=head1 NAME
+X<function>
perlfunc - Perl builtin functions
last value in the list. Some operators return a count of successful
operations. In general, they do what you want, unless you want
consistency.
+X<context>
A named array in scalar context is quite different from what would at
first glance appear to be a list in scalar context. You can't get a list
variable on failure. Other functions do not, except accidentally.
=head2 Perl Functions by Category
+X<function>
Here are Perl's functions (including things that look like
functions, like some keywords and named operators)
=over 4
=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/STRING/>, C<qq/STRING/>, C<reverse>,
+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///>
=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//>
=item Numeric functions
+X<numeric> X<number> X<trigonometric> X<trigonometry>
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>
C<pop>, C<push>, C<shift>, C<splice>, C<unshift>
=item Functions for list data
+X<list>
-C<grep>, C<join>, C<map>, C<qw/STRING/>, C<reverse>, C<sort>, C<unpack>
+C<grep>, C<join>, C<map>, C<qw//>, C<reverse>, C<sort>, C<unpack>
=item Functions for real %HASHes
+X<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>
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<seek>, C<seekdir>, C<select>, C<syscall>,
+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<pack>, C<read>, C<syscall>, C<sysread>, 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>
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<umask>, C<unlink>, C<utime>
=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>
+=item Keywords related to switch
+
+C<break>, C<continue>, C<given>, C<when>, C<default>
+
+(These are only available if you enable the "switch" feature.
+See L<feature> and L<perlsyn/"Switch statements">.)
+
=item Keywords related to scoping
-C<caller>, C<import>, C<local>, C<my>, C<our>, C<package>, C<use>
+C<caller>, C<import>, C<local>, C<my>, C<our>, C<state>, C<package>,
+C<use>
+
+(C<state> is only available if the "state" feature is enabled. See
+L<feature>.)
=item Miscellaneous functions
-C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<our>, C<reset>,
-C<scalar>, C<undef>, C<wantarray>
+C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<our>,
+C<reset>, C<scalar>, C<state>, C<undef>, C<wantarray>
=item Functions for processes and process groups
+X<process> X<pid> X<process id>
C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>,
-C<pipe>, C<qx/STRING/>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>,
+C<pipe>, C<qx//>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>,
C<times>, C<wait>, C<waitpid>
=item Keywords related to perl modules
+X<module>
C<do>, C<import>, C<no>, C<package>, C<require>, C<use>
=item Keywords related to classes and object-orientedness
+X<object> X<class> X<package>
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>
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>
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>
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>
C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>,
C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
C<setnetent>, C<setprotoent>, C<setservent>
=item Time-related functions
+X<time> X<date>
C<gmtime>, C<localtime>, C<time>, C<times>
=item Functions new in perl5
+X<perl5>
-C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>,
-C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<our>, C<prototype>,
-C<qx>, C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>,
-C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use>
+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<sub> was a keyword in perl4, but in perl5 it is an
operator, which can be used in expressions.
=back
=head2 Portability
+X<portability> X<Unix> X<portable>
Perl was born in Unix and can therefore access all common Unix
system calls. In non-Unix environments, the functionality of some
=over 8
=item -X FILEHANDLE
+X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p>
+X<-S>X<-b>X<-c>X<-t>X<-u>X<-g>X<-k>X<-T>X<-B>X<-M>X<-A>X<-C>
=item -X EXPR
+=item -X DIRHANDLE
+
=item -X
A file test, where X is one of the letters listed below. This unary
-operator takes one argument, either a filename or a filehandle, and
-tests the associated file to see if something is true about it. If the
+operator takes one argument, either a filename, a filehandle, or a dirhandle,
+and tests the associated file to see if something is true about it. If the
argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN.
Unless otherwise documented, it returns C<1> for true and C<''> for false, or
the undefined value if the file doesn't exist. Despite the funny
-names, precedence is the same as any other named unary operator, and
-the argument may be parenthesized like any other unary operator. The
+names, precedence is the same as any other named unary operator. The
operator may be any of:
-X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p>
-X<-S>X<-b>X<-c>X<-t>X<-u>X<-g>X<-k>X<-T>X<-B>X<-M>X<-A>X<-C>
-r File is readable by effective uid/gid.
-w File is writable by effective uid/gid.
operator, no special magic will happen.)
=item abs VALUE
+X<abs> X<absolute>
=item abs
If VALUE is omitted, uses C<$_>.
=item accept NEWSOCKET,GENERICSOCKET
+X<accept>
Accepts an incoming socket connect, just as the accept(2) system call
does. Returns the packed address if it succeeded, false otherwise.
value of $^F. See L<perlvar/$^F>.
=item alarm SECONDS
+X<alarm>
+X<SIGALRM>
+X<timer>
=item alarm
For more information see L<perlipc>.
=item atan2 Y,X
+X<atan2> X<arctangent> X<tan> X<tangent>
Returns the arctangent of Y/X in the range -PI to PI.
sub tan { sin($_[0]) / cos($_[0]) }
+Note that atan2(0, 0) is not well-defined.
+
=item bind SOCKET,NAME
+X<bind>
Binds a network address to a socket, just as the bind system call
does. Returns true if it succeeded, false otherwise. NAME should be a
L<perlipc/"Sockets: Client/Server Communication">.
=item binmode FILEHANDLE, LAYER
+X<binmode> X<binary> X<text> X<DOS> X<Windows>
=item binmode FILEHANDLE
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) or elsewhere, C<:raw> is I<not> the simply inverse of C<:crlf>
--- other layers which would affect binary nature of the stream are
+Camel) or elsewhere, C<:raw> is I<not> simply the inverse of C<:crlf>
+-- other layers which would affect the binary nature of the stream are
I<also> disabled. See L<PerlIO>, L<perlrun> and the discussion about the
PERLIO environment variable.
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>.
+To mark FILEHANDLE as UTF-8, use C<:utf8> or C<:encoding(utf8)>.
+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>.
In general, binmode() should be called after open() but before any I/O
is done on the filehandle. Calling binmode() will normally flush any
line-termination sequences.
=item bless REF,CLASSNAME
+X<bless>
=item bless REF
See L<perlmod/"Perl Modules">.
+=item break
+
+Break out of a C<given()> block.
+
+This keyword is enabled by the "switch" feature: see L<feature>
+for more information.
+
=item caller EXPR
+X<caller> X<call stack> X<stack> X<stack trace>
=item caller
we're in a subroutine or C<eval> or C<require>, and the undefined value
otherwise. In list context, returns
+ # 0 1 2
($package, $filename, $line) = caller;
With EXPR, it returns some extra information that the debugger uses to
print a stack trace. The value of EXPR indicates how many call frames
to go back before the current one.
+ # 0 1 2 3 4
($package, $filename, $line, $subroutine, $hasargs,
- $wantarray, $evaltext, $is_require, $hints, $bitmask) = caller($i);
+
+ # 5 6 7 8 9 10
+ $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash)
+ = caller($i);
Here $subroutine may be C<(eval)> if the frame is not a subroutine
call, but an C<eval>. In such a case additional elements $evaltext and
compiled with. The C<$hints> and C<$bitmask> values are subject to change
between versions of Perl, and are not meant for external use.
+C<$hinthash> is a reference to a hash containing the value of C<%^H> when the
+caller was compiled, or C<undef> if C<%^H> was empty. Do not modify the values
+of this hash, as they are the actual values stored in the optree.
+
Furthermore, when called from within the DB package, caller returns more
detailed information: it sets the list variable C<@DB::args> to be the
arguments with which the subroutine was invoked.
previous time C<caller> was called.
=item chdir EXPR
+X<chdir>
+X<cd>
+X<directory, change>
=item chdir FILEHANDLE
passing handles produces a fatal error at run time.
=item chmod LIST
+X<chmod> X<permission> X<mode>
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
On systems that support fchmod, you might pass file handles among the
files. On systems that don't support fchmod, passing file handles
-produces a fatal error at run time.
+produces a fatal error at run time. The file handles must be passed
+as globs or references to be recognized. Barewords are considered
+file names.
open(my $fh, "<", "foo");
my $perm = (stat $fh)[2] & 07777;
# This is identical to the chmod 0755 of the above example.
=item chomp VARIABLE
+X<chomp> X<INPUT_RECORD_SEPARATOR> X<$/> X<newline> X<eol>
=item chomp( LIST )
If you chomp a list, each element is chomped, and the total number of
characters removed is returned.
-If the C<encoding> pragma is in scope then the lengths returned are
-calculated from the length of C<$/> in Unicode characters, which is not
-always the same as the length of C<$/> in the native encoding.
