=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 C<use
POSIX ()> and then use the fully qualified names (ie. C<POSIX::SEEK_END>),
or by giving an explicit import list.  If you do neither, and opt for the
default, 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 setjmp() call will elicit the
message "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 EDEADLK, or the semantics of the
errno values set by 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 ICANON macro after
all.  This could be construed to be a bug.

=head1 FUNCTIONS

=over 8

=item _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 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 abs

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

=item 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 acos

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

=item alarm

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

=item 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 asin

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

=item assert

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

=item atan

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

=item 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 atexit

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

=item atof

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 atoi

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 atol

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 bsearch

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

=item calloc

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

=item 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 chdir

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

=item chmod

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

=item 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 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 clock

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

=item 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 closedir

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

=item 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 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 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 ctermid

Generates the path name for the controlling terminal.

	$path = POSIX::ctermid();

=item ctime

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

=item cuserid

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

	$name = POSIX::cuserid();

=item 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 div

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

=item 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 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 errno

Returns the value of errno.

	$errno = POSIX::errno();

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

=item execl

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

=item execle

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

=item execlp

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

=item execv

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

=item execve

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

=item execvp

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

=item exit

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

=item 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 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 fclose

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

=item fcntl

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

=item fdopen

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

=item feof

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

=item ferror

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

=item fflush

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

=item fgetc

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

=item fgetpos

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

=item fgets

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

=item fileno

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

=item floor

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

=item 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 fopen

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

=item 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 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 C</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 fprintf

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

=item fputc

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

=item fputs

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

=item fread

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

=item free

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

=item freopen

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

=item frexp

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

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

=item fscanf

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

=item fseek

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

=item fsetpos

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

=item 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 fsync

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

=item ftell

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

=item fwrite

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

=item getc

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

=item getchar

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

=item getcwd

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

=item getegid

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

=item getenv

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

=item geteuid

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

=item getgid

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

=item getgrgid

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

=item getgrnam

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

=item getgroups

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

=item 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 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 getpid

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

=item 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 getpwnam

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

=item getpwuid

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

=item 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 getuid

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

=item 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 isalnum

This is identical to the C function, except that it can apply to a
single character or to a whole string.  Note that locale settings may
affect what characters are considered C<isalnum>.  Does not work on
Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:alnum:]]/> construct instead, or possibly
the C</\w/> construct.

=item isalpha

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<isalpha>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:alpha:]]/> construct instead.

=item 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 iscntrl

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<iscntrl>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:cntrl:]]/> construct instead.

=item isdigit

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<isdigit> (unlikely, but
still possible). Does not work on Unicode characters code point 256
or higher.  Consider using regular expressions and the C</[[:digit:]]/>
construct instead, or the C</\d/> construct.

=item isgraph

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<isgraph>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:graph:]]/> construct instead.

=item islower

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<islower>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:lower:]]/> construct instead.  Do B<not> use
C</[a-z]/>.

=item isprint

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<isprint>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:print:]]/> construct instead.

=item ispunct

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<ispunct>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:punct:]]/> construct instead.

=item isspace

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<isspace>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:space:]]/> construct instead, or the C</\s/>
construct.  (Note that C</\s/> and C</[[:space:]]/> are slightly
different in that C</[[:space:]]/> can normally match a vertical tab,
while C</\s/> does not.)

=item isupper

This is identical to the C function, except that it can apply to
a single character or to a whole string.  Note that locale settings
may affect what characters are considered C<isupper>.  Does not work
on Unicode characters code point 256 or higher.  Consider using regular
expressions and the C</[[:upper:]]/> construct instead.  Do B<not> use
C</[A-Z]/>.

=item isxdigit

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Note that locale settings may affect what
characters are considered C<isxdigit> (unlikely, but still possible).
Does not work on Unicode characters code point 256 or higher.
Consider using regular expressions and the C</[[:xdigit:]]/>
construct instead, or simply C</[0-9a-f]/i>.

=item 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 labs

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

=item 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 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 ldiv

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

=item link

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

=item localeconv

Get numeric formatting information.  Returns a reference to a hash
containing the current locale formatting values.

