacking, C<A> strips trailing whitespace and nulls, C<Z> strips everything
-after the first null, and C<a> returns data without any sort of trimming.
+after the first null, and C<a> returns data with no stripping at all.
If the value to pack is too long, the result is truncated. If it's too
long and an explicit count is provided, C<Z> packs only C<$count-1> bytes,
followed by a null byte. Thus C<Z> always packs a trailing null, except
-for when the count is 0.
+when the count is 0.
=item *
Likewise, the C<b> and C<B> formats pack a string that's that many bits long.
-Each such format generates 1 bit of the result.
+Each such format generates 1 bit of the result. These are typically followed
+by a repeat count like C<B8> or C<B64>.
Each result bit is based on the least-significant bit of the corresponding
input character, i.e., on C<ord($char)%2>. In particular, characters C<"0">
If the input string is longer than needed, remaining characters are ignored.
A C<*> for the repeat count uses all characters of the input field.
-On unpacking, bits are converted to a string of C<"0">s and C<"1">s.
+On unpacking, bits are converted to a string of C<0>s and C<1>s.
=item *
The C<h> and C<H> formats pack a string that many nybbles (4-bit groups,
representable as hexadecimal digits, C<"0".."9"> C<"a".."f">) long.
-For each such format, pack() generates 4 bits of the result.
+For each such format, pack() generates 4 bits of result.
With non-alphabetical characters, the result is based on the 4 least-significant
bits of the input character, i.e., on C<ord($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>. Do not use any characters
-but these with this format.
+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
of characters is converted to 1 character of output. With format C<h>, the
within the structure itself as separate fields.
For C<pack>, you write I<length-item>C</>I<sequence-item>, and the
-I<length-item> describes how the length value is packed. Formats likely
+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
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
+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
-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
+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.
If I<sequence-item> refers to a string type (C<"A">, C<"a">, or C<"Z">),
an explicit repeat count for pack, the packed string is adjusted to that
length. For example:
- unpack("W/a", "\004Gurusamy") gives ("Guru")
- unpack("a3/A A*", "007 Bond J ") gives (" Bond", "J")
- unpack("a3 x2 /A A*", "007: Bond, J.") gives ("Bond, J", ".")
+ This code: gives this result:
+
+ unpack("W/a", "\004Gurusamy") ("Guru")
+ unpack("a3/A A*", "007 Bond J ") (" Bond", "J")
+ unpack("a3 x2 /A A*", "007: Bond, J.") ("Bond, J", ".")
- pack("n/a* w/a","hello,","world") gives "\000\006hello,\005world"
- pack("a/W2", ord("a") .. ord("z")) gives "2ab"
+ 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>.
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 used/uses them in
-little-endian mode, but SGI/Cray uses them in big-endian mode.
+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
egg-eating habits of the little-endian Lilliputians and the big-endian
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,
+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 endianness modifier:
+Here are some concerns to keep in mind when using an endianness modifier:
=over
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)
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
+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
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
+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 -ne 'printf "%v04X\n", $_ for unpack("C0A*", $_)'
+ 03B1.03C9
+ $ 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 -C0 -ne 'printf "%v02X\n", $_ for unpack("C0A*", $_)'
+ CE.B1.CF.89
+ $ 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.
+
=item *
You must yourself do any alignment or padding by inserting, for example,
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</>
template character. Within each repetition of a group, positioning with
-C<@> starts over at 0. Therefore, the result of
+C<@> starts over at 0. Therefore, the result of
pack("@1A((@2A)@3A)", qw[X Y Z])
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 pack() or unpack() a C structure like
struct {
char c; /* one signed, 8-bit character */
=item *
-If TEMPLATE requires more arguments that pack() is given, pack()
+If TEMPLATE requires more arguments than pack() is given, pack()
assumes additional C<""> arguments. If TEMPLATE requires fewer arguments
than given, extra arguments are ignored.
$foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
# same thing with Unicode circled letters.
$foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
- # same thing with Unicode circled letters. You don't get the UTF-8
- # bytes because the U at the start of the format caused a switch to
- # U0-mode, so the UTF-8 bytes get joined into characters
+ # same thing with Unicode circled letters. You don't get the
+ # UTF-8 bytes because the U at the start of the format caused
+ # a switch to U0-mode, so the UTF-8 bytes get joined into
+ # characters
$foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
# foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
- # This is the UTF-8 encoding of the string in the previous example
+ # This is the UTF-8 encoding of the string in the
+ # previous example
$foo = pack("ccxxcc",65,66,67,68);
# foo eq "AB\0\0CD"
The same template may generally also be used in unpack().
+=item package NAMESPACE
+
=item package NAMESPACE VERSION
X<package> X<module> X<namespace> X<version>
-=item package NAMESPACE
+=item package NAMESPACE BLOCK
=item package NAMESPACE VERSION BLOCK
X<package> X<module> X<namespace> X<version>
-=item package NAMESPACE BLOCK
+=for Pod::Functions declare a separate global namespace
-Declares the BLOCK, or the rest of the compilation unit, as being in
-the given namespace. The scope of the package declaration is either the
+Declares the BLOCK or the rest of the compilation unit as being in the
+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 the enclosing block, file, or eval (the same
-as the C<my> operator). All unqualified dynamic identifiers in this
-scope will be in the given namespace, except where overridden by another
-C<package> 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
+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> lexical variables, which are created
-with C<my> (or C<our> (or C<state>)). Typically it would be the first
+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
symbol table the compiler uses for the rest of that block. You can refer to
See L<perlmod/"Packages"> for more information about packages, modules,
and classes. See L<perlsub> for other scoping issues.
+=item __PACKAGE__
+X<__PACKAGE__>
+
+=for Pod::Functions +5.004 the current package
+
+A special token that returns the name of the package in which it occurs.
+
=item pipe READHANDLE,WRITEHANDLE
X<pipe>
+=for Pod::Functions open a pair of connected filehandles
+
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.
+Returns true on success.
+
See L<IPC::Open2>, L<IPC::Open3>, and
L<perlipc/"Bidirectional Communication with Another Process">
for examples of such things.
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>.
-=item pop ARRAY (or ARRAYREF)
+=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.
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>.
-If given a reference to an array, the argument will be dereferenced
-automatically.
+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:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
=item pos SCALAR
X<pos> X<match, position>
=item pos
+=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<$_> is used when the variable is not
-specified). Note that 0 is a valid match offset. C<undef> indicates
+specified). Note that 0 is a valid match offset. C<undef> indicates
that the search position is reset (usually due to match failure, but
can also be because no match has yet been run on the scalar).
C<pos> directly accesses the location used by the regexp engine to
store the offset, so assigning to C<pos> will change that offset, and
so will also influence the C<\G> zero-width assertion in regular
-expressions. Both of these effects take place for the next match, so
+expressions. Both of these effects take place for the next match, so
you can't affect the position with C<pos> during the current match,
such as in C<(?{pos() = 5})> or C<s//pos() = 5/e>.
+Setting C<pos> also resets the I<matched with zero-length> flag, described
+under L<perlre/"Repeated Patterns Matching a Zero-length Substring">.
+
Because a failed C<m//gc> match doesn't reset the offset, the return
from C<pos> won't change either in this case. See L<perlre> and
L<perlop>.
=item print FILEHANDLE LIST
X<print>
+=item print FILEHANDLE
+
=item print LIST
=item print
+=for Pod::Functions output a list to a filehandle
+
Prints a string or a list of strings. Returns true if successful.
-FILEHANDLE may be a scalar variable containing
-the name of or a reference to the filehandle, thus introducing
-one level of indirection. (NOTE: If FILEHANDLE is a variable and
-the next token is a term, it may be misinterpreted as an operator
-unless you interpose a C<+> or put parentheses around the arguments.)
-If FILEHANDLE is omitted, prints to standard output by default, or
-to the last selected output channel; see L</select>. If LIST is
-also omitted, prints C<$_> to the currently selected output handle.
-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, and any subroutine that you call will have one or more of
-its expressions evaluated in list context. Also 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 the arguments
+FILEHANDLE may be a scalar variable containing the name of or a reference
+to the filehandle, thus introducing one level of indirection. (NOTE: If
+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
+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
+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).
-Note that if you're storing FILEHANDLEs in an array, or if you're using
-any other expression more complex than a scalar variable to retrieve it,
-you will have to use a block returning the filehandle value instead:
+If you're storing handles in an array or hash, or in general whenever
+you're using any expression more complex than a bareword handle or a plain,
+unsubscripted scalar variable to retrieve it, you will have to use a block
+returning the filehandle value instead, in which case the LIST may not be
+omitted:
print { $files[$i] } "stuff\n";
print { $OK ? STDOUT : STDERR } "stuff\n";
=item printf FILEHANDLE FORMAT, LIST
X<printf>
+=item printf FILEHANDLE
+
=item printf FORMAT, LIST
+=item printf
+
+=for Pod::Functions output a formatted list to a filehandle
+
Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\>
-(the output record separator) is not appended. The first argument
-of the list will be interpreted as the C<printf> format. See C<sprintf>
-for an explanation of the format argument. If C<use locale> is in effect,
-and POSIX::setlocale() has been called, the character used for the decimal
+(the output record separator) is not appended. The first argument of the
+list will be interpreted as the C<printf> format. See
+L<sprintf|/sprintf FORMAT, LIST> for an
+explanation of the format argument. If you omit the LIST, C<$_> is used;
+to use FILEHANDLE without a LIST, you must use a real filehandle like
+C<FH>, not an indirect one like C<$fh>. If C<use locale> (including
+C<use locale ':not_characters'>) 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 LC_NUMERIC
-locale. See L<perllocale> and L<POSIX>.