-
Note that parentheses are necessary when you're chomping anything
that is not a simple variable. This is because C<chomp $cwd = `pwd`;>
is interpreted as C<(chomp $cwd) = `pwd`;>, rather than as
as C<chomp($a, $b)>.
=item chop VARIABLE
+X<chop>
=item chop( LIST )
See also L</chomp>.
=item chown LIST
+X<chown> X<owner> X<user> X<group>
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
On systems that support fchown, you might pass file handles among the
files. On systems that don't support fchown, passing file handles
-produces a fatal error at run time.
+produces a fatal error at run time. The file handles must be passed
+as globs or references to be recognized. Barewords are considered
+file names.
Here's an example that looks up nonnumeric uids in the passwd file:
$can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);
=item chr NUMBER
+X<chr> X<character> X<ASCII> X<Unicode>
=item chr
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
-chr(0x263a) is a Unicode smiley face. Note that characters from 128
-to 255 (inclusive) are by default not encoded in UTF-8 Unicode for
-backward compatibility reasons (but see L<encoding>).
+chr(0x263a) is a Unicode smiley face.
Negative values give the Unicode replacement character (chr(0xfffd)),
-except under the L</bytes> pragma, where low eight bits of the value
+except under the L<bytes> pragma, where low eight bits of the value
(truncated to an integer) are used.
If NUMBER is omitted, uses C<$_>.
For the reverse, use L</ord>.
-Note that under the C<bytes> pragma the NUMBER is masked to
-the low eight bits.
+Note that characters from 128 to 255 (inclusive) are by default
+internally not encoded as UTF-8 for backward compatibility reasons.
-See L<perlunicode> and L<encoding> for more about Unicode.
+See L<perlunicode> for more about Unicode.
=item chroot FILENAME
+X<chroot> X<root>
=item chroot
omitted, does a C<chroot> to C<$_>.
=item close FILEHANDLE
+X<close>
=item close
-Closes the file or pipe associated with the file handle, returning
-true only if IO buffers are successfully flushed and closes the system
-file descriptor. Closes the currently selected filehandle if the
-argument is omitted.
+Closes the file or pipe associated with the file handle, 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
+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> will close it for you. (See
filehandle, usually the real filehandle name.
=item closedir DIRHANDLE
+X<closedir>
Closes a directory opened by C<opendir> and returns the success of that
system call.
=item connect SOCKET,NAME
+X<connect>
Attempts to connect to a remote socket, just as the connect system call
does. Returns true if it succeeded, false otherwise. NAME should be a
L<perlipc/"Sockets: Client/Server Communication">.
=item continue BLOCK
+X<continue>
+
+=item continue
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
empty one, logically enough. In that case, C<next> goes directly back
to check the condition at the top of the loop.
+If the "switch" feature is enabled, C<continue> is also a
+function that will break out of the current C<when> or C<default>
+block, and fall through to the next case. See L<feature> and
+L<perlsyn/"Switch statements"> for more information.
+
+
=item cos EXPR
+X<cos> X<cosine> X<acos> X<arccosine>
=item cos
sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }
=item crypt PLAINTEXT,SALT
+X<crypt> X<digest> X<hash> X<salt> X<plaintext> X<password>
+X<decrypt> X<cryptography> X<passwd> X<encrypt>
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
C<Wide character in crypt>.
=item dbmclose HASH
+X<dbmclose>
[This function has been largely superseded by the C<untie> function.]
Breaks the binding between a DBM file and a hash.
=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.]
or die "Can't open netscape history file: $!";
=item defined EXPR
+X<defined> X<undef> X<undefined>
=item defined
See also L</undef>, L</exists>, L</ref>.
=item delete EXPR
+X<delete>
Given an expression that specifies a hash element, array element, hash slice,
or array slice, deletes the specified element(s) from the hash or array.
delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];
=item die LIST
+X<die> X<throw> X<exception> X<raise> X<$@> X<abort>
Outside an C<eval>, prints the value of LIST to C<STDERR> and
exits with the current value of C<$!> (errno). If C<$!> is C<0>,
a more elaborate exception handling implementation using objects that
maintain arbitrary state about the nature of the exception. Such a scheme
is sometimes preferable to matching particular string values of $@ using
-regular expressions. Here's an example:
+regular expressions. Because $@ is a global variable, and eval() may be
+used within object implementations, care must be taken that analyzing the
+error object doesn't replace the reference in the global variable. The
+easiest solution is to make a local copy of the reference before doing
+other manipulations. Here's an example:
use Scalar::Util 'blessed';
eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
- if ($@) {
- if (blessed($@) && $@->isa("Some::Module::Exception")) {
+ if (my $ev_err = $@) {
+ if (blessed($ev_err) && $ev_err->isa("Some::Module::Exception")) {
# handle Some::Module::Exception
}
else {
behavior may be fixed in a future release.
=item do BLOCK
+X<do> X<block>
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
See L<perlsyn> for alternative strategies.
=item do SUBROUTINE(LIST)
+X<do>
This form of subroutine call is deprecated. See L<perlsub>.
=item do EXPR
+X<do>
Uses the value of EXPR as a filename and executes the contents of the
file as a Perl script.
}
=item dump LABEL
+X<dump> X<core> X<undump>
=item dump
be open any more when the program is reincarnated, with possible
resulting confusion on the part of Perl.
-This function is now largely obsolete, partly because it's very
-hard to convert a core file into an executable, and because the
-real compiler backends for generating portable bytecode and compilable
-C code have superseded it. That's why you should now invoke it as
-C<CORE::dump()>, if you don't want to be warned against a possible
+This function is now largely obsolete, mostly because it's very hard to
+convert a core file into an executable. That's why you should now invoke
+it as C<CORE::dump()>, if you don't want to be warned against a possible
typo.
-If you're looking to use L<dump> to speed up your program, consider
-generating bytecode or native C code as described in L<perlcc>. If
-you're just trying to accelerate a CGI script, consider using the
-C<mod_perl> extension to B<Apache>, or the CPAN module, CGI::Fast.
-You might also consider autoloading or selfloading, which at least
-make your program I<appear> to run faster.
-
=item each HASH
+X<each> X<hash, iterator>
When called in list context, returns a 2-element list consisting of the
key and value for the next element of a hash, so that you can iterate over
See also C<keys>, C<values> and C<sort>.
=item eof FILEHANDLE
+X<eof>
+X<end of file>
+X<end-of-file>
=item eof ()
there was an error.
=item eval EXPR
+X<eval> X<try> X<catch> X<evaluate> X<parse> X<execute>
+X<error, handling> X<exception, handling>
=item eval BLOCK
need to worry about this unless you are writing a Perl debugger.
=item exec LIST
+X<exec> X<execute>
=item exec PROGRAM LIST
any C<DESTROY> methods in your objects.
=item exists EXPR
+X<exists> X<autovivification>
Given an expression that specifies a hash element or array element,
returns true if the specified element in the hash or array has ever
exists &sub(); # Error
=item exit EXPR
+X<exit> X<terminate> X<abort>
=item exit
See L<perlmod> for details.
=item exp EXPR
+X<exp> X<exponential> X<antilog> X<antilogarithm> X<e>
=item exp
If EXPR is omitted, gives C<exp($_)>.
=item fcntl FILEHANDLE,FUNCTION,SCALAR
+X<fcntl>
Implements the fcntl(2) function. You'll probably have to say
or die "Can't set flags for the socket: $!\n";
=item fileno FILEHANDLE
+X<fileno>
Returns the file descriptor for a filehandle, or undefined if the
filehandle is not open. This is mainly useful for constructing
=item flock FILEHANDLE,OPERATION
+X<flock> X<lock> X<locking>
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
See also L<DB_File> for other flock() examples.
=item fork
+X<fork> X<child> X<parent>
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
You should reopen those to F</dev/null> if it's any issue.
=item format
+X<format>
Declare a picture format for use by the C<write> function. For
example:
See L<perlform> for many details and examples.
=item formline PICTURE,LIST
+X<formline>
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
C<formline> always returns true. See L<perlform> for other examples.
=item getc FILEHANDLE
+X<getc> X<getchar> X<character> X<file, read>
=item getc
L<perlmodlib/CPAN>.
=item getlogin
+X<getlogin> X<login>
This implements the C library function of the same name, which on most
systems returns the current login from F</etc/utmp>, if any. If null,
secure as C<getpwuid>.
=item getpeername SOCKET
+X<getpeername> X<peer>
Returns the packed sockaddr address of other end of the SOCKET connection.
