path: root/ext/POSIX/lib/POSIX.pod

=head1 NAME

POSIX - Perl interface to IEEE Std 1003.1

=head1 SYNOPSIS

    use POSIX ();
    use POSIX qw(setsid);
    use POSIX qw(:errno_h :fcntl_h);

    printf "EINTR is %d\n", EINTR;

    $sess_id = POSIX::setsid();

    $fd = POSIX::open($path, O_CREAT|O_EXCL|O_WRONLY, 0644);
	# note: that's a filedescriptor, *NOT* a filehandle

=head1 DESCRIPTION

The POSIX module permits you to access all (or nearly all) the standard
POSIX 1003.1 identifiers.  Many of these identifiers have been given Perl-ish
interfaces.

I<Everything is exported by default> with the exception of any POSIX
functions with the same name as a built-in Perl function, such as
C<abs>, C<alarm>, C<rmdir>, C<write>, etc.., which will be exported
only if you ask for them explicitly.  This is an unfortunate backwards
compatibility feature.  You can stop the exporting by saying S<C<use
POSIX ()>> and then use the fully qualified names (I<e.g.>, C<POSIX::SEEK_END>),
or by giving an explicit import list.  If you do neither, and opt for the
default, S<C<use POSIX;>> has to import I<553 symbols>.

This document gives a condensed list of the features available in the POSIX
module.  Consult your operating system's manpages for general information on
most features.  Consult L<perlfunc> for functions which are noted as being
identical to Perl's builtin functions.

The first section describes POSIX functions from the 1003.1 specification.
The second section describes some classes for signal objects, TTY objects,
and other miscellaneous objects.  The remaining sections list various
constants and macros in an organization which roughly follows IEEE Std
1003.1b-1993.

=head1 CAVEATS

A few functions are not implemented because they are C specific.  If you
attempt to call these, they will print a message telling you that they
aren't implemented, and suggest using the Perl equivalent, should one
exist.  For example, trying to access the C<setjmp()> call will elicit the
message "C<setjmp() is C-specific: use eval {} instead>".

Furthermore, some evil vendors will claim 1003.1 compliance, but in fact
are not so: they will not pass the PCTS (POSIX Compliance Test Suites).
For example, one vendor may not define C<EDEADLK>, or the semantics of the
errno values set by C<open(2)> might not be quite right.  Perl does not
attempt to verify POSIX compliance.  That means you can currently
successfully say "use POSIX",  and then later in your program you find
that your vendor has been lax and there's no usable C<ICANON> macro after
all.  This could be construed to be a bug.

=head1 FUNCTIONS

=over 8

=item C<_exit>

This is identical to the C function C<_exit()>.  It exits the program
immediately which means among other things buffered I/O is B<not> flushed.

Note that when using threads and in Linux this is B<not> a good way to
exit a thread because in Linux processes and threads are kind of the
same thing (Note: while this is the situation in early 2003 there are
projects under way to have threads with more POSIXly semantics in Linux).
If you want not to return from a thread, detach the thread.

=item C<abort>

This is identical to the C function C<abort()>.  It terminates the
process with a C<SIGABRT> signal unless caught by a signal handler or
if the handler does not return normally (it e.g.  does a C<longjmp>).

=item C<abs>

This is identical to Perl's builtin C<abs()> function, returning
the absolute value of its numerical argument.

=item C<access>

Determines the accessibility of a file.

	if( POSIX::access( "/", &POSIX::R_OK ) ){
		print "have read permission\n";
	}

Returns C<undef> on failure.  Note: do not use C<access()> for
security purposes.  Between the C<access()> call and the operation
you are preparing for the permissions might change: a classic
I<race condition>.

=item C<acos>

This is identical to the C function C<acos()>, returning
the arcus cosine of its numerical argument.  See also L<Math::Trig>.

=item C<alarm>

This is identical to Perl's builtin C<alarm()> function,
either for arming or disarming the C<SIGARLM> timer.

=item C<asctime>

This is identical to the C function C<asctime()>.  It returns
a string of the form

	"Fri Jun  2 18:22:13 2000\n\0"

and it is called thusly

	$asctime = asctime($sec, $min, $hour, $mday, $mon,
			   $year, $wday, $yday, $isdst);

The C<$mon> is zero-based: January equals C<0>.  The C<$year> is
1900-based: 2001 equals C<101>.  C<$wday> and C<$yday> default to zero
(and are usually ignored anyway), and C<$isdst> defaults to -1.

=item C<asin>

This is identical to the C function C<asin()>, returning
the arcus sine of its numerical argument.  See also L<Math::Trig>.

=item C<assert>

Unimplemented, but you can use L<perlfunc/die> and the L<Carp> module
to achieve similar things.

=item C<atan>

This is identical to the C function C<atan()>, returning the
arcus tangent of its numerical argument.  See also L<Math::Trig>.

=item C<atan2>

This is identical to Perl's builtin C<atan2()> function, returning
the arcus tangent defined by its two numerical arguments, the I<y>
coordinate and the I<x> coordinate.  See also L<Math::Trig>.

=item C<atexit>

C<atexit()> is C-specific: use C<END {}> instead, see L<perlsub>.

=item C<atof>

C<atof()> is C-specific.  Perl converts strings to numbers transparently.
If you need to force a scalar to a number, add a zero to it.

=item C<atoi>

C<atoi()> is C-specific.  Perl converts strings to numbers transparently.
If you need to force a scalar to a number, add a zero to it.
If you need to have just the integer part, see L<perlfunc/int>.

=item C<atol>

C<atol()> is C-specific.  Perl converts strings to numbers transparently.
If you need to force a scalar to a number, add a zero to it.
If you need to have just the integer part, see L<perlfunc/int>.

=item C<bsearch>

C<bsearch()> not supplied.  For doing binary search on wordlists,
see L<Search::Dict>.

=item C<calloc>

C<calloc()> is C-specific.  Perl does memory management transparently.

=item C<ceil>

This is identical to the C function C<ceil()>, returning the smallest
integer value greater than or equal to the given numerical argument.

=item C<chdir>

This is identical to Perl's builtin C<chdir()> function, allowing
one to change the working (default) directory, see L<perlfunc/chdir>.

=item C<chmod>

This is identical to Perl's builtin C<chmod()> function, allowing
one to change file and directory permissions, see L<perlfunc/chmod>.

=item C<chown>

This is identical to Perl's builtin C<chown()> function, allowing one
to change file and directory owners and groups, see L<perlfunc/chown>.

=item C<clearerr>

Use the method C<IO::Handle::clearerr()> instead, to reset the error
state (if any) and EOF state (if any) of the given stream.

=item C<clock>

This is identical to the C function C<clock()>, returning the
amount of spent processor time in microseconds.

=item C<close>

Close the file.  This uses file descriptors such as those obtained by calling
C<POSIX::open>.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	POSIX::close( $fd );

Returns C<undef> on failure.

See also L<perlfunc/close>.

=item C<closedir>

This is identical to Perl's builtin C<closedir()> function for closing
a directory handle, see L<perlfunc/closedir>.

=item C<cos>

This is identical to Perl's builtin C<cos()> function, for returning
the cosine of its numerical argument, see L<perlfunc/cos>.
See also L<Math::Trig>.

=item C<cosh>

This is identical to the C function C<cosh()>, for returning
the hyperbolic cosine of its numeric argument.  See also L<Math::Trig>.

=item C<creat>

Create a new file.  This returns a file descriptor like the ones returned by
C<POSIX::open>.  Use C<POSIX::close> to close the file.

	$fd = POSIX::creat( "foo", 0611 );
	POSIX::close( $fd );

See also L<perlfunc/sysopen> and its C<O_CREAT> flag.

=item C<ctermid>

Generates the path name for the controlling terminal.

	$path = POSIX::ctermid();

=item C<ctime>

This is identical to the C function C<ctime()> and equivalent
to C<asctime(localtime(...))>, see L</asctime> and L</localtime>.

=item C<cuserid>

Get the login name of the owner of the current process.

	$name = POSIX::cuserid();

=item C<difftime>

This is identical to the C function C<difftime()>, for returning
the time difference (in seconds) between two times (as returned
by C<time()>), see L</time>.