+locale
setting. See L<perllocale> and L<POSIX>.
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
=item prototype FUNCTION
X<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
function has no prototype). FUNCTION is a reference to, or the name of,
the function whose prototype you want to retrieve.
does not really behave like a Perl function. Otherwise, the string
describing the equivalent prototype is returned.
-=item push ARRAY (or ARRAYREF),LIST
+=item push ARRAY,LIST
X<push> X<stack>
-Treats ARRAY as a stack, and pushes the values of LIST
-onto the end of ARRAY. The length of ARRAY increases by the length of
-LIST. Has the same effect as
+=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) {
$ARRAY[++$#ARRAY] = $value;
but is more efficient. Returns the number of elements in the array following
the completed C<push>.
-If given a reference to an array, the argument will be dereferenced
-automatically.
+Starting with Perl 5.14, C<push> can take a scalar EXPR, which must hold a
+reference to an unblessed array. The argument will be dereferenced
+automatically. This aspect of C<push> is considered highly experimental.
+The exact behaviour may change in a future version of Perl.
+
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
=item q/STRING/
+=for Pod::Functions singly quote a string
+
=item qq/STRING/
-=item qx/STRING/
+=for Pod::Functions doubly quote a string
=item qw/STRING/
+=for Pod::Functions quote a list of words
+
+=item qx/STRING/
+
+=for Pod::Functions backquote quote a string
+
Generalized quotes. See L<perlop/"Quote-Like Operators">.
=item qr/STRING/
+=for Pod::Functions +5.005 compile pattern
+
Regexp-like quote. See L<perlop/"Regexp Quote-Like Operators">.
=item quotemeta EXPR
=item quotemeta
-Returns the value of EXPR with all non-"word"
-characters backslashed. (That is, all characters not matching
+=for Pod::Functions quote regular expression magic characters
+
+Returns the value of EXPR with all the ASCII non-"word"
+characters backslashed. (That is, all ASCII characters not matching
C</[A-Za-z_0-9]/> will be preceded by a backslash in the
returned string, regardless of any locale settings.)
This is the internal function implementing
the C<\Q> escape in double-quoted strings.
+(See below for the behavior on non-ASCII code points.)
If EXPR is omitted, uses C<$_>.
quotemeta (and C<\Q> ... C<\E>) are useful when interpolating strings into
regular expressions, because by default an interpolated variable will be
-considered a mini-regular expression. For example:
+considered a mini-regular expression. For example:
my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
my $quoted_substring = quotemeta($substring);
$sentence =~ s{$quoted_substring}{big bad wolf};
-Will both leave the sentence as is. Normally, when accepting string input from
-the user, quotemeta() or C<\Q> must be used.
+Will both leave the sentence as is.
+Normally, when accepting literal string
+input from the user, quotemeta() 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.
+
+Starting in Perl v5.16, Perl adopted a Unicode-defined strategy for
+quoting non-ASCII characters; the quoting of ASCII characters is
+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
+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
+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
+considered to be word characters.
+
+Otherwise, Perl quotes non-ASCII characters using an adaptation from
+Unicode (see L<http://www.unicode.org/reports/tr31/>.)
+The only code points that are quoted are those that have any of the
+Unicode properties: Pattern_Syntax, Pattern_White_Space, White_Space,
+Default_Ignorable_Code_Point, or General_Category=Control.
+
+Of these properties, the two important ones are Pattern_Syntax and
+Pattern_White_Space. They have been set up by Unicode for exactly this
+purpose of deciding which characters in a regular expression pattern
+should be quoted. No character that can be in an identifier has these
+properties.
+
+Perl promises, that if we ever add regular expression pattern
+metacharacters to the dozen already defined
+(C<\ E<verbar> ( ) [ { ^ $ * + ? .>), that we will only use ones that have the
+Pattern_Syntax property. Perl also promises, that if we ever add
+characters that are considered to be white space in regular expressions
+(currently mostly affected by C</x>), they will all have the
+Pattern_White_Space property.
+
+Unicode promises that the set of code points that have these two
+properties will never change, so something that is not quoted in v5.16
+will never need to be quoted in any future Perl release. (Not all the
+code points that match Pattern_Syntax have actually had characters
+assigned to them; so there is room to grow, but they are quoted
+whether assigned or not. Perl, of course, would never use an
+unassigned code point as an actual metacharacter.)
+
+Quoting characters that have the other 3 properties is done to enhance
+the readability of the regular expression and not because they actually
+need to be quoted for regular expression purposes (characters with the
+White_Space property are likely to be indistinguishable on the page or
+screen from those with the Pattern_White_Space property; and the other
+two properties contain non-printing characters).
=item rand EXPR
X<rand> X<random>
=item rand
+=for Pod::Functions retrieve the next pseudorandom number
+
Returns a random fractional number greater than or equal to C<0> and less
than the value of EXPR. (EXPR should be positive.) If EXPR is
omitted, the value C<1> is used. Currently EXPR with the value C<0> is
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
+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,
+including: L<Data::Entropy>, L<Crypt::Random>, L<Math::Random::Secure>,
+and L<Math::TrulyRandom>.
+
=item read FILEHANDLE,SCALAR,LENGTH,OFFSET
X<read> X<file, read>
=item read FILEHANDLE,SCALAR,LENGTH
+=for Pod::Functions fixed-length buffered input from a filehandle
+
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
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 C<sysread>.
+fread(3) library function. To get a true 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
+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 UTF-8 encoded Unicode
+pragma, L<open>), the I/O will operate on UTF8-encoded Unicode
characters, not bytes. Similarly for the C<:encoding> pragma:
in that case pretty much any characters can be read.
=item readdir DIRHANDLE
X<readdir>
+=for Pod::Functions get a directory from a directory handle
+
Returns the next directory entry for a directory opened by C<opendir>.
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
}
closedir $dh;
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious failures, 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 5.012; # so readdir assigns to $_ in a lone while test
+
=item readline EXPR
=item readline
X<readline> X<gets> X<fgets>
+=for Pod::Functions fetch a record from a file
+
Reads from the filehandle whose typeglob is contained in EXPR (or from
-*ARGV if EXPR is not provided). In scalar context, each call reads and
+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"
}
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> filehandle. In that case, you have to open each element of
C<@ARGV> yourself since C<eof> handles C<ARGV> differently.
foreach my $arg (@ARGV) {
=item readlink
+=for Pod::Functions determine where a symbolic link is pointing
+
Returns the value of a symbolic link, if symbolic links are
implemented. If not, raises an exception. If there is a system
error, returns the undefined value and sets C<$!> (errno). If EXPR is
omitted, uses C<$_>.
+Portability issues: L<perlport/readlink>.
+
=item readpipe EXPR
=item readpipe
X<readpipe>
+=for Pod::Functions execute a system command and collect standard output
+
EXPR is executed as a system command.
The collected standard output of the command is returned.
In scalar context, it comes back as a single (potentially
=item recv SOCKET,SCALAR,LENGTH,FLAGS
X<recv>
+=for Pod::Functions receive a message over a Socket
+
Receives a message on a socket. Attempts to receive LENGTH characters
of data into variable SCALAR from the specified SOCKET filehandle.
SCALAR will be grown or shrunk to the length actually read. Takes the
(8-bit) bytes or characters are received. By default all sockets
operate on bytes, but for example if the socket has been changed using
binmode() to operate with the C<:encoding(utf8)> I/O layer (see the
-C<open> pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode
+C<open> pragma, L<open>), the I/O will operate on UTF8-encoded Unicode
characters, not bytes. Similarly for the C<:encoding> pragma: in that
case pretty much any characters can be read.
=item redo
+=for Pod::Functions start this loop iteration over again
+
The C<redo> command restarts the loop block without evaluating the
conditional again. The C<continue> block, if any, is not executed. If
the LABEL is omitted, the command refers to the innermost enclosing
}
C<redo> cannot be used to retry a block that returns a value such as
-C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
+C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit
a grep() or map() operation.
Note that a block by itself is semantically identical to a loop
=item ref
+=for Pod::Functions find out the type of thing being referenced
+
Returns a non-empty string if EXPR is a reference, the empty
-string otherwise. If EXPR
+string otherwise. If EXPR
is not specified, C<$_> will be used. The value returned depends on the
type of thing the reference is a reference to.
Builtin types include:
}
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
+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">.
The result C<Regexp> indicates that the argument is a regular expression
=item rename OLDNAME,NEWNAME
X<rename> X<move> X<mv> X<ren>
+=for Pod::Functions change a filename
+
Changes the name of a file; an existing file NEWNAME will be
clobbered. Returns true for success, false otherwise.
For a platform independent C<move> function look at the L<File::Copy>
module.
+Portability issues: L<perlport/rename>.
+
=item require VERSION
X<require>
=item require
+=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<$_> if EXPR is not supplied.
Now that you understand how C<require> looks for files with a
bareword argument, there is a little extra functionality going on behind
the scenes. Before C<require> looks for a "F<.pm>" extension, it will
-first look for a similar filename with a "F<.pmc>" extension. If this file
+first look for a similar filename with a "F<.pmc>" extension. If this file
is found, it will be loaded in place of any file ending in a "F<.pm>"
extension.