$herstraddr = inet_ntoa($iaddr);
=item getpgrp PID
+X<getpgrp> X<group>
Returns the current process group for the specified PID. Use
a PID of C<0> to get the current process group for the
does not accept a PID argument, so only C<PID==0> is truly portable.
=item getppid
+X<getppid> X<parent> X<pid>
Returns the process id of the parent process.
C<Linux::Pid>.
=item getpriority WHICH,WHO
+X<getpriority> X<priority> X<nice>
Returns the current priority for a process, a process group, or a user.
(See L<getpriority(2)>.) Will raise a fatal exception if used on a
machine that doesn't implement getpriority(2).
=item getpwnam NAME
+X<getpwnam> X<getgrnam> X<gethostbyname> X<getnetbyname> X<getprotobyname>
+X<getpwuid> X<getgrgid> X<getservbyname> X<gethostbyaddr> X<getnetbyaddr>
+X<getprotobynumber> X<getservbyport> X<getpwent> X<getgrent> X<gethostent>
+X<getnetent> X<getprotoent> X<getservent> X<setpwent> X<setgrent> X<sethostent>
+X<setnetent> X<setprotoent> X<setservent> X<endpwent> X<endgrent> X<endhostent>
+X<endnetent> X<endprotoent> X<endservent>
=item getgrnam NAME
a C<User::pwent> object.
=item getsockname SOCKET
+X<getsockname>
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
inet_ntoa($myaddr);
=item getsockopt SOCKET,LEVEL,OPTNAME
+X<getsockopt>
Queries the option named OPTNAME associated with SOCKET at a given LEVEL.
Options may exist at multiple protocol levels depending on the socket
=item glob EXPR
+X<glob> X<wildcard> X<filename, expansion> X<expand>
=item glob
C<File::Glob> extension. See L<File::Glob> for details.
=item gmtime EXPR
+X<gmtime> X<UTC> X<Greenwich>
=item gmtime
-Converts a time as returned by the time function to an 8-element list
-with the time localized for the standard Greenwich time zone.
-Typically used as follows:
-
- # 0 1 2 3 4 5 6 7
- ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) =
- gmtime(time);
-
-All list elements are numeric, and come straight out of the C `struct
-tm'. $sec, $min, and $hour are the seconds, minutes, and hours of the
-specified time. $mday is the day of the month, and $mon is the month
-itself, in the range C<0..11> with 0 indicating January and 11
-indicating December. $year is the number of years since 1900. That
-is, $year is C<123> in year 2023. $wday is the day of the week, with
-0 indicating Sunday and 3 indicating Wednesday. $yday is the day of
-the year, in the range C<0..364> (or C<0..365> in leap years.)
-
-Note that the $year element is I<not> simply the last two digits of
-the year. If you assume it is then you create non-Y2K-compliant
-programs--and you wouldn't want to do that, would you?
+Works just like L<localtime> but the returned values are
+localized for the standard Greenwich time zone.
-The proper way to get a complete 4-digit year is simply:
-
- $year += 1900;
-
-And to get the last two digits of the year (e.g., '01' in 2001) do:
-
- $year = sprintf("%02d", $year % 100);
-
-If EXPR is omitted, C<gmtime()> uses the current time (C<gmtime(time)>).
-
-In scalar context, C<gmtime()> returns the ctime(3) value:
-
- $now_string = gmtime; # e.g., "Thu Oct 13 04:54:34 1994"
-
-If you need local time instead of GMT use the L</localtime> builtin.
-See also the C<timegm> function provided by the C<Time::Local> module,
-and the strftime(3) and mktime(3) functions available via the L<POSIX> module.
-
-This scalar value is B<not> locale dependent (see L<perllocale>), but is
-instead a Perl builtin. To get somewhat similar but locale dependent date
-strings, see the example in L</localtime>.
+Note: when called in list context, $isdst, the last value
+returned by gmtime is always C<0>. There is no
+Daylight Saving Time in GMT.
See L<perlport/gmtime> for portability concerns.
=item goto LABEL
+X<goto> X<jump> X<jmp>
=item goto EXPR
reference.
=item grep BLOCK LIST
+X<grep>
=item grep EXPR,LIST
See also L</map> for a list composed of the results of the BLOCK or EXPR.
=item hex EXPR
+X<hex> X<hexadecimal>
=item hex
L</sprintf>, or L</unpack>.
=item import LIST
+X<import>
There is no builtin C<import> function. It is just an ordinary
method (subroutine) defined (or inherited) by modules that wish to export
for the package used. See also L</use>, L<perlmod>, and L<Exporter>.
=item index STR,SUBSTR,POSITION
+X<index> X<indexOf> X<InStr>
=item index STR,SUBSTR
the wildcard-like behavior of a full regular-expression pattern match.
It returns the position of the first occurrence of SUBSTR in STR at
or after POSITION. If POSITION is omitted, starts searching from the
-beginning of the string. The return value is based at C<0> (or whatever
+beginning of the string. POSITION before the beginning of the string
+or after its end is treated as if it were the beginning or the end,
+respectively. POSITION and the return value are based at C<0> (or whatever
you've set the C<$[> variable to--but don't do that). If the substring
is not found, C<index> returns one less than the base, ordinarily C<-1>.
=item int EXPR
+X<int> X<integer> X<truncate> X<trunc> X<floor>
=item int
functions will serve you better than will int().
=item ioctl FILEHANDLE,FUNCTION,SCALAR
+X<ioctl>
Implements the ioctl(2) function. You'll probably first have to say
- require "sys/ioctl.ph"; # probably in $Config{archlib}/ioctl.ph
+ require "sys/ioctl.ph"; # probably in $Config{archlib}/sys/ioctl.ph
to get the correct function definitions. If F<sys/ioctl.ph> doesn't
exist or doesn't have the correct definitions you'll have to roll your
about improper numeric conversions.
=item join EXPR,LIST
+X<join>
Joins the separate strings of LIST into a single string with fields
separated by the value of EXPR, and returns that new string. Example:
first argument. Compare L</split>.
=item keys HASH
+X<keys> X<key>
Returns a list consisting of all the keys of the named hash.
(In scalar context, returns the number of keys.)
See also C<each>, C<values> and C<sort>.
=item kill SIGNAL, LIST
+X<kill> X<signal>
Sends a signal to a list of processes. Returns the number of
processes successfully signaled (which is not necessarily the
$cnt = kill 1, $child1, $child2;
kill 9, @goners;
-If SIGNAL is zero, no signal is sent to the process. This is a
-useful way to check that a child process is alive and hasn't changed
-its UID. See L<perlport> for notes on the portability of this
-construct.
+If SIGNAL is zero, no signal is sent to the process, but the kill(2)
+system call will check whether it's possible to send a signal to it (that
+means, to be brief, that the process is owned by the same user, or we are
+the super-user). This is a useful way to check that a child process is
+alive (even if only as a zombie) and hasn't changed its UID. See
+L<perlport> for notes on the portability of this construct.
Unlike in the shell, if SIGNAL is negative, it kills
process groups instead of processes. (On System V, a negative I<PROCESS>
See L<perlipc/"Signals"> for more details.
=item last LABEL
+X<last> X<break>
=item last
C<redo> work.
=item lc EXPR
+X<lc> X<lowercase>
=item lc
If EXPR is omitted, uses C<$_>.
=item lcfirst EXPR
+X<lcfirst> X<lowercase>
=item lcfirst
If EXPR is omitted, uses C<$_>.
=item length EXPR
+X<length> X<size>
=item length
Note the I<characters>: if the EXPR is in Unicode, you will get the
number of characters, not the number of bytes. To get the length
-in bytes, use C<do { use bytes; length(EXPR) }>, see L<bytes>.
+of the internal string in bytes, use C<bytes::length(EXPR)>, see
+L<bytes>. Note that the internal encoding is variable, and the number
+of bytes usually meaningless. To get the number of bytes that the
+string would have when encoded as UTF-8, use
+C<length(Encoding::encode_utf8(EXPR))>.
=item link OLDFILE,NEWFILE
+X<link>
Creates a new filename linked to the old filename. Returns true for
success, false otherwise.
=item listen SOCKET,QUEUESIZE
+X<listen>
Does the same thing that the listen 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>
You really probably want to be using C<my> instead, because C<local> isn't
what most people think of as "local". See
for details, including issues with tied arrays and hashes.
=item localtime EXPR
+X<localtime> X<ctime>
=item localtime
$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:
$year = sprintf("%02d", $year % 100);
See L<perlport/localtime> for portability concerns.