=item C<div>

C<div()> is C-specific, use L<perlfunc/int> on the usual C</> division and
the modulus C<%>.

=item C<dup>

This is similar to the C function C<dup()>, for duplicating a file
descriptor.

This uses file descriptors such as those obtained by calling
C<POSIX::open>.

Returns C<undef> on failure.

=item C<dup2>

This is similar to the C function C<dup2()>, for duplicating a file
descriptor to an another known file descriptor.

This uses file descriptors such as those obtained by calling
C<POSIX::open>.

Returns C<undef> on failure.

=item C<errno>

Returns the value of errno.

	$errno = POSIX::errno();

This identical to the numerical values of the C<$!>, see L<perlvar/$ERRNO>.

=item C<execl>

C<execl()> is C-specific, see L<perlfunc/exec>.

=item C<execle>

C<execle()> is C-specific, see L<perlfunc/exec>.

=item C<execlp>

C<execlp()> is C-specific, see L<perlfunc/exec>.

=item C<execv>

C<execv()> is C-specific, see L<perlfunc/exec>.

=item C<execve>

C<execve()> is C-specific, see L<perlfunc/exec>.

=item C<execvp>

C<execvp()> is C-specific, see L<perlfunc/exec>.

=item C<exit>

This is identical to Perl's builtin C<exit()> function for exiting the
program, see L<perlfunc/exit>.

=item C<exp>

This is identical to Perl's builtin C<exp()> function for
returning the exponent (I<e>-based) of the numerical argument,
see L<perlfunc/exp>.

=item C<fabs>

This is identical to Perl's builtin C<abs()> function for returning
the absolute value of the numerical argument, see L<perlfunc/abs>.

=item C<fclose>

Use method C<IO::Handle::close()> instead, or see L<perlfunc/close>.

=item C<fcntl>

This is identical to Perl's builtin C<fcntl()> function,
see L<perlfunc/fcntl>.

=item C<fdopen>

Use method C<IO::Handle::new_from_fd()> instead, or see L<perlfunc/open>.

=item C<feof>

Use method C<IO::Handle::eof()> instead, or see L<perlfunc/eof>.

=item C<ferror>

Use method C<IO::Handle::error()> instead.

=item C<fflush>

Use method C<IO::Handle::flush()> instead.
See also C<L<perlvar/$OUTPUT_AUTOFLUSH>>.

=item C<fgetc>

Use method C<IO::Handle::getc()> instead, or see L<perlfunc/read>.

=item C<fgetpos>

Use method C<IO::Seekable::getpos()> instead, or see L<perlfunc/seek>.

=item C<fgets>

Use method C<IO::Handle::gets()> instead.  Similar to E<lt>E<gt>, also known
as L<perlfunc/readline>.

=item C<fileno>

Use method C<IO::Handle::fileno()> instead, or see L<perlfunc/fileno>.

=item C<floor>

This is identical to the C function C<floor()>, returning the largest
integer value less than or equal to the numerical argument.

=item C<fmod>

This is identical to the C function C<fmod()>.

	$r = fmod($x, $y);

It returns the remainder C<$r = $x - $n*$y>, where C<$n = trunc($x/$y)>.
The C<$r> has the same sign as C<$x> and magnitude (absolute value)
less than the magnitude of C<$y>.

=item C<fopen>

Use method C<IO::File::open()> instead, or see L<perlfunc/open>.

=item C<fork>

This is identical to Perl's builtin C<fork()> function
for duplicating the current process, see L<perlfunc/fork>
and L<perlfork> if you are in Windows.

=item C<fpathconf>

Retrieves the value of a configurable limit on a file or directory.  This
uses file descriptors such as those obtained by calling C<POSIX::open>.

The following will determine the maximum length of the longest allowable
pathname on the filesystem which holds F</var/foo>.

	$fd = POSIX::open( "/var/foo", &POSIX::O_RDONLY );
	$path_max = POSIX::fpathconf($fd, &POSIX::_PC_PATH_MAX);

Returns C<undef> on failure.

=item C<fprintf>

C<fprintf()> is C-specific, see L<perlfunc/printf> instead.

=item C<fputc>

C<fputc()> is C-specific, see L<perlfunc/print> instead.

=item C<fputs>

C<fputs()> is C-specific, see L<perlfunc/print> instead.

=item C<fread>

C<fread()> is C-specific, see L<perlfunc/read> instead.

=item C<free>

C<free()> is C-specific.  Perl does memory management transparently.

=item C<freopen>

C<freopen()> is C-specific, see L<perlfunc/open> instead.

=item C<frexp>

Return the mantissa and exponent of a floating-point number.

	($mantissa, $exponent) = POSIX::frexp( 1.234e56 );

=item C<fscanf>

C<fscanf()> is C-specific, use E<lt>E<gt> and regular expressions instead.

=item C<fseek>

Use method C<IO::Seekable::seek()> instead, or see L<perlfunc/seek>.

=item C<fsetpos>

Use method C<IO::Seekable::setpos()> instead, or seek L<perlfunc/seek>.

=item C<fstat>

Get file status.  This uses file descriptors such as those obtained by
calling C<POSIX::open>.  The data returned is identical to the data from
Perl's builtin C<stat> function.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	@stats = POSIX::fstat( $fd );

=item C<fsync>

Use method C<IO::Handle::sync()> instead.

=item C<ftell>

Use method C<IO::Seekable::tell()> instead, or see L<perlfunc/tell>.

=item C<fwrite>

C<fwrite()> is C-specific, see L<perlfunc/print> instead.

=item C<getc>

This is identical to Perl's builtin C<getc()> function,
see L<perlfunc/getc>.

=item C<getchar>

Returns one character from STDIN.  Identical to Perl's C<getc()>,
see L<perlfunc/getc>.

=item C<getcwd>

Returns the name of the current working directory.
See also L<Cwd>.

=item C<getegid>

Returns the effective group identifier.  Similar to Perl' s builtin
variable C<$(>, see L<perlvar/$EGID>.

=item C<getenv>

Returns the value of the specified environment variable.
The same information is available through the C<%ENV> array.

=item C<geteuid>

Returns the effective user identifier.  Identical to Perl's builtin C<$E<gt>>
variable, see L<perlvar/$EUID>.

=item C<getgid>

Returns the user's real group identifier.  Similar to Perl's builtin
variable C<$)>, see L<perlvar/$GID>.

=item C<getgrgid>

This is identical to Perl's builtin C<getgrgid()> function for
returning group entries by group identifiers, see
L<perlfunc/getgrgid>.

=item C<getgrnam>

This is identical to Perl's builtin C<getgrnam()> function for
returning group entries by group names, see L<perlfunc/getgrnam>.

=item C<getgroups>

Returns the ids of the user's supplementary groups.  Similar to Perl's
builtin variable C<$)>, see L<perlvar/$GID>.

=item C<getlogin>

This is identical to Perl's builtin C<getlogin()> function for
returning the user name associated with the current session, see
L<perlfunc/getlogin>.

=item C<getpgrp>

This is identical to Perl's builtin C<getpgrp()> function for
returning the process group identifier of the current process, see
L<perlfunc/getpgrp>.

=item C<getpid>

Returns the process identifier.  Identical to Perl's builtin
variable C<$$>, see L<perlvar/$PID>.

=item C<getppid>

This is identical to Perl's builtin C<getppid()> function for
returning the process identifier of the parent process of the current
process , see L<perlfunc/getppid>.

=item C<getpwnam>

This is identical to Perl's builtin C<getpwnam()> function for
returning user entries by user names, see L<perlfunc/getpwnam>.

=item C<getpwuid>

This is identical to Perl's builtin C<getpwuid()> function for
returning user entries by user identifiers, see L<perlfunc/getpwuid>.

=item C<gets>

Returns one line from C<STDIN>, similar to E<lt>E<gt>, also known
as the C<readline()> function, see L<perlfunc/readline>.

B<NOTE>: if you have C programs that still use C<gets()>, be very
afraid.  The C<gets()> function is a source of endless grief because
it has no buffer overrun checks.  It should B<never> be used.  The
C<fgets()> function should be preferred instead.

=item C<getuid>

Returns the user's identifier.  Identical to Perl's builtin C<$E<lt>> variable,
see L<perlvar/$UID>.