-You can also insert hooks into the import facility, by putting Perl code
+You can also insert hooks into the import facility by putting Perl code
directly into the @INC array. There are three forms of hooks: subroutine
-references, array references and blessed objects.
+references, array references, and blessed objects.
Subroutine references are the simplest case. When the inclusion system
walks through @INC and encounters a subroutine, this subroutine gets
=item 2
-A reference to a subroutine. If there is no filehandle (previous item),
+A reference to a subroutine. If there is no filehandle (previous item),
then this subroutine is expected to generate one line of source code per
-call, writing the line into C<$_> and returning 1, then returning 0 at
-end of file. If there is a filehandle, then the subroutine will be
+call, writing the line into C<$_> and returning 1, then finally at end of
+file returning 0. If there is a filehandle, then the subroutine will be
called to act as a simple source filter, with the line as read in C<$_>.
Again, return 1 for each valid line, and 0 after all lines have been
returned.
=item 3
-Optional state for the subroutine. The state is passed in as C<$_[1]>. A
+Optional state for the subroutine. The state is passed in as C<$_[1]>. A
reference to the subroutine itself is passed in as C<$_[0]>.
=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.
Note that this filehandle must be a real filehandle (strictly a typeglob
-or reference to a typeglob, blessed or unblessed); tied filehandles will be
-ignored and return value processing will stop there.
+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
reference. This subroutine is called as above, but the first parameter is
push @INC, Foo->new(...);
These hooks are also permitted to set the %INC entry
-corresponding to the files they have loaded. See L<perlvar/%INC>.
+corresponding to the files they have loaded.
See L<perlvar/%INC>.
For a yet-more-powerful import facility, see L</use> and L<perlmod>.
=item 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
expression is interpreted as a list of single characters (hyphens
=item return
+=for Pod::Functions get out of a function early
+
Returns from a subroutine, C<eval>, or C<do FILE> 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 C<wantarray>). If no EXPR
+may vary from one execution to the next (see L</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.
=item reverse LIST
X<reverse> X<rev> X<invert>
+=for Pod::Functions flip a string or a list
+
In list context, returns a list value consisting of the elements
of LIST in the opposite order. In scalar context, concatenates the
elements of LIST and returns a string value with all characters
=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.
+Portability issues: L<perlport/rewinddir>.
+
=item rindex STR,SUBSTR,POSITION
X<rindex>
=item rindex STR,SUBSTR
+=for Pod::Functions right-to-left substring search
+
Works just like index() 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.
=item rmdir
+=for Pod::Functions remove a directory
+
Deletes the directory specified by FILENAME if that directory is
-empty. If it succeeds it returns true, otherwise it returns false and
+empty. If it succeeds it returns true; otherwise it returns false and
sets C<$!> (errno). If FILENAME is omitted, uses C<$_>.
To remove a directory tree recursively (C<rm -rf> on Unix) look at
=item s///
+=for Pod::Functions replace a pattern with a string
+
The substitution operator. See L<perlop/"Regexp Quote-Like Operators">.
=item say FILEHANDLE LIST
X<say>
+=item say FILEHANDLE
+
=item say LIST
=item say
-Just like C<print>, but implicitly appends a newline.
-C<say LIST> is simply an abbreviation for C<{ local $\ = "\n"; print
-LIST }>.
+=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>.
-This keyword is available only when the "say" feature is
-enabled: see L<feature>.
+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.
=item scalar EXPR
X<scalar> X<context>
+=for Pod::Functions force a scalar context
+
Forces EXPR to be interpreted in scalar context and returns the value
of EXPR.
the construction C<@{[ (some expression) ]}>, but usually a simple
C<(some expression)> suffices.
-Because C<scalar> is a unary operator, if you accidentally use for EXPR a
-parenthesized list, 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.
+Because C<scalar> 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:
=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>.
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
-POSITION, and C<2> to set it to EOF plus POSITION (typically
-negative). For WHENCE you may use the constants C<SEEK_SET>,
+I<in bytes> to POSITION; C<1> to set it to the current position plus
+POSITION; and C<2> to set it to EOF plus POSITION, typically
+negative. For WHENCE you may 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. Returns C<1> on success, C<0>
+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
=item seekdir DIRHANDLE,POS
X<seekdir>
+=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
=item select
+=for Pod::Functions reset default output or do I/O multiplexing
+
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 will
+effects: first, a C<write> or a C<print> without a filehandle
default to this FILEHANDLE. Second, references to variables related to
-output will refer to this output channel. For example, if you have to
-set the top of form format for more than one output channel, you might
-do the following:
+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:
select(REPORT1);
$^ = 'report1_top';
use IO::Handle;
STDERR->autoflush(1);
+Portability issues: L<perlport/select>.
+
=item select RBITS,WBITS,EBITS,TIMEOUT
X<select>
can be constructed using C<fileno> and C<vec>, along these lines:
$rin = $win = $ein = '';
- vec($rin,fileno(STDIN),1) = 1;
- vec($win,fileno(STDOUT),1) = 1;
+ vec($rin, fileno(STDIN), 1) = 1;
+ vec($win, fileno(STDOUT), 1) = 1;
$ein = $rin | $win;
If you want to select on many filehandles, you may wish to write a
subroutine like this:
sub fhbits {
- my(@fhlist) = split(' ',$_[0]);
- my($bits);
- for (@fhlist) {
- vec($bits,fileno($_),1) = 1;
+ my @fhlist = @_;
+ my $bits = "";
+ for my $fh (@fhlist) {
+ vec($bits, fileno($fh), 1) = 1;
}
- $bits;
+ return $bits;
}
- $rin = fhbits('STDIN TTY SOCK');
+ $rin = fhbits(*STDIN, *TTY, *MYSOCK);
The usual idiom is:
is implementation-dependent. See also L<perlport> for notes on the
portability of C<select>.
-On error, C<select> behaves like select(2): it returns
+On error, C<select> behaves just like select(2): it returns
-1 and sets C<$!>.
-On some Unixes, select(2) may report a socket file
-descriptor as "ready for reading" when no data is available, and
-thus a subsequent read blocks. 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, 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.
+
+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.
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.
+Portability issues: L<perlport/select>.
+
=item semctl ID,SEMNUM,CMD,ARG
X<semctl>
+=for Pod::Functions SysV semaphore control operations
+
Calls the System V IPC function semctl(2). You'll probably have to say
use IPC::SysV;
See also L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::Semaphore>
documentation.
+Portability issues: L<perlport/semctl>.
+
=item semget KEY,NSEMS,FLAGS
X<semget>
+=for Pod::Functions get set of SysV semaphores
+
Calls the System V IPC function semget(2). Returns the semaphore id, or
-the undefined value if there is an error. See also
+the undefined value on error. See also
L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::SysV::Semaphore>
documentation.
+Portability issues: L<perlport/semget>.
+
=item semop KEY,OPSTRING
X<semop>
+=for Pod::Functions SysV semaphore operations
+
Calls the System V IPC function 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
implies the number of semaphore operations. Returns true if
-successful, or false if there is an error. As an example, the
+successful, false on error. As an example, the
following code waits on semaphore $semnum of semaphore id $semid:
$semop = pack("s!3", $semnum, -1, 0);
L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::SysV::Semaphore>
documentation.
+Portability issues: L<perlport/semop>.
+
=item send SOCKET,MSG,FLAGS,TO
X<send>
=item send SOCKET,MSG,FLAGS
+=for Pod::Functions send a message over a socket
+
Sends a message on a socket. Attempts to send the scalar MSG to the SOCKET
filehandle. Takes the same flags as the system call of the same name. On
unconnected sockets, you must specify a destination to I<send to>, in which
=item setpgrp PID,PGRP
X<setpgrp> X<group>
+=for Pod::Functions set the process group of a process
+
Sets the current process group for the specified PID, C<0> for the current
process. Raises an exception when used on a machine that doesn't
implement POSIX setpgid(2) or BSD setpgrp(2). If the arguments are omitted,
accept any arguments, so only C<setpgrp(0,0)> is portable. See also
C<POSIX::setsid()>.
+Portability issues: L<perlport/setpgrp>.
+
=item setpriority WHICH,WHO,PRIORITY
X<setpriority> X<priority> X<nice> X<renice>
+=for Pod::Functions set a process's nice value
+
Sets the current priority for a process, a process group, or a user.
(See setpriority(2).) Raises an exception when used on a machine
that doesn't implement setpriority(2).
+Portability issues: L<perlport/setpriority>.
+
=item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
X<setsockopt>
-Sets the socket option requested. Returns undefined if there is an
-error. Use integer constants provided by the C<Socket> module for
+=for Pod::Functions set some socket options
+
+Sets the socket option requested. Returns C<undef> on error.
+Use integer constants provided by the C<Socket> module for
LEVEL and OPNAME. Values for LEVEL can also be obtained from
getprotobyname. OPTVAL might either be a packed string or an integer.
An integer OPTVAL is shorthand for pack("i", OPTVAL).
use Socket qw(IPPROTO_TCP TCP_NODELAY);
setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1);
-=item shift ARRAY (or ARRAYREF)
+Portability issues: L<perlport/setsockopt>.
+
+=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
established by the C<eval STRING>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>,
-C<UNITCHECK {}> and C<END {}> constructs.
+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.
+
+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:
-If given a reference to an array, the argument will be dereferenced
-automatically.