+The L<Time::gmtime> and L<Time::localtime> modules provides a convenient,
+by-name access mechanism to the gmtime() and localtime() functions,
+respectively.
+
+For a comprehensive date and time representation look at the
+L<DateTime> module on CPAN.
+
=item lock THING
+X<lock>
This function places an advisory lock on a shared variable, or referenced
object contained in I<THING> until the lock goes out of scope.
keyword.) See L<threads>.
=item log EXPR
+X<log> X<logarithm> X<e> X<ln> X<base>
=item log
See also L</exp> for the inverse operation.
=item lstat EXPR
+X<lstat>
=item lstat
The match operator. See L<perlop>.
=item map BLOCK LIST
+X<map>
=item map EXPR,LIST
translates a list of numbers to the corresponding characters. And
- %hash = map { getkey($_) => $_ } @array;
+ %hash = map { get_a_key_for($_) => $_ } @array;
is just a funny way to write
%hash = ();
- foreach $_ (@array) {
- $hash{getkey($_)} = $_;
+ foreach (@array) {
+ $hash{get_a_key_for($_)} = $_;
}
Note that C<$_> is an alias to the list value, so it can be used to
the original list for which the BLOCK or EXPR evaluates to true.
If C<$_> is lexical in the scope where the C<map> appears (because it has
-been declared with C<my $_>) then, in addition to being locally aliased to
-the list elements, C<$_> keeps being lexical inside the block; i.e. it
+been declared with C<my $_>), then, in addition to being locally aliased to
+the list elements, C<$_> keeps being lexical inside the block; that is, it
can't be seen from the outside, avoiding any potential side-effects.
C<{> starts both hash references and blocks, so C<map { ...> could be either
%hash = map ( lc($_), 1 ), @array # evaluates to (1, @array)
-or to force an anon hash constructor use C<+{>
+or to force an anon hash constructor use C<+{>:
@hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end
and you get list of anonymous hashes each with only 1 entry.
=item mkdir FILENAME,MASK
+X<mkdir> X<md> X<directory, create>
=item mkdir FILENAME
this right, so Perl automatically removes all trailing slashes to keep
everyone happy.
+In order to recursively create a directory structure look at
+the C<mkpath> function of the L<File::Path> module.
+
=item msgctl ID,CMD,ARG
+X<msgctl>
Calls the System V IPC function msgctl(2). You'll probably have to say
L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::Semaphore> documentation.
=item msgget KEY,FLAGS
+X<msgget>
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.
=item msgrcv ID,VAR,SIZE,TYPE,FLAGS
+X<msgrcv>
Calls the System V IPC function msgrcv to receive a message from
message queue ID into variable VAR with a maximum message size of
C<IPC::SysV::Msg> documentation.
=item msgsnd ID,MSG,FLAGS
+X<msgsnd>
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
and C<IPC::SysV::Msg> documentation.
=item my EXPR
+X<my>
=item my TYPE EXPR
L<attributes>, and L<Attribute::Handlers>.
=item next LABEL
+X<next> X<continue>
=item next
C<redo> work.
=item no Module VERSION LIST
+X<no>
=item no Module VERSION
=item no Module
+=item no VERSION
+
See the C<use> function, of which C<no> is the opposite.
=item oct EXPR
+X<oct> X<octal> X<hex> X<hexadecimal> X<binary> X<bin>
=item oct
conversion assumes base 10.)
=item open FILEHANDLE,EXPR
+X<open> X<pipe> X<file, open> X<fopen>
=item open FILEHANDLE,MODE,EXPR
that affect how the input and output are processed (see L<open> and
L<PerlIO> for more details). For example
- open(FH, "<:utf8", "file")
+ open(FH, "<:encoding(UTF-8)", "file")
will open the UTF-8 encoded file containing Unicode characters,
-see L<perluniintro>. (Note that if layers are specified in the
-three-arg form then default layers set by the C<open> pragma are
-ignored.)
+see L<perluniintro>. Note that if layers are specified in the
+three-arg form then default layers stored in ${^OPEN} (see L<perlvar>;
+usually set by the B<open> pragma or the switch B<-CioD>) are ignored.
Open returns nonzero upon success, the undefined value otherwise. If
the C<open> involved a pipe, the return value happens to be the pid of
See L</seek> for some details about mixing reading and writing.
=item opendir DIRHANDLE,EXPR
+X<opendir>
Opens a directory named EXPR for processing by C<readdir>, C<telldir>,
C<seekdir>, C<rewinddir>, and C<closedir>. Returns true if successful.
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
=item ord EXPR
+X<ord> X<encoding>
=item ord
uses C<$_>.
For the reverse, see L</chr>.
-See L<perlunicode> and L<encoding> for more about Unicode.
+See L<perlunicode> for more about Unicode.
=item our EXPR
+X<our> X<global>
-=item our EXPR TYPE
+=item our TYPE EXPR
=item our EXPR : ATTRS
L<perlsub/"Private Variables via my()"> for details, and L<fields>,
L<attributes>, and L<Attribute::Handlers>.
-The only currently recognized C<our()> attribute is C<unique> which
-indicates that a single copy of the global is to be used by all
-interpreters should the program happen to be running in a
-multi-interpreter environment. (The default behaviour would be for
-each interpreter to have its own copy of the global.) Examples:
-
- our @EXPORT : unique = qw(foo);
- our %EXPORT_TAGS : unique = (bar => [qw(aa bb cc)]);
- our $VERSION : unique = "1.00";
-
-Note that this attribute also has the effect of making the global
-readonly when the first new interpreter is cloned (for example,
-when the first new thread is created).
-
-Multi-interpreter environments can come to being either through the
-fork() emulation on Windows platforms, or by embedding perl in a
-multi-threaded application. The C<unique> attribute does nothing in
-all other environments.
-
-Warning: the current implementation of this attribute operates on the
-typeglob associated with the variable; this means that C<our $x : unique>
-also has the effect of C<our @x : unique; our %x : unique>. This may be
-subject to change.
-
=item pack TEMPLATE,LIST
+X<pack>
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
H A hex string (high nybble first).
c A signed char (8-bit) value.
- C An unsigned C char (octet) even under Unicode. Should normally not
- be used. See U and W instead.
+ C An unsigned char (octet) value.
W An unsigned char value (can be greater than 255).
s A signed short (16-bit) 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'.)
-
+
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.
P A pointer to a structure (fixed-length string).
u A uuencoded string.
- U A Unicode character number. Encodes to UTF-8 internally
- (or UTF-EBCDIC in EBCDIC platforms).
+ U A Unicode character number. Encodes to a character in character 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,
The C</> template character allows packing and unpacking of a sequence of
items where the packed structure contains a packed item count followed by
the packed items themselves.
-You write I<length-item>C</>I<sequence-item>.
-The I<length-item> can be any C<pack> template letter, and describes
-how the length value is packed. The ones 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> you write I<length-item>C</>I<sequence-item> and the
+I<length-item> describes how the length value is packed. The ones 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>, the I<sequence-item> may have a repeat count, in which case
the minimum of that and the number of available items is used as argument
for the I<length-item>. If it has no repeat count or uses a '*', the number
-of available items is used. For C<unpack> the repeat count is always obtained
-by decoding the packed item count, and the I<sequence-item> must not have a
-repeat count.
+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
+have a repeat count.
If the I<sequence-item> refers to a string type (C<"A">, C<"a"> or C<"Z">),
the I<length-item> is a string length, not a number of strings. If there is
an explicit repeat count for pack, the packed string will be adjusted to that
given length.
- unpack 'W/a', "\04Gurusamy"; gives ('Guru')
- unpack 'a3/A* A*', '007 Bond J '; gives (' Bond', 'J')
- pack 'n/a* w/a','hello,','world'; gives "\000\006hello,\005world"
- pack 'a/W2', ord('a') .. ord('z'); gives '2ab'
+ unpack 'W/a', "\04Gurusamy"; gives ('Guru')
+ unpack 'a3/A A*', '007 Bond J '; gives (' Bond', 'J')
+ unpack 'a3 x2 /A A*', '007: Bond, J.'; gives ('Bond, J', '.')
+ pack 'n/a* w/a','hello,','world'; gives "\000\006hello,\005world"
+ pack 'a/W2', ord('a') .. ord('z'); gives '2ab'
The I<length-item> is not returned explicitly from C<unpack>.
The same template may generally also be used in unpack().
=item package NAMESPACE
+X<package> X<module> X<namespace>
=item package
and classes. See L<perlsub> for other scoping issues.