=item C<gmtime>

This is identical to Perl's builtin C<gmtime()> function for
converting seconds since the epoch to a date in Greenwich Mean Time,
see L<perlfunc/gmtime>.

=item C<isalnum>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:alnum:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

You may want to use the C<L<E<sol>\wE<sol>|perlrecharclass/Word
characters>> construct instead.

=item C<isalpha>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:alpha:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

=item C<isatty>

Returns a boolean indicating whether the specified filehandle is connected
to a tty.  Similar to the C<-t> operator, see L<perlfunc/-X>.

=item C<iscntrl>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:cntrl:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

=item C<isdigit>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:digit:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

You may want to use the C<L<E<sol>\dE<sol>|perlrecharclass/Digits>>
construct instead.

=item C<isgraph>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:graph:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

=item C<islower>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:lower:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

Do B<not> use C</[a-z]/> unless you don't care about the current locale.

=item C<isprint>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:print:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

=item C<ispunct>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:punct:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

=item C<isspace>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:space:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

You may want to use the C<L<E<sol>\sE<sol>|perlrecharclass/Whitespace>>
construct instead.

=item C<isupper>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:upper:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

Do B<not> use C</[A-Z]/> unless you don't care about the current locale.

=item C<isxdigit>

Deprecated function whose use raises a warning, and which is slated to
be removed in a future Perl version.  It is very similar to matching
against S<C<qr/ ^ [[:xdigit:]]+ $ /x>>, which you should convert to use
instead.  The function is deprecated because 1) it doesn't handle UTF-8
encoded strings properly; and 2) it returns C<TRUE> even if the input is
the empty string.  The function return is always based on the current
locale, whereas using locale rules is optional with the regular
expression, based on pragmas in effect and pattern modifiers (see
L<perlre/Character set modifiers> and L<perlre/Which character set
modifier is in effect?>).

The function returns C<TRUE> if the input string is empty, or if the
corresponding C function returns C<TRUE> for every byte in the string.

=item C<kill>

This is identical to Perl's builtin C<kill()> function for sending
signals to processes (often to terminate them), see L<perlfunc/kill>.

=item C<labs>

(For returning absolute values of long integers.)
C<labs()> is C-specific, see L<perlfunc/abs> instead.

=item C<lchown>

This is identical to the C function, except the order of arguments is
consistent with Perl's builtin C<chown()> with the added restriction
of only one path, not an list of paths.  Does the same thing as the 
C<chown()> function but changes the owner of a symbolic link instead 
of the file the symbolic link points to.

=item C<ldexp>

This is identical to the C function C<ldexp()>
for multiplying floating point numbers with powers of two.

	$x_quadrupled = POSIX::ldexp($x, 2);

=item C<ldiv>

(For computing dividends of long integers.)
C<ldiv()> is C-specific, use C</> and C<int()> instead.

=item C<link>

This is identical to Perl's builtin C<link()> function
for creating hard links into files, see L<perlfunc/link>.

=item C<localeconv>

Get numeric formatting information.  Returns a reference to a hash
containing the current locale formatting values.  Users of this function
should also read L<perllocale>, which provides a comprehensive
discussion of Perl locale handling, including
L<a section devoted to this function|perllocale/The localeconv function>.

Here is how to query the database for the B<de> (Deutsch or German) locale.

	my $loc = POSIX::setlocale( &POSIX::LC_ALL, "de" );
	print "Locale: \"$loc\"\n";
	my $lconv = POSIX::localeconv();
	foreach my $property (qw(
		decimal_point
		thousands_sep
		grouping
		int_curr_symbol
		currency_symbol
		mon_decimal_point
		mon_thousands_sep
		mon_grouping
		positive_sign
		negative_sign
		int_frac_digits
		frac_digits
		p_cs_precedes
		p_sep_by_space
		n_cs_precedes
		n_sep_by_space
		p_sign_posn
		n_sign_posn
	))
	{
		printf qq(%s: "%s",\n),
			$property, $lconv->{$property};
	}

=item C<localtime>

This is identical to Perl's builtin C<localtime()> function for
converting seconds since the epoch to a date see L<perlfunc/localtime>.

=item C<log>

This is identical to Perl's builtin C<log()> function,
returning the natural (I<e>-based) logarithm of the numerical argument,
see L<perlfunc/log>.

=item C<log10>

This is identical to the C function C<log10()>,
returning the 10-base logarithm of the numerical argument.
You can also use

    sub log10 { log($_[0]) / log(10) }

or

    sub log10 { log($_[0]) / 2.30258509299405 }

or

    sub log10 { log($_[0]) * 0.434294481903252 }

=item C<longjmp>

C<longjmp()> is C-specific: use L<perlfunc/die> instead.

=item C<lseek>

Move the file's read/write position.  This uses file descriptors such as
those obtained by calling C<POSIX::open>.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	$off_t = POSIX::lseek( $fd, 0, &POSIX::SEEK_SET );

Returns C<undef> on failure.

=item C<malloc>

C<malloc()> is C-specific.  Perl does memory management transparently.

=item C<mblen>

This is identical to the C function C<mblen()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather
useless function.

=item C<mbstowcs>

This is identical to the C function C<mbstowcs()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather
useless function.

=item C<mbtowc>

This is identical to the C function C<mbtowc()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather
useless function.

=item C<memchr>

C<memchr()> is C-specific, see L<perlfunc/index> instead.

=item C<memcmp>

C<memcmp()> is C-specific, use C<eq> instead, see L<perlop>.

=item C<memcpy>

C<memcpy()> is C-specific, use C<=>, see L<perlop>, or see L<perlfunc/substr>.

=item C<memmove>

C<memmove()> is C-specific, use C<=>, see L<perlop>, or see L<perlfunc/substr>.

=item C<memset>

C<memset()> is C-specific, use C<x> instead, see L<perlop>.

=item C<mkdir>

This is identical to Perl's builtin C<mkdir()> function
for creating directories, see L<perlfunc/mkdir>.

=item C<mkfifo>

This is similar to the C function C<mkfifo()> for creating
FIFO special files.

	if (mkfifo($path, $mode)) { ....

Returns C<undef> on failure.  The C<$mode> is similar to the
mode of C<mkdir()>, see L<perlfunc/mkdir>, though for C<mkfifo>
you B<must> specify the C<$mode>.

=item C<mktime>

Convert date/time info to a calendar time.

Synopsis:

	mktime(sec, min, hour, mday, mon, year, wday = 0,
	       yday = 0, isdst = -1)

The month (C<mon>), weekday (C<wday>), and yearday (C<yday>) begin at zero.
I.e. January is 0, not 1; Sunday is 0, not 1; January 1st is 0, not 1.  The
year (C<year>) is given in years since 1900.  I.e. The year 1995 is 95; the
year 2001 is 101.  Consult your system's C<mktime()> manpage for details
about these and the other arguments.

Calendar time for December 12, 1995, at 10:30 am.

	$time_t = POSIX::mktime( 0, 30, 10, 12, 11, 95 );
	print "Date = ", POSIX::ctime($time_t);

Returns C<undef> on failure.

=item C<modf>

Return the integral and fractional parts of a floating-point number.

	($fractional, $integral) = POSIX::modf( 3.14 );

=item C<nice>

This is similar to the C function C<nice()>, for changing
the scheduling preference of the current process.  Positive
arguments mean more polite process, negative values more
needy process.  Normal user processes can only be more polite.

Returns C<undef> on failure.

=item C<offsetof>

C<offsetof()> is C-specific, you probably want to see L<perlfunc/pack> instead.

=item C<open>

Open a file for reading for writing.  This returns file descriptors, not
Perl filehandles.  Use C<POSIX::close> to close the file.

Open a file read-only with mode 0666.

	$fd = POSIX::open( "foo" );

Open a file for read and write.

	$fd = POSIX::open( "foo", &POSIX::O_RDWR );

Open a file for write, with truncation.

	$fd = POSIX::open(
		"foo", &POSIX::O_WRONLY | &POSIX::O_TRUNC
	);

Create a new file with mode 0640.  Set up the file for writing.

	$fd = POSIX::open(
		"foo", &POSIX::O_CREAT | &POSIX::O_WRONLY, 0640
	);

Returns C<undef> on failure.

See also L<perlfunc/sysopen>.