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

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

=item 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 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 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 longjmp

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

=item 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 malloc

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

=item 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 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 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 memchr

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

=item memcmp

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

=item memcpy

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

=item memmove

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

=item memset

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

=item mkdir

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

=item 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 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 modf

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

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

=item 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 offsetof

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

=item 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 opendir

Open a directory for reading.

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

Returns C<undef> on failure.

=item 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 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 perror

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

=item 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 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 printf

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

=item putc

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

=item putchar

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

=item puts

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

=item qsort

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

=item raise

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

=item rand

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

=item 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 readdir

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

=item realloc

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

=item remove

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

=item rename

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

=item rewind

Seeks to the beginning of the file.

=item rewinddir

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

=item rmdir

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

=item scanf

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

=item 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 setjmp

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

=item setlocale

Modifies and queries program's locale.  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 LC_CTYPE category.  (No second
argument means 'query'.)

	$loc = setlocale( LC_CTYPE );

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

	$loc = setlocale( LC_CTYPE, "" );

The following will set the 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 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 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.

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 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( $fd, $buf, 5 );

Returns C<undef> on failure.

See also L<perlfunc/syswrite>.

=back

=head1 CLASSES

=head2 POSIX::SigAction

=over 8

=item 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 handler

=item mask

=item flags

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

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

=item 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 POSIX::SigRt

=over 8

=item %SIGRT

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

You can set the %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 (SIGRTMAX - SIGRTMIN + 1, the SIGRTMAX is
a valid POSIX realtime signal).

Setting the %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 $POSIX::SigRt::SIGACTION_FLAGS, or you can
derive from POSIX::SigRt and define your own C<new()> (the tied hash
STORE method of the %SIGRT calls C<new($rtsig, $handler, $SIGACTION_FLAGS)>,
where the $rtsig ranges from zero to SIGRTMAX - SIGRTMIN + 1).

Just as with any signal, you can use 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 SIGRTMIN

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

=item SIGRTMAX

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

=back

=head2 POSIX::SigSet

=over 8

=item 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 SIGUSR1.

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

=item addset

Add a signal to a SigSet object.

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

Returns C<undef> on failure.

=item delset

Remove a signal from the SigSet object.

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

Returns C<undef> on failure.

=item emptyset

Initialize the SigSet object to be empty.

	$sigset->emptyset();

Returns C<undef> on failure.

=item fillset

Initialize the SigSet object to include all signals.

	$sigset->fillset();

Returns C<undef> on failure.

=item ismember

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

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

=back

=head2 POSIX::Termios

=over 8

=item 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.  new() mallocs a new one, getattr() fills it from a file descriptor,
and setattr() sets a file descriptor's parameters to match Termios' contents.

	$termios = POSIX::Termios->new;

=item 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 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 getcflag

Retrieve the c_cflag field of a termios object.

	$c_cflag = $termios->getcflag;

=item getiflag

Retrieve the c_iflag field of a termios object.

	$c_iflag = $termios->getiflag;

=item getispeed

Retrieve the input baud rate.

	$ispeed = $termios->getispeed;

=item getlflag

Retrieve the c_lflag field of a termios object.

	$c_lflag = $termios->getlflag;

=item getoflag

Retrieve the c_oflag field of a termios object.

	$c_oflag = $termios->getoflag;

=item getospeed

Retrieve the output baud rate.

	$ospeed = $termios->getospeed;

=item setattr

Set terminal control attributes.

Set attributes immediately for stdout.

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

Returns C<undef> on failure.

=item 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 setcflag

Set the c_cflag field of a termios object.

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

=item setiflag

Set the c_iflag field of a termios object.

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

=item setispeed

Set the input baud rate.

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

Returns C<undef> on failure.

=item setlflag

Set the c_lflag field of a termios object.

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

=item setoflag

Set the c_oflag field of a termios object.

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

=item setospeed

Set the output baud rate.

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

Returns C<undef> on failure.