+ 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
=item shmctl ID,CMD,ARG
X<shmctl>
+=for Pod::Functions SysV shared memory operations
+
Calls the System V IPC function shmctl. 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<shmid_ds>
-structure. Returns like ioctl: the undefined value for error, "C<0> but
-true" for zero, or the actual return value otherwise.
+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.
+Portability issues: L<perlport/shmctl>.
+
=item shmget KEY,SIZE,FLAGS
X<shmget>
+=for Pod::Functions get SysV shared memory segment identifier
+
Calls the System V IPC function shmget. Returns the shared memory
-segment id, or the undefined value if there is an error.
+segment id, or C<undef> on error.
See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
+Portability issues: L<perlport/shmget>.
+
=item shmread ID,VAR,POS,SIZE
X<shmread>
X<shmwrite>
+=for Pod::Functions read SysV shared memory
+
=item shmwrite ID,STRING,POS,SIZE
+=for Pod::Functions write SysV shared memory
+
Reads or writes the System V shared memory segment ID starting at
position POS for size SIZE by attaching to it, copying in/out, and
detaching from it. When reading, VAR must be a variable that will
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, or false if there is an error.
-shmread() taints the variable. See also L<perlipc/"SysV IPC">,
-C<IPC::SysV> documentation, and the C<IPC::Shareable> module from CPAN.
+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.
+
+Portability issues: L<perlport/shmread> and L<perlport/shmwrite>.
=item shutdown SOCKET,HOW
X<shutdown>
+=for Pod::Functions close down just half of a socket connection
+
Shuts down a socket connection in the manner indicated by HOW, which
has the same interpretation as in the syscall of the same name.
=item sin
+=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<$_>.
=item sleep
+=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.
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.
+your system supports it.
See L<perlfaq8> for details.
See also the POSIX module's C<pause> function.
=item socket SOCKET,DOMAIN,TYPE,PROTOCOL
X<socket>
+=for Pod::Functions create a socket
+
Opens a socket of the specified kind and attaches it to filehandle
SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for
the syscall of the same name. You should C<use Socket> first
=item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
X<socketpair>
+=for Pod::Functions create a pair of sockets
+
Creates an unnamed pair of sockets in the specified domain, of the
specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as
for the syscall of the same name. If unimplemented, raises an exception.
emulate socketpair using IP sockets to localhost if your system implements
sockets but not socketpair.
+Portability issues: L<perlport/socketpair>.
+
=item sort SUBNAME LIST
X<sort> X<qsort> X<quicksort> X<mergesort>
=item sort LIST
+=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.
subroutine to use. In place of a SUBNAME, you can provide a BLOCK as
an anonymous, in-line sort subroutine.
-If the subroutine's prototype is C<($$)>, the elements to be compared
-are passed by reference in C<@_>, as for a normal subroutine. This is
-slower than unprototyped subroutines, where the elements to be
-compared are passed into the subroutine
-as the package global variables $a and $b (see example below). Note that
-in the latter case, it is usually counter-productive to declare $a and
-$b as lexicals.
+If the subroutine's prototype is C<($$)>, 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.
+
+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 $b are
+not set.
The values to be compared are always passed by reference and should not
be modified.
You also cannot exit out of the sort block or subroutine using any of the
loop control operators described in L<perlsyn> or with C<goto>.
-When C<use locale> is in effect, C<sort LIST> sorts LIST according to the
+When C<use locale> (but not C<use locale 'not_characters'>) is in
+effect, C<sort LIST> sorts LIST according to the
current collation locale. See L<perllocale>.
sort() returns aliases into the original list, much as a for loop's index
something to be avoided when writing clear code.
Perl 5.6 and earlier used a quicksort algorithm to implement sort.
-That algorithm was not stable, and I<could> go quadratic. (A I<stable> sort
+That algorithm was not stable, so I<could> go quadratic. (A I<stable> sort
preserves the input order of elements that compare equal. Although
quicksort's run time is O(NlogN) when averaged over all arrays of
length N, the time can be O(N**2), I<quadratic> behavior, for some
@articles = sort {$a cmp $b} @files;
# now case-insensitively
- @articles = sort {uc($a) cmp uc($b)} @files;
+ @articles = sort {fc($a) cmp fc($b)} @files;
# same thing in reversed order
@articles = sort {$b cmp $a} @files;
# sort using explicit subroutine name
sub byage {
- $age{$a} <=> $age{$b}; # presuming numeric
+ $age{$a} <=> $age{$b}; # presuming numeric
}
@sortedclass = sort byage @class;
my @new = sort {
($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
- ||
- uc($a) cmp uc($b)
+ ||
+ fc($a) cmp fc($b)
} @old;
# same thing, but much more efficiently;
my @nums = @caps = ();
for (@old) {
push @nums, ( /=(\d+)/ ? $1 : undef );
- push @caps, uc($_);
+ push @caps, fc($_);
}
my @new = @old[ sort {
- $nums[$b] <=> $nums[$a]
- ||
- $caps[$a] cmp $caps[$b]
- } 0..$#old
- ];
+ $nums[$b] <=> $nums[$a]
+ ||
+ $caps[$a] cmp $caps[$b]
+ } 0..$#old
+ ];
# same thing, but without any temps
@new = map { $_->[0] }
sort { $b->[1] <=> $a->[1]
- ||
- $a->[2] cmp $b->[2]
- } map { [$_, /=(\d+)/, uc($_)] } @old;
+ ||
+ $a->[2] cmp $b->[2]
+ } map { [$_, /=(\d+)/, fc($_)] } @old;
# using a prototype allows you to use any comparison subroutine
# as a sort subroutine (including other package's subroutines)
@new = sort { substr($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
+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;
well-defined.
Because C<< <=> >> returns C<undef> when either operand is C<NaN>
-(not-a-number), and because C<sort> raises an exception unless the
-result of a comparison is defined, when sorting with a comparison function
-like C<< $a <=> $b >>, be careful about lists that might contain a C<NaN>.
-The following example takes advantage that C<NaN != NaN> to
+(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;
-=item splice ARRAY (or ARRAYREF),OFFSET,LENGTH,LIST
+=item splice ARRAY or EXPR,OFFSET,LENGTH,LIST
X<splice>
-=item splice ARRAY (or ARRAYREF),OFFSET,LENGTH
+=item splice ARRAY or EXPR,OFFSET,LENGTH
+
+=item splice ARRAY or EXPR,OFFSET
-=item splice ARRAY (or ARRAYREF),OFFSET
+=item splice ARRAY or EXPR
-=item splice ARRAY (or ARRAYREF)
+=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,
If LENGTH is omitted, removes everything from OFFSET onward.
If LENGTH is negative, removes the elements from OFFSET onward
except for -LENGTH elements at the end of the array.
-If both OFFSET and LENGTH are omitted, removes everything. If OFFSET is
+If both OFFSET and LENGTH are omitted, removes everything. If OFFSET is
past the end of the array, Perl issues a warning, and splices at the
end of the array.
-If given a reference to an array, the argument will be dereferenced
-automatically.
-
-The following equivalences hold (assuming C<< $[ == 0 and $#a >= $i >> )
+The following equivalences hold (assuming C<< $#a >= $i >> )
push(@a,$x,$y) splice(@a,@a,0,$x,$y)
pop(@a) splice(@a,-1)
}
if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }
+Starting with Perl 5.14, C<splice> can take scalar EXPR, which must hold a
+reference to an unblessed array. The argument will be dereferenced
+automatically. This aspect of C<splice> is considered highly experimental.
+The exact behaviour may change in a future version of Perl.
+
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
=item split /PATTERN/,EXPR,LIMIT
X<split>
=item split
-Splits the string EXPR into a list of strings and returns that list. By
-default, empty leading fields are preserved, and empty trailing ones are
-deleted. (If all fields are empty, they are considered to be trailing.)
+=for Pod::Functions split up a string using a regexp delimiter
+
+Splits the string EXPR into a list of strings and returns the
+list in list context, or the size of the list in scalar context.
+
+If only PATTERN is given, EXPR defaults to C<$_>.
+
+Anything in EXPR that matches PATTERN is taken to be a separator
+that separates the EXPR into substrings (called "I<fields>") that
+do B<not> include the separator. Note that a separator may be
+longer than one character or even have no characters at all (the
+empty string, which is a zero-width match).
+
+The PATTERN need not be constant; an expression may be used
+to specify a pattern that varies at runtime.
+
+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";
+
+uses the 'b' in 'abc' as a separator to produce the output 'a:c'.
+However, this:
+
+ print join(':', split('', 'abc')), "\n";
-In scalar context, returns the number of fields found.
+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
+list of its component characters.
-If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted,
-splits on whitespace (after skipping any leading whitespace). Anything
-matching PATTERN is taken to be a delimiter separating the fields. (Note
-that the delimiter may be longer than one character.)
+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
+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
+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
+I<any> contiguous whitespace (not just a single space character) is used as
+a separator. However, this special treatment can be avoided by specifying
+the pattern S<C</ />> instead of the string S<C<" ">>, thereby allowing
+only a single space character to be a separator.
+
+If omitted, PATTERN defaults to a single space, S<C<" ">>, triggering
+the previously described I<awk> emulation.
If LIMIT is specified and positive, it represents the maximum number
-of fields the EXPR will be split into, though the actual number of
-fields returned depends on the number of times PATTERN matches within
-EXPR. If LIMIT is unspecified or zero, trailing null fields are
-stripped (which potential users of C<pop> would do well to remember).