=item C<opendir>

Open a directory for reading.

	$dir = POSIX::opendir( "/var" );
	@files = POSIX::readdir( $dir );
	POSIX::closedir( $dir );

Returns C<undef> on failure.

=item C<pathconf>

Retrieves the value of a configurable limit on a file or directory.

The following will determine the maximum length of the longest allowable
pathname on the filesystem which holds C</var>.

	$path_max = POSIX::pathconf( "/var",
				      &POSIX::_PC_PATH_MAX );

Returns C<undef> on failure.

=item C<pause>

This is similar to the C function C<pause()>, which suspends
the execution of the current process until a signal is received.

Returns C<undef> on failure.

=item C<perror>

This is identical to the C function C<perror()>, which outputs to the
standard error stream the specified message followed by C<": "> and the
current error string.  Use the C<warn()> function and the C<$!>
variable instead, see L<perlfunc/warn> and L<perlvar/$ERRNO>.

=item C<pipe>

Create an interprocess channel.  This returns file descriptors like those
returned by C<POSIX::open>.

	my ($read, $write) = POSIX::pipe();
	POSIX::write( $write, "hello", 5 );
	POSIX::read( $read, $buf, 5 );

See also L<perlfunc/pipe>.

=item C<pow>

Computes C<$x> raised to the power C<$exponent>.

	$ret = POSIX::pow( $x, $exponent );

You can also use the C<**> operator, see L<perlop>.

=item C<printf>

Formats and prints the specified arguments to STDOUT.
See also L<perlfunc/printf>.

=item C<putc>

C<putc()> is C-specific, see L<perlfunc/print> instead.

=item C<putchar>

C<putchar()> is C-specific, see L<perlfunc/print> instead.

=item C<puts>

C<puts()> is C-specific, see L<perlfunc/print> instead.

=item C<qsort>

C<qsort()> is C-specific, see L<perlfunc/sort> instead.

=item C<raise>

Sends the specified signal to the current process.
See also L<perlfunc/kill> and the C<$$> in L<perlvar/$PID>.

=item C<rand>

C<rand()> is non-portable, see L<perlfunc/rand> instead.

=item C<read>

Read from a file.  This uses file descriptors such as those obtained by
calling C<POSIX::open>.  If the buffer C<$buf> is not large enough for the
read then Perl will extend it to make room for the request.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	$bytes = POSIX::read( $fd, $buf, 3 );

Returns C<undef> on failure.

See also L<perlfunc/sysread>.

=item C<readdir>

This is identical to Perl's builtin C<readdir()> function
for reading directory entries, see L<perlfunc/readdir>.

=item C<realloc>

C<realloc()> is C-specific.  Perl does memory management transparently.

=item C<remove>

This is identical to Perl's builtin C<unlink()> function
for removing files, see L<perlfunc/unlink>.

=item C<rename>

This is identical to Perl's builtin C<rename()> function
for renaming files, see L<perlfunc/rename>.

=item C<rewind>

Seeks to the beginning of the file.

=item C<rewinddir>

This is identical to Perl's builtin C<rewinddir()> function for
rewinding directory entry streams, see L<perlfunc/rewinddir>.

=item C<rmdir>

This is identical to Perl's builtin C<rmdir()> function
for removing (empty) directories, see L<perlfunc/rmdir>.

=item C<scanf>

C<scanf()> is C-specific, use E<lt>E<gt> and regular expressions instead,
see L<perlre>.

=item C<setgid>

Sets the real group identifier and the effective group identifier for
this process.  Similar to assigning a value to the Perl's builtin
C<$)> variable, see L<perlvar/$EGID>, except that the latter
will change only the real user identifier, and that the setgid()
uses only a single numeric argument, as opposed to a space-separated
list of numbers.

=item C<setjmp>

C<setjmp()> is C-specific: use C<eval {}> instead,
see L<perlfunc/eval>.

=item C<setlocale>

Modifies and queries the program's underlying locale.  Users of this
function should read L<perllocale>, whch provides a comprehensive
discussion of Perl locale handling, knowledge of which is necessary to
properly use this function.  It contains
L<a section devoted to this function|perllocale/The setlocale function>.
The discussion here is merely a summary reference for C<setlocale()>.
Note that Perl itself is almost entirely unaffected by the locale
except within the scope of S<C<"use locale">>.  (Exceptions are listed
in L<perllocale/Not within the scope of any "use locale" variant>.)

The following examples assume

	use POSIX qw(setlocale LC_ALL LC_CTYPE);

has been issued.

The following will set the traditional UNIX system locale behavior
(the second argument C<"C">).

	$loc = setlocale( LC_ALL, "C" );

The following will query the current C<LC_CTYPE> category.  (No second
argument means 'query'.)

	$loc = setlocale( LC_CTYPE );

The following will set the C<LC_CTYPE> behaviour according to the locale
environment variables (the second argument C<"">).
Please see your system's C<setlocale(3)> documentation for the locale
environment variables' meaning or consult L<perllocale>.

	$loc = setlocale( LC_CTYPE, "" );

The following will set the C<LC_COLLATE> behaviour to Argentinian
Spanish. B<NOTE>: The naming and availability of locales depends on
your operating system. Please consult L<perllocale> for how to find
out which locales are available in your system.

	$loc = setlocale( LC_COLLATE, "es_AR.ISO8859-1" );

=item C<setpgid>

This is similar to the C function C<setpgid()> for
setting the process group identifier of the current process.

Returns C<undef> on failure.

=item C<setsid>

This is identical to the C function C<setsid()> for
setting the session identifier of the current process.

=item C<setuid>

Sets the real user identifier and the effective user identifier for
this process.  Similar to assigning a value to the Perl's builtin
C<$E<lt>> variable, see L<perlvar/$UID>, except that the latter
will change only the real user identifier.

=item C<sigaction>

Detailed signal management.  This uses C<POSIX::SigAction> objects for
the C<action> and C<oldaction> arguments (the oldaction can also be
just a hash reference).  Consult your system's C<sigaction> manpage
for details, see also C<POSIX::SigRt>.

Synopsis:

	sigaction(signal, action, oldaction = 0)

Returns C<undef> on failure.  The C<signal> must be a number (like
C<SIGHUP>), not a string (like C<"SIGHUP">), though Perl does try hard
to understand you.

If you use the C<SA_SIGINFO> flag, the signal handler will in addition to
the first argument, the signal name, also receive a second argument, a
hash reference, inside which are the following keys with the following
semantics, as defined by POSIX/SUSv3:

    signo       the signal number
    errno       the error number
    code        if this is zero or less, the signal was sent by
                a user process and the uid and pid make sense,
                otherwise the signal was sent by the kernel

The following are also defined by POSIX/SUSv3, but unfortunately
not very widely implemented:

    pid         the process id generating the signal
    uid         the uid of the process id generating the signal
    status      exit value or signal for SIGCHLD
    band        band event for SIGPOLL

A third argument is also passed to the handler, which contains a copy
of the raw binary contents of the C<siginfo> structure: if a system has
some non-POSIX fields, this third argument is where to C<unpack()> them
from.

Note that not all C<siginfo> values make sense simultaneously (some are
valid only for certain signals, for example), and not all values make
sense from Perl perspective, you should to consult your system's
C<sigaction> and possibly also C<siginfo> documentation.

=item C<siglongjmp>

C<siglongjmp()> is C-specific: use L<perlfunc/die> instead.

=item C<sigpending>

Examine signals that are blocked and pending.  This uses C<POSIX::SigSet>
objects for the C<sigset> argument.  Consult your system's C<sigpending>
manpage for details.

Synopsis:

	sigpending(sigset)

Returns C<undef> on failure.

=item C<sigprocmask>

Change and/or examine calling process's signal mask.  This uses
C<POSIX::SigSet> objects for the C<sigset> and C<oldsigset> arguments.
Consult your system's C<sigprocmask> manpage for details.

Synopsis:

	sigprocmask(how, sigset, oldsigset = 0)

Returns C<undef> on failure.

Note that you can't reliably block or unblock a signal from its own signal
handler if you're using safe signals. Other signals can be blocked or unblocked
reliably.

=item C<sigsetjmp>

C<sigsetjmp()> is C-specific: use C<eval {}> instead,
see L<perlfunc/eval>.