=item pipe READHANDLE,WRITEHANDLE
+X<pipe>
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
See L<perlvar/$^F>.
=item pop ARRAY
+X<pop> X<stack>
=item pop
Pops and returns the last value of the array, shortening the array by
-one element. Has an effect similar to
-
- $ARRAY[$#ARRAY--]
+one element.
If there are no elements in the array, returns the undefined value
(although this may happen at other times as well). If ARRAY is
array in subroutines, just like C<shift>.
=item pos SCALAR
+X<pos> X<match, position>
=item pos
L<perlop>.
=item print FILEHANDLE LIST
+X<print>
=item print LIST
print { $OK ? STDOUT : STDERR } "stuff\n";
=item printf FILEHANDLE FORMAT, LIST
+X<printf>
=item printf FORMAT, LIST
Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\>
(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,
-the character used for the decimal point in formatted real numbers is
-affected by the LC_NUMERIC locale. See L<perllocale>.
+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
+separator in formatted floating point numbers is affected by the LC_NUMERIC
+locale. 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
error prone.
=item prototype FUNCTION
+X<prototype>
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,
prototype is returned.
=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
$ARRAY[++$#ARRAY] = $value;
}
-but is more efficient. Returns the new number of elements in the array.
+but is more efficient. Returns the number of elements in the array following
+the completed C<push>.
=item q/STRING/
Generalized quotes. See L<perlop/"Regexp Quote-Like Operators">.
=item quotemeta EXPR
+X<quotemeta> X<metacharacter>
=item quotemeta
If EXPR is omitted, uses C<$_>.
=item rand EXPR
+X<rand> X<random>
=item rand
with the wrong number of RANDBITS.)
=item read FILEHANDLE,SCALAR,LENGTH,OFFSET
+X<read> X<file, read>
=item read FILEHANDLE,SCALAR,LENGTH
in that case pretty much any characters can be read.
=item readdir DIRHANDLE
+X<readdir>
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
=item readline EXPR
-Reads from the filehandle whose typeglob is contained in EXPR. In scalar
-context, each call reads and returns the next line, until end-of-file is
-reached, whereupon the subsequent call returns undef. In list context,
-reads until end-of-file is reached and returns a list of lines. Note that
-the notion of "line" used here is however you may have defined it
-with C<$/> or C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">.
+=item readline
+X<readline> X<gets> X<fgets>
+
+Reads from the filehandle whose typeglob is contained in EXPR (or from
+*ARGV if EXPR is not provided). In scalar context, each call reads and
+returns the next line, until end-of-file is reached, whereupon the
+subsequent call returns undef. In list context, reads until end-of-file
+is reached and returns a list of lines. Note that the notion of "line"
+used here is however you may have defined it with C<$/> or
+C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">.
When C<$/> is set to C<undef>, when readline() is in scalar
context (i.e. file slurp mode), and when an empty file is read, it
}
=item readlink EXPR
+X<readlink>
=item readlink
=item readpipe EXPR
+=item readpipe
+X<readpipe>
+
EXPR is executed as a system command.
The collected standard output of the command is returned.
In scalar context, it comes back as a single (potentially
This is the internal function implementing the C<qx/EXPR/>
operator, but you can use it directly. The C<qx/EXPR/>
operator is discussed in more detail in L<perlop/"I/O Operators">.
+If EXPR is omitted, uses C<$_>.
=item recv SOCKET,SCALAR,LENGTH,FLAGS
+X<recv>
Receives a message on a socket. Attempts to receive LENGTH characters
of data into variable SCALAR from the specified SOCKET filehandle.
in that case pretty much any characters can be read.
=item redo LABEL
+X<redo>
=item redo
C<redo> work.
=item ref EXPR
+X<ref> X<reference>
=item ref
REF
GLOB
LVALUE
+ FORMAT
+ IO
+ VSTRING
+ Regexp
If the referenced object has been blessed into a package, then that package
name is returned instead. You can think of C<ref> as a C<typeof> operator.
print "r is not a reference at all.\n";
}
+The return value C<LVALUE> indicates a reference to an lvalue that is not
+a variable. You get this from taking the reference of function calls like
+C<pos()> or C<substr()>. C<VSTRING> is returned if the reference points
+to a L<version string|perldata/"Version Strings">.
+
+The result C<Regexp> indicates that the argument is a regular expression
+resulting from C<qr//>.
+
See also L<perlref>.
=item rename OLDNAME,NEWNAME
+X<rename> X<move> X<mv> X<ren>
Changes the name of a file; an existing file NEWNAME will be
clobbered. Returns true for success, false otherwise.
open files, or pre-existing files. Check L<perlport> and either the
rename(2) manpage or equivalent system documentation for details.
+For a platform independent C<move> function look at the L<File::Copy>
+module.
+
=item require VERSION
+X<require>
=item require EXPR
require 5.6.1; # ditto
require 5.006_001; # ditto; preferred for backwards compatibility
-Otherwise, C<ref> demands that a library file be included if it hasn't already
-been included. The file is included via the do-FILE mechanism, which is
-essentially just a variety of C<eval>. Has semantics similar to the
-following subroutine:
+Otherwise, C<require> demands that a library file be included if it
+hasn't already been included. The file is included via the do-FILE
+mechanism, which is essentially just a variety of C<eval> with the
+caveat that lexical variables in the invoking script will be invisible
+to the included code. Has semantics similar to the following subroutine:
sub require {
my ($filename) = @_;
eval "require $class";
-Now that you understand how C<require> looks for files in the case of
-a bareword argument, there is a little extra functionality going on
-behind the scenes. Before C<require> looks for a "F<.pm>" extension,
-it will first look for a filename with a "F<.pmc>" extension. A file
-with this extension is assumed to be Perl bytecode generated by
-L<B::Bytecode|B::Bytecode>. If this file is found, and its modification
-time is newer than a coinciding "F<.pm>" non-compiled file, it will be
-loaded in place of that non-compiled file ending in a "F<.pm>" extension.
+Now that you understand how C<require> looks for files in the case of a
+bareword argument, there is a little extra functionality going on behind
+the scenes. Before C<require> looks for a "F<.pm>" extension, it will
+first look for a similar filename with a "F<.pmc>" extension. If this file
+is found, it will be loaded in place of any file ending in a "F<.pm>"
+extension.
You can also insert hooks into the import facility, by putting directly
Perl code into the @INC array. There are three forms of hooks: subroutine
walks through @INC and encounters a subroutine, this subroutine gets
called with two parameters, the first being a reference to itself, and the
second the name of the file to be included (e.g. "F<Foo/Bar.pm>"). The
-subroutine should return C<undef> or a filehandle, from which the file to
-include will be read. If C<undef> is returned, C<require> will look at
-the remaining elements of @INC.
+subroutine should return nothing, or a list of up to three values in the
+following order:
+
+=over
+
+=item 1
+
+A filehandle, from which the file will be read.
+
+=item 2
+
+A reference to a subroutine. If there is no filehandle (previous item),
+then this subroutine is expected to generate one line of source code per
+call, writing the line into C<$_> and returning 1, then returning 0 at
+"end of file". If there is a filehandle, then the subroutine will be
+called to act 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
+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> will look at the remaining elements of @INC.
+Note that this file handle must be a real file handle (strictly a typeglob,
+or reference to a typeglob, blessed or unblessed) - tied file handles will be
+ignored and return value 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
If the hook is an object, it must provide an INC method that will be
called as above, the first parameter being the object itself. (Note that
-you must fully qualify the sub's name, as it is always forced into package
-C<main>.) Here is a typical code layout:
+you must fully qualify the sub's name, as unqualified C<INC> is always forced
+into package C<main>.) Here is a typical code layout:
# In Foo.pm
package Foo;
For a yet-more-powerful import facility, see L</use> and L<perlmod>.
=item reset EXPR
+X<reset>
=item reset
See L</my>.
=item return EXPR
+X<return>
=item return
evaluated.)
=item reverse LIST
+X<reverse> X<rev> X<invert>
In list context, returns a list value consisting of the elements
of LIST in the opposite order. In scalar context, concatenates the
%by_name = reverse %by_address; # Invert the hash
=item rewinddir DIRHANDLE
+X<rewinddir>
Sets the current position to the beginning of the directory for the
C<readdir> routine on DIRHANDLE.
=item rindex STR,SUBSTR,POSITION
+X<rindex>
=item rindex STR,SUBSTR
-Works just like index() except that it returns the position of the LAST
+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 at or before that position.