-If LIMIT is negative, it is treated as if an arbitrarily large LIMIT
-had been specified. Note that splitting an EXPR that evaluates to the
-empty string always returns the empty list, regardless of the LIMIT
-specified.
+of fields into which the EXPR may be split; in other words, LIMIT is
+one greater than the maximum number of times EXPR may be split. Thus,
+the LIMIT value C<1> means that EXPR may be split a maximum of zero
+times, producing a maximum of one field (namely, the entire value of
+EXPR). For instance:
-A pattern matching the empty string (not to be confused with
-an empty pattern C<//>, which is just one member of the set of patterns
-matching the epmty string), splits EXPR into individual
-characters. For example:
+ print join(':', split(//, 'abc', 1)), "\n";
- print join(':', split(/ */, 'hi there')), "\n";
+produces the output 'abc', and this:
-produces the output 'h:i:t:h:e:r:e'.
+ print join(':', split(//, 'abc', 2)), "\n";
-As a special case for C<split>, the empty pattern C<//> specifically
-matches the empty string; this is not be confused with the normal use
-of an empty pattern to mean the last successful match. So to split
-a string into individual characters, the following:
+produces the output 'a:bc', and each of these:
- print join(':', split(//, 'hi there')), "\n";
+ print join(':', split(//, 'abc', 3)), "\n";
+ print join(':', split(//, 'abc', 4)), "\n";
-produces the output 'h:i: :t:h:e:r:e'.
+produces the output 'a:b:c'.
-Empty leading fields are produced when there are positive-width matches at
-the beginning of the string; a zero-width match at the beginning of
-the string does not produce an empty field. For example:
+If LIMIT is negative, it is treated as if it were instead arbitrarily
+large; as many fields as possible are produced.
- print join(':', split(/(?=\w)/, 'hi there!'));
+If LIMIT is omitted (or, equivalently, zero), then it is usually
+treated as if it were instead negative but with the exception that
+trailing empty fields are stripped (empty leading fields are always
+preserved); if all fields are empty, then all fields are considered to
+be trailing (and are thus stripped in this case). Thus, the following:
-produces the output 'h:i :t:h:e:r:e!'. Empty trailing fields, on the other
-hand, are produced when there is a match at the end of the string (and
-when LIMIT is given and is not 0), regardless of the length of the match.
-For example:
+ print join(':', split(',', 'a,b,c,,,')), "\n";
- print join(':', split(//, 'hi there!', -1)), "\n";
- print join(':', split(/\W/, 'hi there!', -1)), "\n";
+produces the output 'a:b:c', but the following:
-produce the output 'h:i: :t:h:e:r:e:!:' and 'hi:there:', respectively,
-both with an empty trailing field.
+ print join(':', split(',', 'a,b,c,,,', -1)), "\n";
-The LIMIT parameter can be used to split a line partially
+produces the output 'a:b:c:::'.
- ($login, $passwd, $remainder) = split(/:/, $_, 3);
+In time-critical applications, it is worthwhile to avoid splitting
+into more fields than necessary. Thus, when assigning to a list,
+if LIMIT is omitted (or zero), then LIMIT is treated as though it
+were one larger than the number of variables in the list; for the
+following, LIMIT is implicitly 4:
-When assigning to a list, if LIMIT is omitted, or zero, Perl supplies
-a LIMIT one larger than the number of variables in the list, to avoid
-unnecessary work. For the list above LIMIT would have been 4 by
-default. In time critical applications it behooves you not to split
-into more fields than you really need.
+ ($login, $passwd, $remainder) = split(/:/);
-If the PATTERN contains parentheses, additional list elements are
-created from each matching substring in the delimiter.
+Note that splitting an EXPR that evaluates to the empty string always
+produces zero fields, regardless of the LIMIT specified.
- split(/([,-])/, "1-10,20", 3);
+An empty leading field is produced when there is a positive-width
+match at the beginning of EXPR. For instance:
-produces the list value
+ print join(':', split(/ /, ' abc')), "\n";
- (1, '-', 10, ',', 20)
+produces the output ':abc'. However, a zero-width match at the
+beginning of EXPR never produces an empty field, so that:
-If you had the entire header of a normal Unix email message in $header,
-you could split it up into fields and their values this way:
+ print join(':', split(//, ' abc'));
- $header =~ s/\n(?=\s)//g; # fix continuation lines
- %hdrs = (UNIX_FROM => split /^(\S*?):\s*/m, $header);
+produces the output S<' :a:b:c'> (rather than S<': :a:b:c'>).
-The pattern C</PATTERN/> may be replaced with an expression to specify
-patterns that vary at runtime. (To do runtime compilation only once,
-use C</$variable/o>.)
+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
+(of course, unless a non-zero LIMIT is given explicitly, such fields are
+removed, as in the last example). Thus:
-As a special case, specifying a PATTERN of space (S<C<' '>>) will split on
-white space just as C<split> with no arguments does. Thus, S<C<split(' ')>> can
-be used to emulate B<awk>'s default behavior, whereas S<C<split(/ /)>>
-will give you as many initial null fields (empty string) as there are leading spaces.
-A C<split> on C</\s+/> is like a S<C<split(' ')>> except that any leading
-whitespace produces a null first field. A C<split> with no arguments
-really does a S<C<split(' ', $_)>> internally.
+ print join(':', split(//, ' abc', -1)), "\n";
-A PATTERN of C</^/> is treated as if it were C</^/m>, since it isn't
-much use otherwise.
+produces the output S<' :a:b:c:'>.
-Example:
+If the PATTERN contains
+L<capturing groups|perlretut/Grouping things and hierarchical matching>,
+then for each separator, an additional field is produced for each substring
+captured by a group (in the order in which the groups are specified,
+as per L<backreferences|perlretut/Backreferences>); if any group does not
+match, then it captures the C<undef> value instead of a substring. Also,
+note that any such additional field is produced whenever there is a
+separator (that is, whenever a split occurs), and such an additional field
+does B<not> count towards the LIMIT. Consider the following expressions
+evaluated in list context (each returned list is provided in the associated
+comment):
- open(PASSWD, '/etc/passwd');
- while (<PASSWD>) {
- chomp;
- ($login, $passwd, $uid, $gid,
- $gcos, $home, $shell) = split(/:/);
- #...
- }
+ split(/-|,/, "1-10,20", 3)
+ # ('1', '10', '20')
+
+ split(/(-|,)/, "1-10,20", 3)
+ # ('1', '-', '10', ',', '20')
-As with regular pattern matching, any capturing parentheses that are not
-matched in a C<split()> will be set to C<undef> when returned:
+ split(/-|(,)/, "1-10,20", 3)
+ # ('1', undef, '10', ',', '20')
- @fields = split /(A)|B/, "1A2B3";
- # @fields is (1, 'A', 2, undef, 3)
+ split(/(-)|,/, "1-10,20", 3)
+ # ('1', '-', '10', undef, '20')
+
+ split(/(-)|(,)/, "1-10,20", 3)
+ # ('1', '-', undef, '10', undef, ',', '20')
=item sprintf FORMAT, LIST
X<sprintf>
+=for Pod::Functions formatted print into a string
+
Returns a string formatted by the usual C<printf> conventions of the C
library function C<sprintf>. See below for more details
-and see
C<sprintf(3)> or C<printf(3)> on your system for an explanation of
+and see
L<sprintf(3)> or L<printf(3)> on your system for an explanation of
the general principles.
For example:
therefore unavailable from Perl.
Unlike C<printf>, C<sprintf> does not do what you probably mean when you
-pass it an array as your first argument. The array is given scalar context,
+pass it an array as your first argument.
+The array is given scalar context,
and instead of using the 0th element of the array as the format, Perl will
use the count of elements in the array as the format, which is almost never
useful.
%B like %b, but using an upper-case "B" with the # flag
%p a pointer (outputs the Perl value's address in hexadecimal)
%n special: *stores* the number of characters output so far
- into the next variable in the parameter list
+ into the next argument in the parameter list
Finally, for backward (and we do mean "backward") compatibility, Perl
permits these unnecessary but widely-supported conversions:
=item format parameter index
-An explicit format parameter index, such as C<2$>. By default sprintf
+An explicit format parameter index, such as C<2$>. By default sprintf
will format the next unused argument in the list, but this allows you
to take the arguments out of order:
=item vector flag
This flag tells Perl to interpret the supplied string as a vector of
-integers, one for each character in the string. Perl applies the format to
+integers, one for each character in the string. Perl applies the format to
each integer in turn, then joins the resulting strings with a separator (a
-dot C<.> by default). This can be useful for displaying ordinal values of
+dot C<.> by default). This can be useful for displaying ordinal values of
characters in arbitrary strings:
printf "%vd", "AB\x{100}"; # prints "65.66.256"
=item (minimum) width
Arguments are usually formatted to be only as wide as required to
-display the given value. You can override the width by putting
+display the given value. You can override the width by putting
a number here, or get the width from the next argument (with C<*>)
or from a specified argument (e.g., with C<*2$>):
- printf
'<%s>', "a"; # prints "<a>"
- printf '<%6s>', "a"; # prints "< a>"
- printf '<%*s>', 6, "a"; # prints "< a>"
- printf '<%*2$s>', "a", 6; # prints "< a>"
- printf '<%2s>', "long"; # prints "<long>" (does not truncate)
+ printf
"<%s>", "a"; # prints "<a>"
+ printf "<%6s>", "a"; # prints "< a>"
+ printf "<%*s>", 6, "a"; # prints "< a>"
+ printf "<%*2$s>", "a", 6; # prints "< a>"
+ printf "<%2s>", "long"; # prints "<long>" (does not truncate)
If a field width obtained through C<*> is negative, it has the same
effect as the C<-> flag: left-justification.