=item C<sigsuspend>

Install a signal mask and suspend process until signal arrives.  This uses
C<POSIX::SigSet> objects for the C<signal_mask> argument.  Consult your
system's C<sigsuspend> manpage for details.

Synopsis:

	sigsuspend(signal_mask)

Returns C<undef> on failure.

=item C<sin>

This is identical to Perl's builtin C<sin()> function
for returning the sine of the numerical argument,
see L<perlfunc/sin>.  See also L<Math::Trig>.

=item C<sinh>

This is identical to the C function C<sinh()>
for returning the hyperbolic sine of the numerical argument.
See also L<Math::Trig>.

=item C<sleep>

This is functionally identical to Perl's builtin C<sleep()> function
for suspending the execution of the current for process for certain
number of seconds, see L<perlfunc/sleep>.  There is one significant
difference, however: C<POSIX::sleep()> returns the number of
B<unslept> seconds, while the C<CORE::sleep()> returns the
number of slept seconds.

=item C<sprintf>

This is similar to Perl's builtin C<sprintf()> function
for returning a string that has the arguments formatted as requested,
see L<perlfunc/sprintf>.

=item C<sqrt>

This is identical to Perl's builtin C<sqrt()> function.
for returning the square root of the numerical argument,
see L<perlfunc/sqrt>.

=item C<srand>

Give a seed the pseudorandom number generator, see L<perlfunc/srand>.

=item C<sscanf>

C<sscanf()> is C-specific, use regular expressions instead,
see L<perlre>.

=item C<stat>

This is identical to Perl's builtin C<stat()> function
for returning information about files and directories.

=item C<strcat>

C<strcat()> is C-specific, use C<.=> instead, see L<perlop>.

=item C<strchr>

C<strchr()> is C-specific, see L<perlfunc/index> instead.

=item C<strcmp>

C<strcmp()> is C-specific, use C<eq> or C<cmp> instead, see L<perlop>.

=item C<strcoll>

This is identical to the C function C<strcoll()>
for collating (comparing) strings transformed using
the C<strxfrm()> function.  Not really needed since
Perl can do this transparently, see L<perllocale>.

=item C<strcpy>

C<strcpy()> is C-specific, use C<=> instead, see L<perlop>.

=item C<strcspn>

C<strcspn()> is C-specific, use regular expressions instead,
see L<perlre>.

=item C<strerror>

Returns the error string for the specified errno.
Identical to the string form of the C<$!>, see L<perlvar/$ERRNO>.

=item C<strftime>

Convert date and time information to string.  Returns the string.

Synopsis:

	strftime(fmt, sec, min, hour, mday, mon, year,
		 wday = -1, yday = -1, isdst = -1)

The month (C<mon>), weekday (C<wday>), and yearday (C<yday>) begin at zero.
I.e. January is 0, not 1; Sunday is 0, not 1; January 1st is 0, not 1.  The
year (C<year>) is given in years since 1900.  I.e., the year 1995 is 95; the
year 2001 is 101.  Consult your system's C<strftime()> manpage for details
about these and the other arguments.

If you want your code to be portable, your format (C<fmt>) argument
should use only the conversion specifiers defined by the ANSI C
standard (C89, to play safe).  These are C<aAbBcdHIjmMpSUwWxXyYZ%>.
But even then, the B<results> of some of the conversion specifiers are
non-portable.  For example, the specifiers C<aAbBcpZ> change according
to the locale settings of the user, and both how to set locales (the
locale names) and what output to expect are non-standard.
The specifier C<c> changes according to the timezone settings of the
user and the timezone computation rules of the operating system.
The C<Z> specifier is notoriously unportable since the names of
timezones are non-standard. Sticking to the numeric specifiers is the
safest route.

The given arguments are made consistent as though by calling
C<mktime()> before calling your system's C<strftime()> function,
except that the C<isdst> value is not affected.

The string for Tuesday, December 12, 1995.

	$str = POSIX::strftime( "%A, %B %d, %Y",
				 0, 0, 0, 12, 11, 95, 2 );
	print "$str\n";

=item C<strlen>

C<strlen()> is C-specific, use C<length()> instead, see L<perlfunc/length>.

=item C<strncat>

C<strncat()> is C-specific, use C<.=> instead, see L<perlop>.

=item C<strncmp>

C<strncmp()> is C-specific, use C<eq> instead, see L<perlop>.

=item C<strncpy>

C<strncpy()> is C-specific, use C<=> instead, see L<perlop>.

=item C<strpbrk>

C<strpbrk()> is C-specific, use regular expressions instead,
see L<perlre>.

=item C<strrchr>

C<strrchr()> is C-specific, see L<perlfunc/rindex> instead.

=item C<strspn>

C<strspn()> is C-specific, use regular expressions instead,
see L<perlre>.

=item C<strstr>

This is identical to Perl's builtin C<index()> function,
see L<perlfunc/index>.

=item C<strtod>

String to double translation. Returns the parsed number and the number
of characters in the unparsed portion of the string.  Truly
POSIX-compliant systems set C<$!> (C<$ERRNO>) to indicate a translation
error, so clear C<$!> before calling strtod.  However, non-POSIX systems
may not check for overflow, and therefore will never set C<$!>.

strtod respects any POSIX I<setlocale()> C<LC_TIME> settings,
regardless of whether or not it is called from Perl code that is within
the scope of S<C<use locale>>.

To parse a string C<$str> as a floating point number use

    $! = 0;
    ($num, $n_unparsed) = POSIX::strtod($str);

The second returned item and C<$!> can be used to check for valid input:

    if (($str eq '') || ($n_unparsed != 0) || $!) {
        die "Non-numeric input $str" . ($! ? ": $!\n" : "\n");
    }

When called in a scalar context strtod returns the parsed number.

=item C<strtok>

C<strtok()> is C-specific, use regular expressions instead, see
L<perlre>, or L<perlfunc/split>.

=item C<strtol>

String to (long) integer translation.  Returns the parsed number and
the number of characters in the unparsed portion of the string.  Truly
POSIX-compliant systems set C<$!> (C<$ERRNO>) to indicate a translation
error, so clear C<$!> before calling C<strtol>.  However, non-POSIX systems
may not check for overflow, and therefore will never set C<$!>.

C<strtol> should respect any POSIX I<setlocale()> settings.

To parse a string C<$str> as a number in some base C<$base> use

    $! = 0;
    ($num, $n_unparsed) = POSIX::strtol($str, $base);

The base should be zero or between 2 and 36, inclusive.  When the base
is zero or omitted strtol will use the string itself to determine the
base: a leading "0x" or "0X" means hexadecimal; a leading "0" means
octal; any other leading characters mean decimal.  Thus, "1234" is
parsed as a decimal number, "01234" as an octal number, and "0x1234"
as a hexadecimal number.

The second returned item and C<$!> can be used to check for valid input:

    if (($str eq '') || ($n_unparsed != 0) || !$!) {
        die "Non-numeric input $str" . $! ? ": $!\n" : "\n";
    }

When called in a scalar context strtol returns the parsed number.

=item C<strtoul>

String to unsigned (long) integer translation.  C<strtoul()> is identical
to C<strtol()> except that C<strtoul()> only parses unsigned integers.  See
L</strtol> for details.

Note: Some vendors supply C<strtod()> and C<strtol()> but not C<strtoul()>.
Other vendors that do supply C<strtoul()> parse "-1" as a valid value.

=item C<strxfrm>

String transformation.  Returns the transformed string.

	$dst = POSIX::strxfrm( $src );

Used in conjunction with the C<strcoll()> function, see L</strcoll>.

Not really needed since Perl can do this transparently, see
L<perllocale>.

=item C<sysconf>

Retrieves values of system configurable variables.

The following will get the machine's clock speed.

	$clock_ticks = POSIX::sysconf( &POSIX::_SC_CLK_TCK );

Returns C<undef> on failure.

=item C<system>

This is identical to Perl's builtin C<system()> function, see
L<perlfunc/system>.

=item C<tan>

This is identical to the C function C<tan()>, returning the
tangent of the numerical argument.  See also L<Math::Trig>.

=item C<tanh>

This is identical to the C function C<tanh()>, returning the
hyperbolic tangent of the numerical argument.   See also L<Math::Trig>.