+last occurrence beginning at or before that position.
=item rmdir FILENAME
+X<rmdir> X<rd> X<directory, remove>
=item rmdir
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
+the C<rmtree> function of the L<File::Path> module.
+
=item s///
The substitution operator. See L<perlop>.
+=item say FILEHANDLE LIST
+X<say>
+
+=item say LIST
+
+=item say
+
+Just like C<print>, but implicitly appends a newline.
+C<say LIST> is simply an abbreviation for C<{ local $\ = "\n"; print
+LIST }>.
+
+This keyword is only available when the "say" feature is
+enabled: see L<feature>.
+
=item scalar EXPR
+X<scalar> X<context>
Forces EXPR to be interpreted in scalar context and returns the value
of EXPR.
See L<perlop> for more details on unary operators and the comma operator.
=item seek FILEHANDLE,POSITION,WHENCE
+X<seek> X<fseek> X<filehandle, position>
Sets FILEHANDLE's position, just like the C<fseek> call of C<stdio>.
FILEHANDLE may be an expression whose value gives the name of the
}
=item seekdir DIRHANDLE,POS
+X<seekdir>
Sets the current position for the C<readdir> routine on DIRHANDLE. POS
must be a value returned by C<telldir>. C<seekdir> also has the same caveats
routine.
=item select FILEHANDLE
+X<select> X<filehandle, default>
=item select
-Returns the currently selected filehandle. Sets the current default
-filehandle for output, if FILEHANDLE is supplied. This has two
+Returns the currently selected filehandle. If FILEHANDLE is supplied,
+sets the new current default filehandle for output. This has two
effects: first, a C<write> or a C<print> without a filehandle will
default to this FILEHANDLE. Second, references to variables related to
output will refer to this output channel. For example, if you have to
STDERR->autoflush(1);
=item select RBITS,WBITS,EBITS,TIMEOUT
+X<select>
This calls the select(2) system call with the bit masks specified, which
can be constructed using C<fileno> and C<vec>, along these lines:
is implementation-dependent. See also L<perlport> for notes on the
portability of C<select>.
-On error, C<select> returns C<undef> and sets C<$!>.
+On error, C<select> behaves like the select(2) system call : it returns
+-1 and sets C<$!>.
Note: on some Unixes, the select(2) system call may report a socket file
descriptor as "ready for reading", when actually no data is available,
then only on POSIX systems. You have to use C<sysread> instead.
=item semctl ID,SEMNUM,CMD,ARG
+X<semctl>
Calls the System V IPC function C<semctl>. You'll probably have to say
documentation.
=item semget KEY,NSEMS,FLAGS
+X<semget>
Calls the System V IPC function semget. Returns the semaphore id, or
the undefined value if there is an error. See also
documentation.
=item semop KEY,OPSTRING
+X<semop>
Calls the System V IPC function semop to perform semaphore operations
such as signalling and waiting. OPSTRING must be a packed array of
documentation.
=item send SOCKET,MSG,FLAGS,TO
+X<send>
=item send SOCKET,MSG,FLAGS
in that case pretty much any characters can be sent.
=item setpgrp PID,PGRP
+X<setpgrp> X<group>
Sets the current process group for the specified PID, C<0> for the current
process. Will produce a fatal error if used on a machine that doesn't
C<POSIX::setsid()>.
=item setpriority WHICH,WHO,PRIORITY
+X<setpriority> X<priority> X<nice> X<renice>
Sets the current priority for a process, a process group, or a user.
(See setpriority(2).) Will produce a fatal error if used on a machine
that doesn't implement setpriority(2).
=item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
+X<setsockopt>
Sets the socket option requested. Returns undefined if there is an
-error. OPTVAL may be specified as C<undef> if you don't want to pass an
-argument.
+error. Use integer constants provided by the C<Socket> module for
+LEVEL and OPNAME. Values for LEVEL can also be obtained from
+getprotobyname. OPTVAL might either be a packed string or an integer.
+An integer OPTVAL is shorthand for pack("i", OPTVAL).
+
+An example disabling the Nagle's algorithm for a socket:
+
+ use Socket qw(IPPROTO_TCP TCP_NODELAY);
+ setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1);
=item shift ARRAY
+X<shift>
=item shift
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 of a subroutine and also within the lexical scopes
-established by the C<eval STRING>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>
-and C<END {}> constructs.
+established by the C<eval STRING>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>,
+C<UNITCHECK {}> and C<END {}> constructs.
See also C<unshift>, C<push>, and C<pop>. C<shift> and C<unshift> do the
same thing to the left end of an array that C<pop> and C<push> do to the
right end.
=item shmctl ID,CMD,ARG
+X<shmctl>
Calls the System V IPC function shmctl. You'll probably have to say
See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
=item shmget KEY,SIZE,FLAGS
+X<shmget>
Calls the System V IPC function shmget. Returns the shared memory
segment id, or the undefined value if there is an error.
See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.
=item shmread ID,VAR,POS,SIZE
+X<shmread>
+X<shmwrite>
=item shmwrite ID,STRING,POS,SIZE
C<IPC::SysV> documentation, and the C<IPC::Shareable> module from CPAN.
=item shutdown SOCKET,HOW
+X<shutdown>
Shuts down a socket connection in the manner indicated by HOW, which
has the same interpretation as in the system call of the same name.
processes.
=item sin EXPR
+X<sin> X<sine> X<asin> X<arcsine>
=item sin
sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }
=item sleep EXPR
+X<sleep> X<pause>
=item sleep
See also the POSIX module's C<pause> function.
=item socket SOCKET,DOMAIN,TYPE,PROTOCOL
+X<socket>
Opens a socket of the specified kind and attaches it to filehandle
SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for
value of $^F. See L<perlvar/$^F>.
=item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
+X<socketpair>
Creates an unnamed pair of sockets in the specified domain, of the
specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as
sockets but not socketpair.
=item sort SUBNAME LIST
+X<sort> X<qsort> X<quicksort> X<mergesort>
=item sort BLOCK LIST
in the latter case, it is usually counter-productive to declare $a and
$b as lexicals.
-In either case, the subroutine may not be recursive. The values to be
-compared are always passed by reference and should not be modified.
+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
current collation locale. See L<perllocale>.
+sort() returns aliases into the original list, much as a for loop's index
+variable aliases the list elements. That is, modifying an element of a
+list returned by sort() (for example, in a C<foreach>, C<map> or C<grep>)
+actually modifies the element in the original list. This is usually
+something to be avoided when writing clear code.
+
Perl 5.6 and earlier used a quicksort algorithm to implement sort.
That algorithm was not stable, and I<could> go quadratic. (A I<stable> sort
preserves the input order of elements that compare equal. Although
@result = sort { $a <=> $b } grep { $_ == $_ } @input;
=item splice ARRAY,OFFSET,LENGTH,LIST
+X<splice>
=item splice ARRAY,OFFSET,LENGTH
if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }
=item split /PATTERN/,EXPR,LIMIT
+X<split>
=item split /PATTERN/,EXPR
# @fields is (1, 'A', 2, undef, 3)
=item sprintf FORMAT, LIST
+X<sprintf>
Returns a string formatted by the usual C<printf> conventions of the C
library function C<sprintf>. See below for more details
%E like %e, but using an upper-case "E"
%G like %g, but with an upper-case "E" (if applicable)
%b an unsigned integer, in binary
+ %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
=item flags
one or more of:
+
space prefix positive number with a space
+ prefix positive number with a plus sign
- left-justify within the field
0 use zeros, not spaces, to right-justify
- # prefix non-zero octal with "0", non-zero hex with "0x",
- non-zero binary with "0b"
+ # ensure the leading "0" for any octal,
+ prefix non-zero hexadecimal with "0x" or "0X",
+ prefix non-zero binary with "0b" or "0B"
For example:
- printf '<% d>', 12; # prints "< 12>"
- printf '<%+d>', 12; # prints "<+12>"
- printf '<%6s>', 12; # prints "< 12>"
- printf '<%-6s>', 12; # prints "<12 >"
- printf '<%06s>', 12; # prints "<000012>"
- printf '<%#x>', 12; # prints "<0xc>"
+ printf '<% d>', 12; # prints "< 12>"
+ printf '<%+d>', 12; # prints "<+12>"
+ printf '<%6s>', 12; # prints "< 12>"
+ printf '<%-6s>', 12; # prints "<12 >"
+ printf '<%06s>', 12; # prints "<000012>"
+ printf '<%#o>', 12; # prints "<014>"
+ printf '<%#x>', 12; # prints "<0xc>"
+ printf '<%#X>', 12; # prints "<0XC>"
+ printf '<%#b>', 12; # prints "<0b1100>"
+ printf '<%#B>', 12; # prints "<0B1100>"
+
+When a space and a plus sign are given as the flags at once,
+a plus sign is used to prefix a positive number.
