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POSIX

Perl 5 version 26.0 documentation

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POSIX

NAME
SYNOPSIS
DESCRIPTION
CAVEATS
FUNCTIONS
CLASSES
- POSIX::SigAction
- POSIX::SigRt
- POSIX::SigSet
- POSIX::Termios
PATHNAME CONSTANTS
POSIX CONSTANTS
SYSTEM CONFIGURATION
ERRNO
FCNTL
FLOAT
FLOATING-POINT ENVIRONMENT
LIMITS
LOCALE
MATH
SIGNAL
STAT
STDLIB
STDIO
TIME
UNISTD
WAIT
WINSOCK

NAME

POSIX - Perl interface to IEEE Std 1003.1

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

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.

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 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.

CAVEATS

Everything is exported by default (with a handful of exceptions). This is an unfortunate backwards compatibility feature and its use is strongly discouraged. You should either prevent the exporting (by saying use POSIX (); , as usual) and then use fully qualified names (e.g. POSIX::SEEK_END ), or give an explicit import list. If you do neither and opt for the default (as in use POSIX; ), you will import hundreds and hundreds of symbols into your namespace.

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.

FUNCTIONS

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

Note that when using threads and in Linux this is 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.
abort
This is identical to the C function abort() . It terminates the process with a SIGABRT signal unless caught by a signal handler or if the handler does not return normally (it e.g. does a longjmp ).
abs
This is identical to Perl's builtin abs() function, returning the absolute value of its numerical argument.
access
Determines the accessibility of a file.
```
	if( POSIX::access( "/", &POSIX::R_OK ) ){
		print "have read permission\n";
	}
```
Returns undef on failure. Note: do not use access() for security purposes. Between the access() call and the operation you are preparing for the permissions might change: a classic race condition.
acos
This is identical to the C function acos() , returning the arcus cosine of its numerical argument. See also Math::Trig.
acosh
This is identical to the C function acosh() , returning the hyperbolic arcus cosine of its numerical argument [C99]. See also Math::Trig.
alarm
This is identical to Perl's builtin alarm() function, either for arming or disarming the SIGARLM timer.
asctime
This is identical to the C function 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 $mon is zero-based: January equals 0 . The $year is 1900-based: 2001 equals 101 . $wday and $yday default to zero (and are usually ignored anyway), and $isdst defaults to -1.
asin
This is identical to the C function asin() , returning the arcus sine of its numerical argument. See also Math::Trig.
asinh
This is identical to the C function asinh() , returning the hyperbolic arcus sine of its numerical argument [C99]. See also Math::Trig.
assert
Unimplemented, but you can use die and the Carp module to achieve similar things.
atan
This is identical to the C function atan() , returning the arcus tangent of its numerical argument. See also Math::Trig.
atanh
This is identical to the C function atanh() , returning the hyperbolic arcus tangent of its numerical argument [C99]. See also Math::Trig.
atan2
This is identical to Perl's builtin atan2() function, returning the arcus tangent defined by its two numerical arguments, the y coordinate and the x coordinate. See also Math::Trig.
atexit
Not implemented. atexit() is C-specific: use END {} instead, see perlmod.
atof
Not implemented. 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.
atoi
Not implemented. 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 int.
atol
Not implemented. 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 int.
bsearch
bsearch() not supplied. For doing binary search on wordlists, see Search::Dict.
calloc
Not implemented. calloc() is C-specific. Perl does memory management transparently.
cbrt
The cube root [C99].
ceil
This is identical to the C function ceil() , returning the smallest integer value greater than or equal to the given numerical argument.
chdir
This is identical to Perl's builtin chdir() function, allowing one to change the working (default) directory, see chdir.
chmod
This is identical to Perl's builtin chmod() function, allowing one to change file and directory permissions, see chmod.
chown
This is identical to Perl's builtin chown() function, allowing one to change file and directory owners and groups, see chown.
clearerr
Not implemented. Use the method IO::Handle::clearerr() instead, to reset the error state (if any) and EOF state (if any) of the given stream.
clock
This is identical to the C function clock() , returning the amount of spent processor time in microseconds.
close
Close the file. This uses file descriptors such as those obtained by calling POSIX::open .
```
	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	POSIX::close( $fd );
```
Returns undef on failure.