=item C<tcdrain>

This is similar to the C function C<tcdrain()> for draining
the output queue of its argument stream.

Returns C<undef> on failure.

=item C<tcflow>

This is similar to the C function C<tcflow()> for controlling
the flow of its argument stream.

Returns C<undef> on failure.

=item C<tcflush>

This is similar to the C function C<tcflush()> for flushing
the I/O buffers of its argument stream.

Returns C<undef> on failure.

=item C<tcgetpgrp>

This is identical to the C function C<tcgetpgrp()> for returning the
process group identifier of the foreground process group of the controlling
terminal.

=item C<tcsendbreak>

This is similar to the C function C<tcsendbreak()> for sending
a break on its argument stream.

Returns C<undef> on failure.

=item C<tcsetpgrp>

This is similar to the C function C<tcsetpgrp()> for setting the
process group identifier of the foreground process group of the controlling
terminal.

Returns C<undef> on failure.

=item C<time>

This is identical to Perl's builtin C<time()> function
for returning the number of seconds since the epoch
(whatever it is for the system), see L<perlfunc/time>.

=item C<times>

The C<times()> function returns elapsed realtime since some point in the past
(such as system startup), user and system times for this process, and user
and system times used by child processes.  All times are returned in clock
ticks.

    ($realtime, $user, $system, $cuser, $csystem) 
	= POSIX::times();

Note: Perl's builtin C<times()> function returns four values, measured in
seconds.

=item C<tmpfile>

Use method C<IO::File::new_tmpfile()> instead, or see L<File::Temp>.

=item C<tmpnam>

Returns a name for a temporary file.

	$tmpfile = POSIX::tmpnam();

For security reasons, which are probably detailed in your system's
documentation for the C library C<tmpnam()> function, this interface
should not be used; instead see L<File::Temp>.

=item C<tolower>

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using the C<lc()> function,
see L<perlfunc/lc>, or the equivalent C<\L> operator inside doublequotish
strings.

=item C<toupper>

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using the C<uc()> function,
see L<perlfunc/uc>, or the equivalent C<\U> operator inside doublequotish
strings.

=item C<ttyname>

This is identical to the C function C<ttyname()> for returning the
name of the current terminal.

=item C<tzname>

Retrieves the time conversion information from the C<tzname> variable.

	POSIX::tzset();
	($std, $dst) = POSIX::tzname();

=item C<tzset>

This is identical to the C function C<tzset()> for setting
the current timezone based on the environment variable C<TZ>,
to be used by C<ctime()>, C<localtime()>, C<mktime()>, and C<strftime()>
functions.

=item C<umask>

This is identical to Perl's builtin C<umask()> function
for setting (and querying) the file creation permission mask,
see L<perlfunc/umask>.

=item C<uname>

Get name of current operating system.

	($sysname, $nodename, $release, $version, $machine)
		= POSIX::uname();

Note that the actual meanings of the various fields are not
that well standardized, do not expect any great portability.
The C<$sysname> might be the name of the operating system,
the C<$nodename> might be the name of the host, the C<$release>
might be the (major) release number of the operating system,
the C<$version> might be the (minor) release number of the
operating system, and the C<$machine> might be a hardware identifier.
Maybe.

=item C<ungetc>

Use method C<IO::Handle::ungetc()> instead.

=item C<unlink>

This is identical to Perl's builtin C<unlink()> function
for removing files, see L<perlfunc/unlink>.

=item C<utime>

This is identical to Perl's builtin C<utime()> function
for changing the time stamps of files and directories,
see L<perlfunc/utime>.

=item C<vfprintf>

C<vfprintf()> is C-specific, see L<perlfunc/printf> instead.

=item C<vprintf>

C<vprintf()> is C-specific, see L<perlfunc/printf> instead.

=item C<vsprintf>

C<vsprintf()> is C-specific, see L<perlfunc/sprintf> instead.

=item C<wait>

This is identical to Perl's builtin C<wait()> function,
see L<perlfunc/wait>.

=item C<waitpid>

Wait for a child process to change state.  This is identical to Perl's
builtin C<waitpid()> function, see L<perlfunc/waitpid>.

	$pid = POSIX::waitpid( -1, POSIX::WNOHANG );
	print "status = ", ($? / 256), "\n";

=item C<wcstombs>

This is identical to the C function C<wcstombs()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather
useless function.

=item C<wctomb>

This is identical to the C function C<wctomb()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather
useless function.

=item C<write>

Write to a file.  This uses file descriptors such as those obtained by
calling C<POSIX::open>.

	$fd = POSIX::open( "foo", &POSIX::O_WRONLY );
	$buf = "hello";
	$bytes = POSIX::write( $fd, $buf, 5 );

Returns C<undef> on failure.

See also L<perlfunc/syswrite>.

=back

=head1 CLASSES

=head2 C<POSIX::SigAction>

=over 8

=item C<new>

Creates a new C<POSIX::SigAction> object which corresponds to the C
C<struct sigaction>.  This object will be destroyed automatically when
it is no longer needed.  The first parameter is the handler, a sub
reference.  The second parameter is a C<POSIX::SigSet> object, it
defaults to the empty set.  The third parameter contains the
C<sa_flags>, it defaults to 0.

	$sigset = POSIX::SigSet->new(SIGINT, SIGQUIT);
	$sigaction = POSIX::SigAction->new(
			\&handler, $sigset, &POSIX::SA_NOCLDSTOP
		     );

This C<POSIX::SigAction> object is intended for use with the C<POSIX::sigaction()>
function.

=back

=over 8

=item C<handler>

=item C<mask>

=item C<flags>

accessor functions to get/set the values of a SigAction object.

	$sigset = $sigaction->mask;
	$sigaction->flags(&POSIX::SA_RESTART);

=item C<safe>

accessor function for the "safe signals" flag of a SigAction object; see
L<perlipc> for general information on safe (a.k.a. "deferred") signals.  If
you wish to handle a signal safely, use this accessor to set the "safe" flag
in the C<POSIX::SigAction> object:

	$sigaction->safe(1);

You may also examine the "safe" flag on the output action object which is
filled in when given as the third parameter to C<POSIX::sigaction()>:

	sigaction(SIGINT, $new_action, $old_action);
	if ($old_action->safe) {
	    # previous SIGINT handler used safe signals
	}

=back

=head2 C<POSIX::SigRt>

=over 8

=item C<%SIGRT>

A hash of the POSIX realtime signal handlers.  It is an extension of
the standard C<%SIG>, the C<$POSIX::SIGRT{SIGRTMIN}> is roughly equivalent
to C<$SIG{SIGRTMIN}>, but the right POSIX moves (see below) are made with
the C<POSIX::SigSet> and C<POSIX::sigaction> instead of accessing the C<%SIG>.

You can set the C<%POSIX::SIGRT> elements to set the POSIX realtime
signal handlers, use C<delete> and C<exists> on the elements, and use
C<scalar> on the C<%POSIX::SIGRT> to find out how many POSIX realtime
signals there are available S<C<(SIGRTMAX - SIGRTMIN + 1>>, the C<SIGRTMAX> is
a valid POSIX realtime signal).

Setting the C<%SIGRT> elements is equivalent to calling this:

  sub new {
    my ($rtsig, $handler, $flags) = @_;
    my $sigset = POSIX::SigSet($rtsig);
    my $sigact = POSIX::SigAction->new($handler,$sigset,$flags);
    sigaction($rtsig, $sigact);
  }

The flags default to zero, if you want something different you can
either use C<local> on C<$POSIX::SigRt::SIGACTION_FLAGS>, or you can
derive from POSIX::SigRt and define your own C<new()> (the tied hash
STORE method of the C<%SIGRT> calls C<new($rtsig, $handler, $SIGACTION_FLAGS)>,
where the C<$rtsig> ranges from zero to S<C<SIGRTMAX - SIGRTMIN + 1)>>.

Just as with any signal, you can use C<sigaction($rtsig, undef, $oa)> to
retrieve the installed signal handler (or, rather, the signal action).

B<NOTE:> whether POSIX realtime signals really work in your system, or
whether Perl has been compiled so that it works with them, is outside
of this discussion.

=item C<SIGRTMIN>

Return the minimum POSIX realtime signal number available, or C<undef>
if no POSIX realtime signals are available.