+
+ printf '<%+ d>', 12; # prints "<+12>"
+ printf '<% +d>', 12; # prints "<+12>"
+
+When the # flag and a precision are given in the %o conversion,
+the precision is incremented if it's necessary for the leading "0".
+
+ printf '<%#.5o>', 012; # prints "<00012>"
+ printf '<%#.5o>', 012345; # prints "<012345>"
+ printf '<%#.0o>', 0; # prints "<0>"
=item vector flag
-The vector flag C<v>, optionally specifying the join string to use.
-This flag tells perl to interpret the supplied string as a vector
-of integers, one for each character in the string, separated by
-a given string (a dot C<.> by default). This can be useful for
-displaying ordinal values of characters in arbitrary strings:
+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
+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
+characters in arbitrary strings:
+ printf "%vd", "AB\x{100}"; # prints "65.66.256"
printf "version is v%vd\n", $^V; # Perl's version
Put an asterisk C<*> before the C<v> to override the string to
effect as the C<-> flag: left-justification.
=item precision, or maximum width
+X<precision>
You can specify a precision (for numeric conversions) or a maximum
width (for string conversions) by specifying a C<.> followed by a number.
printf '<%.4g>', 100.01; # prints "<100>"
For integer conversions, specifying a precision implies that the
-output of the number itself should be zero-padded to this width:
+output of the number itself should be zero-padded to this width,
+where the 0 flag is ignored:
+
+ printf '<%.6d>', 1; # prints "<000001>"
+ printf '<%+.6d>', 1; # prints "<+000001>"
+ printf '<%-10.6d>', 1; # prints "<000001 >"
+ printf '<%10.6d>', 1; # prints "< 000001>"
+ printf '<%010.6d>', 1; # prints "< 000001>"
+ printf '<%+10.6d>', 1; # prints "< +000001>"
printf '<%.6x>', 1; # prints "<000001>"
printf '<%#.6x>', 1; # prints "<0x000001>"
printf '<%-10.6x>', 1; # prints "<000001 >"
+ printf '<%10.6x>', 1; # prints "< 000001>"
+ printf '<%010.6x>', 1; # prints "< 000001>"
+ printf '<%#10.6x>', 1; # prints "< 0x000001>"
For string conversions, specifying a precision truncates the string
to fit in the specified width:
printf '<%.6x>', 1; # prints "<000001>"
printf '<%.*x>', 6, 1; # prints "<000001>"
+If a precision obtained through C<*> is negative, it has the same
+effect as no precision.
+
+ printf '<%.*s>', 7, "string"; # prints "<string>"
+ printf '<%.*s>', 3, "string"; # prints "<str>"
+ printf '<%.*s>', 0, "string"; # prints "<>"
+ printf '<%.*s>', -1, "string"; # prints "<string>"
+
+ printf '<%.*d>', 1, 0; # prints "<0>"
+ printf '<%.*d>', 0, 0; # prints "<>"
+ printf '<%.*d>', -1, 0; # prints "<0>"
+
You cannot currently get the precision from a specified number,
but it is intended that this will be possible in the future using
e.g. C<.*2$>:
=back
-If C<use locale> is in effect, the character used for the decimal
-point in formatted real numbers is affected by the LC_NUMERIC locale.
-See L<perllocale>.
+If C<use locale> 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 EXPR
+X<sqrt> X<root> X<square root>
=item sqrt
print sqrt(-2); # prints 1.4142135623731i
=item srand EXPR
+X<srand> X<seed> X<randseed>
=item srand
one-third of the time. So don't do that.
=item stat FILEHANDLE
+X<stat> X<file, status> X<ctime>
=item stat EXPR
+=item stat DIRHANDLE
+
=item stat
Returns a 13-element list giving the status info for a file, either
-the file opened via FILEHANDLE, or named by EXPR. If EXPR is omitted,
-it stats C<$_>. Returns a null list if the stat fails. Typically used
-as follows:
+the file opened via FILEHANDLE or DIRHANDLE, or named by EXPR. If EXPR is
+omitted, it stats C<$_>. Returns a null list if the stat fails. Typically
+used as follows:
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
$atime,$mtime,$ctime,$blksize,$blocks)
or failure, and, if successful, sets the information associated with
the special filehandle C<_>.
-The File::stat module provides a convenient, by-name access mechanism:
+The L<File::stat> module provides a convenient, by-name access mechanism:
use File::stat;
$sb = stat($filename);
printf "Permissions are %04o\n", S_IMODE($mode), "\n";
$is_setuid = $mode & S_ISUID;
- $is_setgid = S_ISDIR($mode);
+ $is_directory = S_ISDIR($mode);
You could write the last two using the C<-u> and C<-d> operators.
The commonly available C<S_IF*> constants are
# File types. Not necessarily all are available on your system.
- S_IFREG S_IFDIR S_IFLNK S_IFBLK S_ISCHR 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.
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.
+=item state EXPR
+X<state>
+
+=item state TYPE EXPR
+
+=item state EXPR : ATTRS
+
+=item state TYPE EXPR : ATTRS
+
+C<state> declares a lexically scoped variable, just like C<my> does.
+However, those variables will never be reinitialized, contrary to
+lexical variables that are reinitialized each time their enclosing block
+is entered.
+
+C<state> variables are only enabled when the C<feature 'state'> pragma is
+in effect. See L<feature>.
+
=item study SCALAR
+X<study>
=item study
}
=item sub NAME BLOCK
+X<sub>
=item sub NAME (PROTO) BLOCK
information about attributes.
=item substr EXPR,OFFSET,LENGTH,REPLACEMENT
+X<substr> X<substring> X<mid> X<left> X<right>
=item substr EXPR,OFFSET,LENGTH
everything to 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 $color = substr $s, 4, 5; # black
+ my $middle = substr $s, 4, -11; # black cat climbed the
+ my $end = substr $s, 14; # climbed the green tree
+ my $tail = substr $s, -4; # tree
+ my $z = substr $s, -4, 2; # tr
+
You can use the substr() function as an lvalue, in which case EXPR
must itself be an lvalue. If you assign something shorter than LENGTH,
the string will shrink, and if you assign something longer than LENGTH,
parts of the EXPR and return what was there before in one operation,
just as you can with splice().
+ 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
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
unspecified.
=item symlink OLDFILE,NEWFILE
+X<symlink> X<link> X<symbolic link> X<link, symbolic>
Creates a new filename symbolically linked to the old filename.
Returns C<1> for success, C<0> otherwise. On systems that don't support
$symlink_exists = eval { symlink("",""); 1 };
=item syscall NUMBER, LIST
+X<syscall> X<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
problem by using C<pipe> instead.
=item sysopen FILEHANDLE,FILENAME,MODE
+X<sysopen>
=item sysopen FILEHANDLE,FILENAME,MODE,PERMS
Some of the most common values are C<O_RDONLY> for opening the file in
read-only mode, C<O_WRONLY> for opening the file in write-only mode,
and C<O_RDWR> for opening the file in read-write mode.
+X<O_RDONLY> X<O_RDWR> X<O_WRONLY>
For historical reasons, some values work on almost every system
supported by perl: zero means read-only, one means write-only, and two
the PERMS argument to C<sysopen>, Perl uses the octal value C<0666>.
These permission values need to be in octal, and are modified by your
process's current C<umask>.
+X<O_CREAT>
In many systems the C<O_EXCL> flag is available for opening files in
exclusive mode. This is B<not> locking: exclusiveness means here that
is set as well. Setting C<O_CREAT|O_EXCL> prevents the file from
being opened if it is a symbolic link. It does not protect against
symbolic links in the file's path.
+X<O_EXCL>
Sometimes you may want to truncate an already-existing file. This
can be done using the C<O_TRUNC> flag. The behavior of
C<O_TRUNC> with C<O_RDONLY> is undefined.
+X<O_TRUNC>
You should seldom if ever use C<0644> as argument to C<sysopen>, because
that takes away the user's option to have a more permissive umask.
See L<perlopentut> for a kinder, gentler explanation of opening files.
=item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
+X<sysread>
=item sysread FILEHANDLE,SCALAR,LENGTH
See L</binmode>, L</open>, and the C<open> pragma, L<open>.