=item Baud rate values

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

=item Terminal interface values

TCSADRAIN TCSANOW TCOON TCIOFLUSH TCOFLUSH TCION TCIFLUSH TCSAFLUSH TCIOFF TCOOFF

=item c_cc field values

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

=item c_cflag field values

CLOCAL CREAD CSIZE CS5 CS6 CS7 CS8 CSTOPB HUPCL PARENB PARODD

=item c_iflag field values

BRKINT ICRNL IGNBRK IGNCR IGNPAR INLCR INPCK ISTRIP IXOFF IXON PARMRK

=item c_lflag field values

ECHO ECHOE ECHOK ECHONL ICANON IEXTEN ISIG NOFLSH TOSTOP

=item c_oflag field values

OPOST

=back

=head1 PATHNAME CONSTANTS

=over 8

=item Constants

_PC_CHOWN_RESTRICTED _PC_LINK_MAX _PC_MAX_CANON _PC_MAX_INPUT _PC_NAME_MAX _PC_NO_TRUNC _PC_PATH_MAX _PC_PIPE_BUF _PC_VDISABLE

=back

=head1 POSIX CONSTANTS

=over 8

=item Constants

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

=back

=head1 SYSTEM CONFIGURATION

=over 8

=item Constants

_SC_ARG_MAX _SC_CHILD_MAX _SC_CLK_TCK _SC_JOB_CONTROL _SC_NGROUPS_MAX _SC_OPEN_MAX _SC_PAGESIZE _SC_SAVED_IDS _SC_STREAM_MAX _SC_TZNAME_MAX _SC_VERSION

=back

=head1 ERRNO

=over 8

=item Constants

E2BIG EACCES EADDRINUSE EADDRNOTAVAIL EAFNOSUPPORT EAGAIN EALREADY EBADF
EBUSY ECHILD ECONNABORTED ECONNREFUSED ECONNRESET EDEADLK EDESTADDRREQ
EDOM EDQUOT EEXIST EFAULT EFBIG EHOSTDOWN EHOSTUNREACH EINPROGRESS EINTR
EINVAL EIO EISCONN EISDIR ELOOP EMFILE EMLINK EMSGSIZE ENAMETOOLONG
ENETDOWN ENETRESET ENETUNREACH ENFILE ENOBUFS ENODEV ENOENT ENOEXEC
ENOLCK ENOMEM ENOPROTOOPT ENOSPC ENOSYS ENOTBLK ENOTCONN ENOTDIR
ENOTEMPTY ENOTSOCK ENOTTY ENXIO EOPNOTSUPP EPERM EPFNOSUPPORT EPIPE
EPROCLIM EPROTONOSUPPORT EPROTOTYPE ERANGE EREMOTE ERESTART EROFS
ESHUTDOWN ESOCKTNOSUPPORT ESPIPE ESRCH ESTALE ETIMEDOUT ETOOMANYREFS
ETXTBSY EUSERS EWOULDBLOCK EXDEV

=back

=head1 FCNTL

=over 8

=item Constants

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

=back

=head1 FLOAT

=over 8

=item Constants

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

=back

=head1 LIMITS

=over 8

=item Constants

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

=back

=head1 LOCALE

=over 8

=item Constants

LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME

=back

=head1 MATH

=over 8

=item Constants

HUGE_VAL

=back

=head1 SIGNAL

=over 8

=item Constants

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

=back

=head1 STAT

=over 8

=item Constants

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

=item Macros

S_ISBLK S_ISCHR S_ISDIR S_ISFIFO S_ISREG

=back

=head1 STDLIB

=over 8

=item Constants

EXIT_FAILURE EXIT_SUCCESS MB_CUR_MAX RAND_MAX

=back

=head1 STDIO

=over 8

=item Constants

BUFSIZ EOF FILENAME_MAX L_ctermid L_cuserid L_tmpname TMP_MAX

=back

=head1 TIME

=over 8

=item Constants

CLK_TCK CLOCKS_PER_SEC

=back

=head1 UNISTD

=over 8

=item Constants

R_OK SEEK_CUR SEEK_END SEEK_SET STDIN_FILENO STDOUT_FILENO STDERR_FILENO W_OK X_OK

=back

=head1 WAIT

=over 8

=item Constants

WNOHANG WUNTRACED

=over 16

=item WNOHANG

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

=item WUNTRACED

Catch stopped child processes.

=back

=item Macros

WIFEXITED WEXITSTATUS WIFSIGNALED WTERMSIG WIFSTOPPED WSTOPSIG

=over 16

=item WIFEXITED

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

=item WEXITSTATUS

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

=item WIFSIGNALED

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

=item WTERMSIG

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

=item WIFSTOPPED

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

=item WSTOPSIG

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

=back

=back