=item C<SIGRTMAX>

Return the maximum POSIX realtime signal number available, or C<undef>
if no POSIX realtime signals are available.

=back

=head2 C<POSIX::SigSet>

=over 8

=item C<new>

Create a new SigSet object.  This object will be destroyed automatically
when it is no longer needed.  Arguments may be supplied to initialize the
set.

Create an empty set.

	$sigset = POSIX::SigSet->new;

Create a set with C<SIGUSR1>.

	$sigset = POSIX::SigSet->new( &POSIX::SIGUSR1 );

=item C<addset>

Add a signal to a SigSet object.

	$sigset->addset( &POSIX::SIGUSR2 );

Returns C<undef> on failure.

=item C<delset>

Remove a signal from the SigSet object.

	$sigset->delset( &POSIX::SIGUSR2 );

Returns C<undef> on failure.

=item C<emptyset>

Initialize the SigSet object to be empty.

	$sigset->emptyset();

Returns C<undef> on failure.

=item C<fillset>

Initialize the SigSet object to include all signals.

	$sigset->fillset();

Returns C<undef> on failure.

=item C<ismember>

Tests the SigSet object to see if it contains a specific signal.

	if( $sigset->ismember( &POSIX::SIGUSR1 ) ){
		print "contains SIGUSR1\n";
	}

=back

=head2 C<POSIX::Termios>

=over 8

=item C<new>

Create a new Termios object.  This object will be destroyed automatically
when it is no longer needed.  A Termios object corresponds to the termios
C struct.  C<new()> mallocs a new one, C<getattr()> fills it from a file descriptor,
and C<setattr()> sets a file descriptor's parameters to match Termios' contents.

	$termios = POSIX::Termios->new;

=item C<getattr>

Get terminal control attributes.

Obtain the attributes for stdin.

	$termios->getattr( 0 ) # Recommended for clarity.
	$termios->getattr()

Obtain the attributes for stdout.

	$termios->getattr( 1 )

Returns C<undef> on failure.

=item C<getcc>

Retrieve a value from the c_cc field of a termios object.  The c_cc field is
an array so an index must be specified.

	$c_cc[1] = $termios->getcc(1);

=item C<getcflag>

Retrieve the c_cflag field of a termios object.

	$c_cflag = $termios->getcflag;

=item C<getiflag>

Retrieve the c_iflag field of a termios object.

	$c_iflag = $termios->getiflag;

=item C<getispeed>

Retrieve the input baud rate.

	$ispeed = $termios->getispeed;

=item C<getlflag>

Retrieve the c_lflag field of a termios object.

	$c_lflag = $termios->getlflag;

=item C<getoflag>

Retrieve the c_oflag field of a termios object.

	$c_oflag = $termios->getoflag;

=item C<getospeed>

Retrieve the output baud rate.

	$ospeed = $termios->getospeed;

=item C<setattr>

Set terminal control attributes.

Set attributes immediately for stdout.

	$termios->setattr( 1, &POSIX::TCSANOW );

Returns C<undef> on failure.

=item C<setcc>

Set a value in the c_cc field of a termios object.  The c_cc field is an
array so an index must be specified.

	$termios->setcc( &POSIX::VEOF, 1 );

=item C<setcflag>

Set the c_cflag field of a termios object.

	$termios->setcflag( $c_cflag | &POSIX::CLOCAL );

=item C<setiflag>

Set the c_iflag field of a termios object.

	$termios->setiflag( $c_iflag | &POSIX::BRKINT );

=item C<setispeed>

Set the input baud rate.

	$termios->setispeed( &POSIX::B9600 );

Returns C<undef> on failure.

=item C<setlflag>

Set the c_lflag field of a termios object.

	$termios->setlflag( $c_lflag | &POSIX::ECHO );

=item C<setoflag>

Set the c_oflag field of a termios object.

	$termios->setoflag( $c_oflag | &POSIX::OPOST );

=item C<setospeed>

Set the output baud rate.

	$termios->setospeed( &POSIX::B9600 );

Returns C<undef> on failure.

=item Baud rate values

C<B38400> C<B75> C<B200> C<B134> C<B300> C<B1800> C<B150> C<B0> C<B19200> C<B1200> C<B9600> C<B600> C<B4800> C<B50> C<B2400> C<B110>

=item Terminal interface values

C<TCSADRAIN> C<TCSANOW> C<TCOON> C<TCIOFLUSH> C<TCOFLUSH> C<TCION> C<TCIFLUSH> C<TCSAFLUSH> C<TCIOFF> C<TCOOFF>

=item C<c_cc> field values

C<VEOF> C<VEOL> C<VERASE> C<VINTR> C<VKILL> C<VQUIT> C<VSUSP> C<VSTART> C<VSTOP> C<VMIN> C<VTIME> C<NCCS>

=item C<c_cflag> field values

C<CLOCAL> C<CREAD> C<CSIZE> C<CS5> C<CS6> C<CS7> C<CS8> C<CSTOPB> C<HUPCL> C<PARENB> C<PARODD>

=item C<c_iflag> field values

C<BRKINT> C<ICRNL> C<IGNBRK> C<IGNCR> C<IGNPAR> C<INLCR> C<INPCK> C<ISTRIP> C<IXOFF> C<IXON> C<PARMRK>

=item C<c_lflag> field values

C<ECHO> C<ECHOE> C<ECHOK> C<ECHONL> C<ICANON> C<IEXTEN> C<ISIG> C<NOFLSH> C<TOSTOP>

=item C<c_oflag> field values

C<OPOST>

=back

=head1 PATHNAME CONSTANTS

=over 8

=item Constants

C<_PC_CHOWN_RESTRICTED> C<_PC_LINK_MAX> C<_PC_MAX_CANON> C<_PC_MAX_INPUT> C<_PC_NAME_MAX>
C<_PC_NO_TRUNC> C<_PC_PATH_MAX> C<_PC_PIPE_BUF> C<_PC_VDISABLE>

=back

=head1 POSIX CONSTANTS

=over 8

=item Constants

C<_POSIX_ARG_MAX> C<_POSIX_CHILD_MAX> C<_POSIX_CHOWN_RESTRICTED> C<_POSIX_JOB_CONTROL>
C<_POSIX_LINK_MAX> C<_POSIX_MAX_CANON> C<_POSIX_MAX_INPUT> C<_POSIX_NAME_MAX>
C<_POSIX_NGROUPS_MAX> C<_POSIX_NO_TRUNC> C<_POSIX_OPEN_MAX> C<_POSIX_PATH_MAX>
C<_POSIX_PIPE_BUF> C<_POSIX_SAVED_IDS> C<_POSIX_SSIZE_MAX> C<_POSIX_STREAM_MAX>
C<_POSIX_TZNAME_MAX> C<_POSIX_VDISABLE> C<_POSIX_VERSION>

=back

=head1 SYSTEM CONFIGURATION

=over 8

=item Constants

C<_SC_ARG_MAX> C<_SC_CHILD_MAX> C<_SC_CLK_TCK> C<_SC_JOB_CONTROL> C<_SC_NGROUPS_MAX>
C<_SC_OPEN_MAX> C<_SC_PAGESIZE> C<_SC_SAVED_IDS> C<_SC_STREAM_MAX> C<_SC_TZNAME_MAX>
C<_SC_VERSION>