=item sysseek FILEHANDLE,POSITION,WHENCE
+X<sysseek> X<lseek>
Sets FILEHANDLE's system position in bytes using the system call
lseek(2). FILEHANDLE may be an expression whose value gives the name
the new position.
=item system LIST
+X<system> X<shell>
=item system PROGRAM LIST
of C<IO::Handle> on any open handles.
The return value is the exit status of the program as returned by the
-C<wait> call. To get the actual exit value, shift right by eight (see below).
-See also L</exec>. This is I<not> what you want to use to capture
+C<wait> call. To get the actual exit value, shift right by eight (see
+below). See also L</exec>. This is I<not> what you want to use to capture
the output from a command, for that you should use merely backticks or
C<qx//>, as described in L<perlop/"`STRING`">. Return value of -1
-indicates a failure to start the program (inspect $! for the reason).
+indicates a failure to start the program or an error of the wait(2) system
+call (inspect $! for the reason).
Like C<exec>, C<system> allows you to lie to a program about its name if
you use the C<system PROGRAM LIST> syntax. Again, see L</exec>.
See L<perlop/"`STRING`"> and L</exec> for details.
=item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
+X<syswrite>
=item syswrite FILEHANDLE,SCALAR,LENGTH
See L</binmode>, L</open>, and the C<open> pragma, L<open>.
=item tell FILEHANDLE
+X<tell>
=item tell
Those functions ignore the buffering, while tell() does not.
=item telldir DIRHANDLE
+X<telldir>
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
compaction as the corresponding system library routine.
=item tie VARIABLE,CLASSNAME,LIST
+X<tie>
This function binds a variable to a package class that will provide the
implementation for the variable. VARIABLE is the name of the variable
For further details see L<perltie>, L<"tied VARIABLE">.
=item tied VARIABLE
+X<tied>
Returns a reference to the object underlying VARIABLE (the same value
that was originally returned by the C<tie> call that bound the variable
package.
=item time
+X<time> X<epoch>
Returns the number of non-leap seconds since whatever time the system
considers to be the epoch, suitable for feeding to C<gmtime> and
1904 in the current local time zone for its epoch.
For measuring time in better granularity than one second,
-you may use either the Time::HiRes module (from CPAN, and starting from
+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 date and time processing look at the many related modules on CPAN.
+For a comprehensive date and time representation look at the
+L<DateTime> module.
+
=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.
In scalar context, C<times> returns C<$user>.
+Note that times for children are included only after they terminate.
+
=item tr///
The transliteration operator. Same as C<y///>. See L<perlop>.
=item truncate FILEHANDLE,LENGTH
+X<truncate>
=item truncate EXPR,LENGTH
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> before writing to the file.
+
=item uc EXPR
+X<uc> X<uppercase> X<toupper>
=item uc
If EXPR is omitted, uses C<$_>.
=item ucfirst EXPR
+X<ucfirst> X<uppercase>
=item ucfirst
If EXPR is omitted, uses C<$_>.
=item umask EXPR
+X<umask>
=item umask
string of octal digits. See also L</oct>, if all you have is a string.
=item undef EXPR
+X<undef> X<undefine>
=item undef
Note that this is a unary operator, not a list operator.
=item unlink LIST
+X<unlink> X<delete> X<remove> X<rm> X<del>
=item unlink
unlink @goners;
unlink <*.bak>;
-Note: C<unlink> will not delete directories unless you are superuser and
-the B<-U> flag is supplied to Perl. Even if these conditions are
+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 conditions are
met, be warned that unlinking a directory can inflict damage on your
-filesystem. Use C<rmdir> instead.
+filesystem. Finally, using C<unlink> on directories is not supported on
+many operating systems. Use C<rmdir> instead.
If LIST is omitted, uses C<$_>.
=item unpack TEMPLATE,EXPR
+X<unpack>
=item unpack TEMPLATE
See L</pack> for more examples and notes.
=item untie VARIABLE
+X<untie>
Breaks the binding between a variable and a package. (See C<tie>.)
Has no effect if the variable is not tied.
=item unshift ARRAY,LIST
+X<unshift>
Does the opposite of a C<shift>. Or the opposite of a C<push>,
depending on how you look at it. Prepends list to the front of the
reverse.
=item use Module VERSION LIST
+X<use> X<module> X<import>
=item use Module VERSION
except that Module I<must> be a bareword.
-VERSION may be either a numeric argument such as 5.006, which will be
-compared to C<$]>, or a literal of the form v5.6.1, which will be compared
-to C<$^V> (aka $PERL_VERSION. A fatal error is produced if VERSION is
-greater than the version of the current Perl interpreter; Perl will not
-attempt to parse the rest of the file. Compare with L</require>, which can
-do a similar check at run time.
+In the peculiar C<use VERSION> form, VERSION may be either a numeric
+argument such as 5.006, which will be compared to C<$]>, or a literal of
+the form v5.6.1, which will be compared to C<$^V> (aka $PERL_VERSION). A
+fatal error is produced if VERSION is greater than the version of the
+current Perl interpreter; Perl will not attempt to parse the rest of the
+file. Compare with L</require>, which can do a similar check at run time.
+Symmetrically, C<no VERSION> allows you to specify that you want a version
+of perl older than the specified one.
Specifying VERSION as a literal of the form v5.6.1 should generally be
avoided, because it leads to misleading error messages under earlier
C<use>ing library modules that have changed in incompatible ways from
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>.
+
The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The
C<require> makes sure the module is loaded into memory if it hasn't been
yet. The C<import> is not a builtin--it's just an ordinary static method
functionality from the command-line.
=item utime LIST
+X<utime>
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
described when they are both C<undef>. This case will also trigger an
uninitialized warning.
+On systems that support futimes, you might pass file handles among the
+files. On systems that don't support futimes, passing file handles
+produces a fatal error at run time. The file handles must be passed
+as globs or references to be recognized. Barewords are considered
+file names.
+
=item values HASH
+X<values>
Returns a list consisting of all the values of the named hash.
(In a scalar context, returns the number of values.)
See also C<keys>, C<each>, and C<sort>.
=item vec EXPR,OFFSET,BITS
+X<vec> X<bit> X<bit vector>
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
extend the string with sufficiently many zero bytes. It is an error
to try to write off the beginning of the string (i.e. negative OFFSET).
-The string should not contain any character with the value > 255 (which
-can only happen if you're using UTF-8 encoding). If it does, it will be
-treated as something that is not UTF-8 encoded. When the C<vec> was
-assigned to, other parts of your program will also no longer consider the
-string to be UTF-8 encoded. In other words, if you do have such characters
-in your string, vec() will operate on the actual byte string, and not the
-conceptual character string.
+If the string happens to be encoded as UTF-8 internally (and thus has
+the UTF8 flag set), this is ignored by C<vec>, and it operates on the
+internal byte string, not the conceptual character string, even if you
+only have characters with values less than 256.
Strings created with C<vec> can also be manipulated with the logical
operators C<|>, C<&>, C<^>, and C<~>. These operators will assume a bit
vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001
=item wait
+X<wait>
Behaves like the wait(2) system call on your system: it waits for a child
process to terminate and returns the pid of the deceased process, or
being automatically reaped, as described in L<perlipc>.
=item waitpid PID,FLAGS
+X<waitpid>
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
#...
do {
$kid = waitpid(-1, WNOHANG);
- } until $kid > 0;
+ } while $kid > 0;
then you can do a non-blocking wait for all pending zombie processes.
Non-blocking wait is available on machines supporting either the
and for other examples.
=item wantarray
+X<wantarray> X<context>
Returns true if the context of the currently executing subroutine or
C<eval> is looking for a list value. Returns false if the context is
return wantarray ? @a : "@a";
C<wantarray()>'s result is unspecified in the top level of a file,
-in a C<BEGIN>, C<CHECK>, C<INIT> or C<END> block, or in a C<DESTROY>
-method.
+in a C<BEGIN>, C<UNITCHECK>, C<CHECK>, C<INIT> or C<END> block, or
+in a C<DESTROY> method.
This function should have been named wantlist() instead.
=item warn LIST
+X<warn> X<warning> X<STDERR>
-Produces a message on STDERR just like C<die>, but doesn't exit or throw
-an exception.
+Prints the value of LIST to STDERR. If the last element of LIST does
+not end in a newline, it appends the same file/line number text as C<die>
+does.
If LIST is empty and C<$@> already contains a value (typically from a
previous eval) that value is used after appending C<"\t...caught">
carp() and cluck() functions.
=item write FILEHANDLE
+X<write>
=item write EXPR