posix.pod

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=item setsid

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

=item 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 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
SIGHUP), not a string (like "SIGHUP"), though Perl does try hard
to understand you.

If you use the 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 siginfo structure: if a system has
some non-POSIX fields, this third argument is where to unpack() them
from.

Note that not all 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 siglongjmp

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

=item 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 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.

=item sigsetjmp

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

=item 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 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 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 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 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 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 srand

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

=item sscanf

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

=item stat

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

=item strcat

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

=item strchr

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

=item strcmp

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

=item 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 strcpy

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

=item strcspn

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

=item strerror

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

=item 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 strlen

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

=item strncat

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

=item strncmp

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

=item strncpy

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

=item strpbrk

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

=item strrchr

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

=item strspn

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

=item strstr

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

=item 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 $! ($ERRNO) to indicate a translation
error, so clear $! before calling strtod.  However, non-POSIX systems
may not check for overflow, and therefore will never set $!.

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

To parse a string $str as a floating point number use

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

The second returned item and $! 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 strtok

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

=item 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 $! ($ERRNO) to indicate a translation
error, so clear $! before calling strtol.  However, non-POSIX systems
may not check for overflow, and therefore will never set $!.

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

To parse a string $str as a number in some base $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 $! 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 strtoul

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

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

=item 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 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 system

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

=item tan

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

=item tanh

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

=item 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 tcflow

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

Returns C<undef> on failure.

=item 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 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 tcsendbreak

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

Returns C<undef> on failure.

=item 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 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 times

The 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 tmpfile

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

=item 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 tmpnam() function, this interface
should not be used; instead see L<File::Temp>.

=item 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 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 ttyname

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

=item tzname

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

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

=item 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 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 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 ungetc

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

=item unlink

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

=item 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 vfprintf

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

=item vprintf

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

=item vsprintf

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

=item wait

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

=item 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 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 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 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( $b, $buf, 5 );

Returns C<undef> on failure.

See also L<perlfunc/syswrite>.

=back

=head1 CLASSES