=back

=head1 ERRNO

=over 8

=item Constants

C<E2BIG> C<EACCES> C<EADDRINUSE> C<EADDRNOTAVAIL> C<EAFNOSUPPORT> C<EAGAIN> C<EALREADY> C<EBADF> C<EBADMSG>
C<EBUSY> C<ECANCELED> C<ECHILD> C<ECONNABORTED> C<ECONNREFUSED> C<ECONNRESET> C<EDEADLK> C<EDESTADDRREQ>
C<EDOM> C<EDQUOT> C<EEXIST> C<EFAULT> C<EFBIG> C<EHOSTDOWN> C<EHOSTUNREACH> C<EIDRM> C<EILSEQ> C<EINPROGRESS>
C<EINTR> C<EINVAL> C<EIO> C<EISCONN> C<EISDIR> C<ELOOP> C<EMFILE> C<EMLINK> C<EMSGSIZE> C<ENAMETOOLONG>
C<ENETDOWN> C<ENETRESET> C<ENETUNREACH> C<ENFILE> C<ENOBUFS> C<ENODATA> C<ENODEV> C<ENOENT> C<ENOEXEC>
C<ENOLCK> C<ENOLINK> C<ENOMEM> C<ENOMSG> C<ENOPROTOOPT> C<ENOSPC> C<ENOSR> C<ENOSTR> C<ENOSYS> C<ENOTBLK>
C<ENOTCONN> C<ENOTDIR> C<ENOTEMPTY> C<ENOTRECOVERABLE> C<ENOTSOCK> C<ENOTSUP> C<ENOTTY> C<ENXIO>
C<EOPNOTSUPP> C<EOTHER> C<EOVERFLOW> C<EOWNERDEAD> C<EPERM> C<EPFNOSUPPORT> C<EPIPE> C<EPROCLIM> C<EPROTO>
C<EPROTONOSUPPORT> C<EPROTOTYPE> C<ERANGE> C<EREMOTE> C<ERESTART> C<EROFS> C<ESHUTDOWN>
C<ESOCKTNOSUPPORT> C<ESPIPE> C<ESRCH> C<ESTALE> C<ETIME> C<ETIMEDOUT> C<ETOOMANYREFS> C<ETXTBSY> C<EUSERS>
C<EWOULDBLOCK> C<EXDEV>

=back

=head1 FCNTL

=over 8

=item Constants

C<FD_CLOEXEC> C<F_DUPFD> C<F_GETFD> C<F_GETFL> C<F_GETLK> C<F_OK> C<F_RDLCK> C<F_SETFD> C<F_SETFL> C<F_SETLK>
C<F_SETLKW> C<F_UNLCK> C<F_WRLCK> C<O_ACCMODE> C<O_APPEND> C<O_CREAT> C<O_EXCL> C<O_NOCTTY> C<O_NONBLOCK>
C<O_RDONLY> C<O_RDWR> C<O_TRUNC> C<O_WRONLY>

=back

=head1 FLOAT

=over 8

=item Constants

C<DBL_DIG> C<DBL_EPSILON> C<DBL_MANT_DIG> C<DBL_MAX> C<DBL_MAX_10_EXP> C<DBL_MAX_EXP> C<DBL_MIN>
C<DBL_MIN_10_EXP> C<DBL_MIN_EXP> C<FLT_DIG> C<FLT_EPSILON> C<FLT_MANT_DIG> C<FLT_MAX>
C<FLT_MAX_10_EXP> C<FLT_MAX_EXP> C<FLT_MIN> C<FLT_MIN_10_EXP> C<FLT_MIN_EXP> C<FLT_RADIX>
C<FLT_ROUNDS> C<LDBL_DIG> C<LDBL_EPSILON> C<LDBL_MANT_DIG> C<LDBL_MAX> C<LDBL_MAX_10_EXP>
C<LDBL_MAX_EXP> C<LDBL_MIN> C<LDBL_MIN_10_EXP> C<LDBL_MIN_EXP>

=back

=head1 LIMITS

=over 8

=item Constants

C<ARG_MAX> C<CHAR_BIT> C<CHAR_MAX> C<CHAR_MIN> C<CHILD_MAX> C<INT_MAX> C<INT_MIN> C<LINK_MAX> C<LONG_MAX>
C<LONG_MIN> C<MAX_CANON> C<MAX_INPUT> C<MB_LEN_MAX> C<NAME_MAX> C<NGROUPS_MAX> C<OPEN_MAX> C<PATH_MAX>
C<PIPE_BUF> C<SCHAR_MAX> C<SCHAR_MIN> C<SHRT_MAX> C<SHRT_MIN> C<SSIZE_MAX> C<STREAM_MAX> C<TZNAME_MAX>
C<UCHAR_MAX> C<UINT_MAX> C<ULONG_MAX> C<USHRT_MAX>

=back

=head1 LOCALE

=over 8

=item Constants

C<LC_ALL> C<LC_COLLATE> C<LC_CTYPE> C<LC_MONETARY> C<LC_NUMERIC> C<LC_TIME>

=back

=head1 MATH

=over 8

=item Constants

C<HUGE_VAL>

=back

=head1 SIGNAL

=over 8

=item Constants

C<SA_NOCLDSTOP> C<SA_NOCLDWAIT> C<SA_NODEFER> C<SA_ONSTACK> C<SA_RESETHAND> C<SA_RESTART>
C<SA_SIGINFO> C<SIGABRT> C<SIGALRM> C<SIGCHLD> C<SIGCONT> C<SIGFPE> C<SIGHUP> C<SIGILL> C<SIGINT>
C<SIGKILL> C<SIGPIPE> C<SIGQUIT> C<SIGSEGV> C<SIGSTOP> C<SIGTERM> C<SIGTSTP> C<SIGTTIN> C<SIGTTOU>
C<SIGUSR1> C<SIGUSR2> C<SIG_BLOCK> C<SIG_DFL> C<SIG_ERR> C<SIG_IGN> C<SIG_SETMASK>
C<SIG_UNBLOCK>

=back

=head1 STAT

=over 8

=item Constants

C<S_IRGRP> C<S_IROTH> C<S_IRUSR> C<S_IRWXG> C<S_IRWXO> C<S_IRWXU> C<S_ISGID> C<S_ISUID> C<S_IWGRP> C<S_IWOTH>
C<S_IWUSR> C<S_IXGRP> C<S_IXOTH> C<S_IXUSR>

=item Macros

C<S_ISBLK> C<S_ISCHR> C<S_ISDIR> C<S_ISFIFO> C<S_ISREG>

=back

=head1 STDLIB

=over 8

=item Constants

C<EXIT_FAILURE> C<EXIT_SUCCESS> C<MB_CUR_MAX> C<RAND_MAX>

=back

=head1 STDIO

=over 8

=item Constants

C<BUFSIZ> C<EOF> C<FILENAME_MAX> C<L_ctermid> C<L_cuserid> C<L_tmpname> C<TMP_MAX>

=back

=head1 TIME

=over 8

=item Constants

C<CLK_TCK> C<CLOCKS_PER_SEC>

=back

=head1 UNISTD

=over 8

=item Constants

C<R_OK> C<SEEK_CUR> C<SEEK_END> C<SEEK_SET> C<STDIN_FILENO> C<STDOUT_FILENO> C<STDERR_FILENO> C<W_OK> C<X_OK>

=back

=head1 WAIT

=over 8

=item Constants

C<WNOHANG> C<WUNTRACED>

=over 16

=item C<WNOHANG>

Do not suspend the calling process until a child process
changes state but instead return immediately.

=item C<WUNTRACED>

Catch stopped child processes.

=back

=item Macros

C<WIFEXITED> C<WEXITSTATUS> C<WIFSIGNALED> C<WTERMSIG> C<WIFSTOPPED> C<WSTOPSIG>

=over 16

=item C<WIFEXITED>

C<WIFEXITED(${^CHILD_ERROR_NATIVE})> returns true if the child process
exited normally (C<exit()> or by falling off the end of C<main()>)

=item C<WEXITSTATUS>

C<WEXITSTATUS(${^CHILD_ERROR_NATIVE})> returns the normal exit status of
the child process (only meaningful if C<WIFEXITED(${^CHILD_ERROR_NATIVE})>
is true)

=item C<WIFSIGNALED>

C<WIFSIGNALED(${^CHILD_ERROR_NATIVE})> returns true if the child process
terminated because of a signal

=item C<WTERMSIG>

C<WTERMSIG(${^CHILD_ERROR_NATIVE})> returns the signal the child process
terminated for (only meaningful if
C<WIFSIGNALED(${^CHILD_ERROR_NATIVE})>
is true)

=item C<WIFSTOPPED>

C<WIFSTOPPED(${^CHILD_ERROR_NATIVE})> returns true if the child process is
currently stopped (can happen only if you specified the WUNTRACED flag
to C<waitpid()>)

=item C<WSTOPSIG>

C<WSTOPSIG(${^CHILD_ERROR_NATIVE})> returns the signal the child process
was stopped for (only meaningful if
C<WIFSTOPPED(${^CHILD_ERROR_NATIVE})>
is true)

=back

=back