You can specify a precision (for numeric conversions) or a maximum
width (for string conversions) by specifying a C<.> followed by a number.
-For floating-point formats except 'g' and 'G', this specifies
+For floating-point formats except C<g> and C<G>, this specifies
how many places right of the decimal point to show (the default being 6).
For example:
printf '<%.1e>', 10; # prints "<1.0e+01>"
For "g" and "G", this specifies the maximum number of digits to show,
-including thoe prior to the decimal point and those after it; for
+including those prior to the decimal point and those after it; for
example:
# These examples are subject to system-specific variation.
=item size
For numeric conversions, you can specify the size to interpret the
-number as using C<l>, C<h>, C<V>, C<q>, C<L>, or C<ll>. For integer
+number as using C<l>, C<h>, C<V>, C<q>, C<L>, or C<ll>. For integer
conversions (C<d u o x X b i D U O>), numbers are usually assumed to be
whatever the default integer size is on your platform (usually 32 or 64
bits), but you can override this to use instead one of the standard C types,
as supported by the compiler used to build Perl:
- l interpret integer as C type "long" or "unsigned long"
+ hh interpret integer as C type "char" or "unsigned char"
+ on Perl 5.14 or later
h interpret integer as C type "short" or "unsigned short"
- q, L or ll interpret integer as C type "long long", "unsigned long long".
- or "quads" (typically 64-bit integers)
+ j interpret integer as C type "intmax_t" on Perl 5.14
+ or later, and only with a C99 compiler (unportable)
+ l interpret integer as C type "long" or "unsigned long"
+ q, L, or ll interpret integer as C type "long long", "unsigned long long",
+ or "quad" (typically 64-bit integers)
+ t interpret integer as C type "ptrdiff_t" on Perl 5.14 or later
+ z interpret integer as C type "size_t" on Perl 5.14 or later
+
+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:
-The last will raise an exception if Perl does not understand "quads" in your
-installation. (This requires either that the platform natively support quads,
-or that Perl were specifically compiled to support quads.) You can find out
-whether your Perl supports quads via L<Config>:
+ use warnings FATAL => "printf";
+
+If you would like to know about a version dependency before you
+start running the program, put something like this at its top:
+
+ use 5.014; # for hh/j/t/z/ printf modifiers
+
+You can find out whether your Perl supports quads via L<Config>:
use Config;
if ($Config{use64bitint} eq "define" || $Config{longsize} >= 8) {
For floating-point conversions (C<e f g E F G>), numbers are usually assumed
to be the default floating-point size on your platform (double or long double),
but you can force "long double" with C<q>, C<L>, or C<ll> if your
-platform supports them. You can find out whether your Perl supports long
+platform supports them. You can find out whether your Perl supports long
doubles via L<Config>:
use Config;
=item order of arguments
Normally, sprintf() takes the next unused argument as the value to
-format for each format specification. If the format specification
+format for each format specification. If the format specification
uses C<*> to require additional arguments, these are consumed from
the argument list in the order they appear in the format
specification I<before> the value to format. Where an argument is
=back
-If C<use locale> is in effect and POSIX::setlocale() has been called,
+If C<use locale> (including C<use locale 'not_characters'>) is in effect
+and POSIX::setlocale() has been called,
the character used for the decimal separator in formatted floating-point
numbers is affected by the LC_NUMERIC locale. See L<perllocale>
and L<POSIX>.
=item sqrt
+=for Pod::Functions square root function
+
Return the positive square root of EXPR. If EXPR is omitted, uses
C<$_>. Works only for non-negative operands unless you've
loaded the C<Math::Complex> module.
=item srand
+=for Pod::Functions seed the random number generator
+
Sets and returns the random number seed for the C<rand> 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 (semi-)randomly chooses a seed. In either case, starting with
-Perl 5.14, it returns the seed.
+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
+(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, this was not true
But there are a few situations in recent Perls 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 other case is where you need a cryptographically-strong
-starting point rather than the generally acceptable default, which is based on
-time of day, process ID, and memory allocation, or the F</dev/urandom> device
-if available. And still another case is that you may want to call C<srand()>
+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).
programs supply their own seed value (often C<time ^ $$> or C<time ^
($$ + ($$ << 15))>), but that isn't necessary any more.
-For cryptographic purposes, however, you need something much more random
-than the default seed. Checksumming the compressed output of one or more
-rapidly changing operating system status programs is the usual method. For
-example:
-
- srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip -f`);
-
-If you're particularly concerned with this, search the CPAN for
-random number generator modules instead of rolling out your own.
-
Frequently called programs (like CGI scripts) that simply use
time ^ $$
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 exact results.
+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
+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,
+including: L<Data::Entropy>, L<Crypt::Random>, L<Math::Random::Secure>,
+and L<Math::TrulyRandom>.
=item stat FILEHANDLE
X<stat> X<file, status> X<ctime>
=item stat
+=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<$_>. Returns the empty list if C<stat> fails. Typically
+omitted, it stats C<$_> (not C<_>!). Returns the empty list if C<stat> fails. Typically
used as follows:
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
(The epoch was at 00:00 January 1, 1970 GMT.)
-(*) Not all fields are supported on all filesystem types. Notably, the
+(*) Not all fields are supported on all filesystem types. Notably, 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.
+"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
S_IRWXO S_IROTH S_IWOTH S_IXOTH
# Setuid/Setgid/Stickiness/SaveText.
- # Note that the exact meaning of these is system dependent.
+ # Note that the exact meaning of these is system-dependent.
S_ISUID S_ISGID S_ISVTX S_ISTXT
- # File types. Not necessarily all are available on your system.
+ # File types. Not all are necessarily available on
+ # your system.
- S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT
+ S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR
+ S_IFIFO S_IFSOCK S_IFWHT S_ENFMT
- # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR.
+ # The following are compatibility aliases for S_IRUSR,
+ # S_IWUSR, and S_IXUSR.
S_IREAD S_IWRITE S_IEXEC
and the C<S_IF*> functions are
- S_IMODE($mode) the part of $mode containing the permission bits
- and the setuid/setgid/sticky bits
+ S_IMODE($mode) the part of $mode containing the permission
+ bits and the setuid/setgid/sticky bits
- S_IFMT($mode) the part of $mode containing the file type
- which can be bit-anded with (for example) S_IFREG
- or with the following functions
+ S_IFMT($mode) the part of $mode containing the file type
+ which can be bit-anded with (for example)
+ S_IFREG or with the following functions
# The operators -f, -d, -l, -b, -c, -p, and -S.
about the C<S_*> constants. To get status info for a symbolic link
instead of the target file behind the link, use the C<lstat> function.
+Portability issues: L<perlport/stat>.
+
=item state EXPR
X<state>
=item state TYPE EXPR : ATTRS
-C<state> declares a lexically scoped variable, just like C<my> does.
+=for Pod::Functions +state declare and assign a persistent lexical variable
+
+C<state> declares a lexically scoped variable, just like C<my>.
However, those variables will never be reinitialized, contrary to
lexical variables that are reinitialized each time their enclosing block
is entered.
+See L<perlsub/"Persistent Private Variables"> for details.
C<state> variables are enabled only when the C<use feature "state"> pragma
-is in effect. See L<feature>.
+is in effect, unless the keyword is written as C<CORE::state>.
+See also L<feature>.
=item study SCALAR
X<study>
=item study
+=for Pod::Functions optimize input data for repeated searches
+
Takes extra time to study SCALAR (C<$_> 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 on, and on the distribution of character
+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 runs faster. Those loops
+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. You may have only
-one C<study> active at a time: if you study a different scalar the first
-is "unstudied". (The way C<study> works is this: a linked list of every
+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
=item sub NAME (PROTO) : ATTRS BLOCK
-This is subroutine definition, not a real function I<per se>.
-Without a BLOCK it's just a forward declaration. Without a NAME,
-it's an anonymous function declaration, and does actually return
-a value: the CODE ref of the closure you just created.
+=for Pod::Functions declare a subroutine, possibly anonymously
+
+This is subroutine definition, not a real function I<per se>. Without a
+BLOCK it's just a forward declaration. Without a NAME, it's an anonymous
+function declaration, so does return a value: the CODE ref of the closure
+just created.
See L<perlsub> and L<perlref> for details about subroutines and
-references
, and L<attributes> and L<Attribute::Handlers> for more
+references
; see L<attributes> and L<Attribute::Handlers> for more
information about attributes.
+=item __SUB__
+X<__SUB__>
+
+=for Pod::Functions +current_sub the current subroutine, or C<undef> if not in a subroutine
+
+A special token that returns the a reference to the current subroutine, or
+C<undef> outside of a subroutine.
+
+This token is only available under C<use v5.16> or the "current_sub"
+feature. See L<feature>.
+
=item substr EXPR,OFFSET,LENGTH,REPLACEMENT
X<substr> X<substring> X<mid> X<left> X<right>
=item substr EXPR,OFFSET
+=for Pod::Functions get or alter a portion of a string
+
Extracts a substring out of EXPR and returns it. First character is at
-offset C<0>, or whatever you've set C<$[> to (but don't do that).
-If OFFSET is negative (or more precisely, less than C<$[>), starts
-that far from the end of the string. If LENGTH is omitted, returns
-everything to the end of the string. If LENGTH is negative, leaves that
+offset zero. If OFFSET is negative, starts
+that far back from the end of the string. If LENGTH is omitted, returns
+everything through the end of the string. If LENGTH is negative, leaves that
many characters off the end of the string.
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 3-arg version of substr() acts as
+Note that the lvalue returned by the three-argument version of substr() acts as
a 'magic bullet'; each time it is assigned to, it remembers which part
of the original string is being modified; for example:
$_ = 'pq'; print $x,"\n"; # prints 5pq9
}
-Prior to Perl version 5.9.1, the result of using an lvalue multiple times was
+With negative offsets, it remembers its position from the end of the string
+when the target string is modified:
+
+ $x = '1234';
+ for (substr($x, -3, 2)) {
+ $_ = 'a'; print $x,"\n"; # prints 1a4, as above
+ $x = 'abcdefg';
+ print $_,"\n"; # prints f
+ }
+
+Prior to Perl version 5.10, the result of using an lvalue multiple times was
+unspecified. Prior to 5.16, the result with negative offsets was
unspecified.
=item symlink OLDFILE,NEWFILE
X<symlink> X<link> X<symbolic link> X<link, symbolic>
+=for Pod::Functions create a symbolic link to a file
+
Creates a new filename symbolically linked to the old filename.
Returns C<1> for success, C<0> otherwise. On systems that don't support
symbolic links, raises an exception. To check for that,
$symlink_exists = eval { symlink("",""); 1 };
+Portability issues: L<perlport/symlink>.
+
=item syscall NUMBER, LIST
X<syscall> X<system call>
+=for Pod::Functions execute an arbitrary system call
+
Calls the system call specified as the first element of the list,
passing the remaining elements as arguments to the system call. If
unimplemented, raises an exception. The arguments are interpreted
Syscall returns whatever value returned by the system call it calls.
If the system call fails, C<syscall> returns C<-1> and sets C<$!> (errno).
-Note that some system calls can legitimately return C<-1>. The proper
-way to handle such calls is to assign C<$!=0;> before the call and
-check the value of C<$!> if syscall returns C<-1>.
+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>.
There's a problem with C<syscall(&SYS_pipe)>: it returns the file
-number of the read end of the pipe it creates. There is no way
+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.
+Portability issues: L<perlport/syscall>.
+
=item sysopen FILEHANDLE,FILENAME,MODE
X<sysopen>
=item sysopen FILEHANDLE,FILENAME,MODE,PERMS
-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 name of the real filehandle wanted. This function calls the
-underlying operating system's C<open> function with the parameters
-FILENAME, MODE, PERMS.
+=for Pod::Functions +5.002 open a file, pipe, or descriptor
+
+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
+parameters FILENAME, MODE, and PERMS.
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 C<open> to see which
-values and flag bits are available. You may combine several flags
+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
+which values and flag bits are available. You may combine several flags
using the C<|>-operator.
Some of the most common values are C<O_RDONLY> for opening the file in
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
+exceed a certain value, typically 255. If you need more file
descriptors than that, consider rebuilding Perl to use the C<sfio>
library, or perhaps using the POSIX::open() function.
See L<perlopentut> for a kinder, gentler explanation of opening files.
+Portability issues: L<perlport/sysopen>.
+
=item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
X<sysread>
=item sysread FILEHANDLE,SCALAR,LENGTH
+=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>,
=item sysseek FILEHANDLE,POSITION,WHENCE
X<sysseek> X<lseek>
-Sets FILEHANDLE's system position in bytes using
-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).
+=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
+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 this with reads (other
-than C<sysread>
, for example C<< <> >> or read()) C<print>, C<write>,
+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.
For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>,
=item system PROGRAM LIST
+=for Pod::Functions run a separate program
+
Does exactly the same thing as C<exec LIST>, except that a fork is
-done first, and the parent process waits for the child process to
+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,
or if LIST is an array with more than one value, starts the program
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
+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 $! for the reason).
See L<perlop/"`STRING`"> and L</exec> for details.
Since C<system> does a C<fork> and C<wait> it may affect a C<SIGCHLD>
-handler. See L<perlipc> for details.
+handler. See L<perlipc> for details.
+
+Portability issues: L<perlport/system>.
=item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
X<syswrite>
=item syswrite FILEHANDLE,SCALAR
+=for Pod::Functions fixed-length unbuffered output to a filehandle
+
Attempts to write LENGTH bytes of data from variable SCALAR to the
specified FILEHANDLE, using write(2). If LENGTH is
not specified, writes whole SCALAR. It bypasses buffered IO, so
mixing this with reads (other than C<sysread())>, C<print>, C<write>,
C<seek>, C<tell>, or C<eof> may cause confusion because the perlio and
-stdio layers usually buffers data. Returns the number of bytes
+stdio layers usually buffer data. Returns the number of bytes
actually written, or C<undef> if there was an error (in this case the
errno variable C<$!> is also set). If the LENGTH is greater than the
data available in the SCALAR after the OFFSET, only as much data as is
that many characters counting backwards from the end of the string.
If SCALAR is of length zero, you can only use an OFFSET of 0.
-B<Warning>: If the filehandle is marked C<:utf8>, Unicode characters
+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 (UTF-8 encoded Unicode) characters.
+return value of syswrite() 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>.
=item tell FILEHANDLE
=item tell
+=for Pod::Functions get current seekpointer on a filehandle
+
Returns the current position I<in bytes> for FILEHANDLE, or -1 on
error. FILEHANDLE may be an expression whose value gives the name of
the actual filehandle. If FILEHANDLE is omitted, assumes the file
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().
+that has been manipulated by sysread(), syswrite(), or sysseek().
Those functions ignore the buffering, while tell() 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
=item tie VARIABLE,CLASSNAME,LIST
X<tie>
+=for Pod::Functions +5.002 bind a variable to an object class
+
This function binds a variable to a package class that will provide the
implementation for the variable. VARIABLE is the name of the variable
to be enchanted. CLASSNAME is the name of a class implementing objects
=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
to a package.) Returns the undefined value if VARIABLE isn't tied to a
=item time
X<time> X<epoch>
+=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;
+C<localtime>. 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,
-you may use either the L<Time::HiRes> module (from CPAN, and starting from
-Perl 5.8 part of the standard distribution), or if you have
-gettimeofday(2), you may be able to use the C<syscall> interface of Perl.
-See L<perlfaq8> for details.
+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.
For date and time processing look at the many related modules on CPAN.
For a comprehensive date and time representation look at the
=item times
X<times>
-Returns a four-element list giving the user and system times, in
-seconds, for this process and the children of this process.
+=for Pod::Functions return elapsed time for self and child processes
+
+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;
Children's times are only included for terminated children.
+Portability issues: L<perlport/times>.
+
=item tr///
+=for Pod::Functions transliterate a string
+
The transliteration operator. Same as C<y///>. See
L<perlop/"Quote and Quote-like Operators">.
=item truncate EXPR,LENGTH
+=for Pod::Functions shorten a file
+
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, the undefined value
-otherwise.
+on your system. Returns true if successful, C<undef> 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.
+Portability issues: L<perlport/truncate>.
+
=item uc EXPR
X<uc> X<uppercase> X<toupper>
=item uc
+=for Pod::Functions return upper-case version of a string
+
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
=item ucfirst
+=for Pod::Functions return a string with just the next letter in upper case
+
Returns the value of EXPR with the first character in uppercase
(titlecase in Unicode). This is the internal function implementing
the C<\u> escape in double-quoted strings.
=item umask
+=for Pod::Functions set file creation mode mask
+
Sets the umask for the process to EXPR and returns the previous value.
If EXPR is omitted, merely returns the current umask.
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
+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> (C<0666 &~
-027> is C<0640>).
+C<sysopen> 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
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.
+Portability issues: L<perlport/umask>.
+
=item undef EXPR
X<undef> X<undefine>
=item undef
+=for Pod::Functions remove a variable or function definition
+
Undefines the value of EXPR, which must be an lvalue. Use only on a
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
+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
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
=item unlink
-Deletes a list of files. On success, it returns the number of files
-it successfully deleted. On failure, it returns false and sets C<$!>
+=for Pod::Functions remove one link to a file
+
+Deletes a list of files. On success, it returns the number of files
+it successfully deleted. On failure, it returns false and sets C<$!>
(errno):
my $unlinked = unlink 'a', 'b', 'c';
}
Note: C<unlink> will not attempt to delete directories unless you are
-superuser and the B<-U> flag is supplied to Perl. Even if these
+superuser and the B<-U> flag is supplied to Perl. Even if these
conditions are met, be warned that unlinking a directory can inflict
damage on your filesystem. Finally, using C<unlink> on directories is
not supported on many operating systems. Use C<rmdir> instead.
=item unpack TEMPLATE
+=for Pod::Functions convert binary structure into normal perl variables
+
C<unpack> does the reverse of C<pack>: it takes a string
and expands it out into a list of values.
(In scalar context, it returns merely the first value produced.)
you want a <number>-bit checksum of the items instead of the items
themselves. Default is a 16-bit checksum. Checksum is calculated by
summing numeric values of expanded values (for string fields the sum of
-C<ord($char)> is taken, for bit fields the sum of zeroes and ones).
+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:
See L</pack> for more examples and notes.
-=item untie VARIABLE
-X<untie>
+=item unshift ARRAY,LIST
+X<unshift>
-Breaks the binding between a variable and a package. (See C<tie>.)
-Has no effect if the variable is not tied.
+=item unshift EXPR,LIST
-=item unshift ARRAY (or ARRAYREF),LIST
-X<unshift>
+=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>,
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.
+array and returns the new number of elements in the array.
unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;
prepended elements stay in the same order. Use C<reverse> to do the
reverse.
-If given a reference to an array, the argument will be dereferenced
-automatically.
+Starting with Perl 5.14, C<unshift> can take a scalar EXPR, which must hold
+a reference to an unblessed array. The argument will be dereferenced
+automatically. This aspect of C<unshift> is considered highly
+experimental. The exact behaviour may change in a future version of Perl.
+
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
+=item untie VARIABLE
+X<untie>
+
+=for Pod::Functions break a tie binding to a variable
+
+Breaks the binding between a variable and a package.
+(See L<tie|/tie VARIABLE,CLASSNAME,LIST>.)
+Has no effect if the variable is not tied.
=item use Module VERSION LIST
X<use> X<module> X<import>
=item use VERSION
+=for Pod::Functions load in a module at compile time and import its namespace
+
Imports some semantics into the current package from the named module,
generally by aliasing certain subroutine or variable names into your
package. It is exactly equivalent to
BEGIN { require Module; Module->import( LIST ); }
except that Module I<must> be a bareword.
+The importation can be made conditional; see L<if>.
In the peculiar C<use VERSION> form, VERSION may be either a positive
decimal fraction such as 5.006, which will be compared to C<$]>, or a v-string
C<use>ing library modules that won't work with older versions of Perl.
(We try not to do this more than we have to.)
-Also, if the specified Perl version is greater than or equal to 5.9.5,
-C<use VERSION> will also load the C<feature> pragma and enable all
-features available in the requested version. See L<feature>.
+C<use VERSION> also enables all features available in the requested
+version as defined by the C<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
-5.11.0, strictures are enabled lexically as with C<use strict> (except
-that the F<strict.pm> file is not actually loaded).
+5.11.0, strictures are enabled lexically as
+with C<use strict>. Any explicit use of
+C<use strict> or C<no strict> overrides C<use VERSION>, even if it comes
+before it. In both cases, the F<feature.pm> and F<strict.pm> files are
+not actually loaded.
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
use if $] < 5.008, "utf8";
use if WANT_WARNINGS, warnings => qw(all);
-There's a corresponding C<no> command that unimports meanings imported
+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,
or no unimport method being found.
no warnings;
Care should be taken when using the C<no VERSION> form of C<no>. It is
-I<only> meant to be used to assert that the running perl is of a earlier
+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>.
=item utime LIST
X<utime>
+=for Pod::Functions set a file's last access and modify times
+
Changes the access and modification times on each file of a list of
-files. The first two elements of the list must be the NUMERICAL access
+files. The first two elements of the list must be the NUMERIC access
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
Since Perl 5.7.2, 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
-argument. On most systems, this will set the file's access and
+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:
an exception. Filehandles must be passed as globs or glob references to be
recognized; barewords are considered filenames.
-=item values HASH (or HASHREF)
+Portability issues: L<perlport/utime>.
+
+=item values HASH
X<values>
-=item values ARRAY (or ARRAYREF)
+=item values ARRAY
-Returns a list consisting of all the values of the named hash, or the values
-of an array. (In a scalar context, returns the number of values.)
+=item values EXPR
-The values are returned in an apparently random order. The actual
-random order is subject to change in future versions of Perl, but it
-is guaranteed to be the same order as either the C<keys> or C<each>
-function would produce on the same (unmodified) hash. Since Perl
-5.8.1 the ordering is different even between different runs of Perl
-for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
+=for Pod::Functions return a list of the values in a hash
-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>.
-We recommend that you use void context C<keys @array> for this, but reasoned
-that it taking C<values @array> out would require more documentation than
-leaving it in.)
+In list context, returns a list consisting of all the values of the named
+hash. In Perl 5.12 or later only, will also return a list of the values of
+an array; prior to that release, attempting to use an array argument will
+produce a syntax error. In scalar context, returns the number of values.
+When called on a hash, the values are returned in an apparently random
+order. The actual random order is subject to change in future versions of
+Perl, but it is guaranteed to be the same order as either the C<keys> or
+C<each> function would produce on the same (unmodified) hash. Since Perl
+5.8.1 the ordering is different even between different runs of Perl for
+security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
+
+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>.
+(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.)
Note that the values are not copied, which means modifying them will
modify the contents of the hash:
for (values %hash) { s/foo/bar/g } # modifies %hash values
for (@hash{keys %hash}) { s/foo/bar/g } # same
-When given a reference to a hash or array, the argument will be
-dereferenced automatically.
+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 $obj->get_arrayref) { ... }
-If the reference is a blessed object that overrides either C<%{}> or
-C<@{}>, the override will be used instead of dereferencing the underlying
-variable type. If both overrides are provided, C<%{}> will be the default.
-If this is not desired, you must dereference the argument yourself.
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.012; # so keys/values/each work on arrays
+ use 5.014; # so keys/values/each work on scalars (experimental)
See also C<keys>, C<each>, and C<sort>.
=item vec EXPR,OFFSET,BITS
X<vec> X<bit> X<bit vector>
+=for Pod::Functions test or set particular bits in a string
+
Treats the string in EXPR as a bit vector made up of elements of
-width BITS, and returns the value of the element specified by OFFSET
+width BITS and returns the value of the element specified by OFFSET
as an unsigned integer. BITS therefore specifies the number of bits
that are reserved for each element in the bit vector. This must
be a power of two from 1 to 32 (or 64, if your platform supports
=item wait
X<wait>
+=for Pod::Functions wait for any child process to die
+
Behaves like wait(2) on your system: it waits for a child
process to terminate and returns the pid of the deceased process, or
C<-1> if there are no child processes. The status is returned in C<$?>
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.
+child created by qx() or system(). See L<perlipc> for details.
+
+Portability issues: L<perlport/wait>.
=item waitpid PID,FLAGS
X<waitpid>
+=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.
processes are being automatically reaped. See L<perlipc> for details,
and for other examples.
+Portability issues: L<perlport/waitpid>.
+
=item wantarray
X<wantarray> X<context>
+=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
looking for a scalar. Returns the undefined value if the context is
=item warn LIST
X<warn> X<warning> X<STDERR>
+=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.
# run-time warnings enabled after here
warn "\$foo is alive and $foo!"; # does show up
-See L<perlvar> for details on setting C<%SIG> entries, and for more
+See L<perlvar> for details on setting C<%SIG> entries and for more
examples. See the Carp module for other kinds of warnings using its
carp() and cluck() functions.
=item write
+=for Pod::Functions print a picture record
+
Writes a formatted record (possibly multi-line) to the specified FILEHANDLE,
using the format associated with that file. By default the format for
a file is the one having the same name as the filehandle, but the
format for the current output channel (see the C<select> function) may be set
explicitly by assigning the name of the format to the C<$~> variable.
-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, a special top-of-page format
-is used to format the new page header, and then the record is written.
-By default the top-of-page format is the name of the filehandle with
-"_TOP" appended, but it may be dynamically set to the format of your
-choice by assigning the name to the C<$^> variable while the filehandle is
-selected. The number of lines remaining on the current page is in
-variable C<$->, which can be set to C<0> to force a new page.
+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, 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. 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.
If FILEHANDLE is unspecified, output goes to the current default output
channel, which starts out as STDOUT but may be changed by the
=item y///
+=for Pod::Functions transliterate a string
+
The transliteration operator. Same as C<tr///>. See
L<perlop/"Quote and Quote-like Operators">.
=back
+
+=head2 Non-function Keywords by Cross-reference
+
+=head3 perldata
+
+=over
+
+=item __DATA__
+
+=item __END__
+
+These keywords are documented in L<perldata/"Special Literals">.
+
+=back
+
+=head3 perlmod
+
+=over
+
+=item BEGIN
+
+=item CHECK
+
+=item END
+
+=item INIT
+
+=item UNITCHECK
+
+These compile phase keywords are documented in L<perlmod/"BEGIN, UNITCHECK, CHECK, INIT and END">.
+
+=back
+
+=head3 perlobj
+
+=over
+
+=item DESTROY
+
+This method keyword is documented in L<perlobj/"Destructors">.
+
+=back
+
+=head3 perlop
+
+=over
+
+=item and
+
+=item cmp
+
+=item eq
+
+=item ge
+
+=item gt
+
+=item if
+
+=item le
+
+=item lt
+
+=item ne
+
+=item not
+
+=item or
+
+=item x
+
+=item xor
+
+These operators are documented in L<perlop>.
+
+=back
+
+=head3 perlsub
+
+=over
+
+=item AUTOLOAD
+
+This keyword is documented in L<perlsub/"Autoloading">.
+
+=back
+
+=head3 perlsyn
+
+=over
+
+=item else
+
+=item elseif
+
+=item elsif
+
+=item for
+
+=item foreach
+
+=item unless
+
+=item until
+
+=item while
+
+These flow-control keywords are documented in L<perlsyn/"Compound Statements">.
+
+=back
+
+=over
+
+=item default
+
+=item given
+
+=item when
+
+These flow-control keywords related to the experimental switch feature are
+documented in L<perlsyn/"Switch Statements"> .
+
+=back
+
+=cut
https://perl5.git.perl.org / perl5.git / blobdiff