See also close.
closedir
This is identical to Perl's builtin closedir() function for closing a directory handle, see closedir.
cos
This is identical to Perl's builtin cos() function, for returning the cosine of its numerical argument, see cos. See also Math::Trig.
cosh
This is identical to the C function cosh() , for returning the hyperbolic cosine of its numeric argument. See also Math::Trig.
copysign
Returns x but with the sign of y [C99].
```
 $x_with_sign_of_y = POSIX::copysign($x, $y);
```
See also signbit.
creat
Create a new file. This returns a file descriptor like the ones returned by POSIX::open . Use POSIX::close to close the file.
```
	$fd = POSIX::creat( "foo", 0611 );
	POSIX::close( $fd );
```
See also sysopen and its O_CREAT flag.
ctermid
Generates the path name for the controlling terminal.
```
	$path = POSIX::ctermid();
```
ctime
This is identical to the C function ctime() and equivalent to asctime(localtime(...)) , see asctime and localtime.
cuserid
Get the login name of the owner of the current process.
```
	$name = POSIX::cuserid();
```
difftime
This is identical to the C function difftime() , for returning the time difference (in seconds) between two times (as returned by time()), see time.
div
Not implemented. div() is C-specific, use int on the usual / division and the modulus % .
dup
This is similar to the C function dup() , for duplicating a file descriptor.

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

Returns undef on failure.
dup2
This is similar to the C function dup2() , for duplicating a file descriptor to an another known file descriptor.

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

Returns undef on failure.
erf
The error function [C99].
erfc
The complementary error function [C99].
errno
Returns the value of errno.
```
	$errno = POSIX::errno();
```
This identical to the numerical values of the $! , see $ERRNO in perlvar.
execl
Not implemented. execl() is C-specific, see exec.
execle
Not implemented. execle() is C-specific, see exec.
execlp
Not implemented. execlp() is C-specific, see exec.
execv
Not implemented. execv() is C-specific, see exec.
execve
Not implemented. execve() is C-specific, see exec.
execvp
Not implemented. execvp() is C-specific, see exec.
exit
This is identical to Perl's builtin exit() function for exiting the program, see exit.
exp
This is identical to Perl's builtin exp() function for returning the exponent (e-based) of the numerical argument, see exp.
expm1
Equivalent to exp(x) - 1 , but more precise for small argument values [C99].

See also log1p.
fabs
This is identical to Perl's builtin abs() function for returning the absolute value of the numerical argument, see abs.
fclose
Not implemented. Use method IO::Handle::close() instead, or see close.
fcntl
This is identical to Perl's builtin fcntl() function, see fcntl.
fdopen
Not implemented. Use method IO::Handle::new_from_fd() instead, or see open.
feof
Not implemented. Use method IO::Handle::eof() instead, or see eof.
ferror
Not implemented. Use method IO::Handle::error() instead.
fflush
Not implemented. Use method IO::Handle::flush() instead. See also $OUTPUT_AUTOFLUSH in perlvar.
fgetc
Not implemented. Use method IO::Handle::getc() instead, or see read.
fgetpos
Not implemented. Use method IO::Seekable::getpos() instead, or see seek.
fgets
Not implemented. Use method IO::Handle::gets() instead. Similar to <>, also known as readline.
fileno
Not implemented. Use method IO::Handle::fileno() instead, or see fileno.
floor
This is identical to the C function floor() , returning the largest integer value less than or equal to the numerical argument.
fdim
"Positive difference", x - y if x > y , zero otherwise [C99].
fegetround
Returns the current floating point rounding mode, one of
```
  FE_TONEAREST FE_TOWARDZERO FE_UPWARD FE_UPWARD
```
FE_TONEAREST is like round, FE_TOWARDZERO is like trunc [C99].
fesetround
Sets the floating point rounding mode, see fegetround [C99].
fma
"Fused multiply-add", x * y + z , possibly faster (and less lossy) than the explicit two operations [C99].
```
 my $fused = POSIX::fma($x, $y, $z);
```
fmax
Maximum of x and y, except when either is NaN , returns the other [C99].
```
 my $min = POSIX::fmax($x, $y);
```
fmin
Minimum of x and y, except when either is NaN , returns the other [C99].
```
 my $min = POSIX::fmin($x, $y);
```
fmod
This is identical to the C function fmod() .
```
	$r = fmod($x, $y);
```
It returns the remainder $r = $x - $n*$y , where $n = trunc($x/$y) . The $r has the same sign as $x and magnitude (absolute value) less than the magnitude of $y .
fopen
Not implemented. Use method IO::File::open() instead, or see open.
fork
This is identical to Perl's builtin fork() function for duplicating the current process, see fork and perlfork if you are in Windows.
fpathconf
Retrieves the value of a configurable limit on a file or directory. This uses file descriptors such as those obtained by calling POSIX::open .

The following will determine the maximum length of the longest allowable pathname on the filesystem which holds /var/foo.
```
	$fd = POSIX::open( "/var/foo", &POSIX::O_RDONLY );
	$path_max = POSIX::fpathconf($fd, &POSIX::_PC_PATH_MAX);
```
Returns undef on failure.
fpclassify
Returns one of
```
  FP_NORMAL FP_ZERO FP_SUBNORMAL FP_INFINITE FP_NAN
```
telling the class of the argument [C99]. FP_INFINITE is positive or negative infinity, FP_NAN is not-a-number. FP_SUBNORMAL means subnormal numbers (also known as denormals), very small numbers with low precision. FP_ZERO is zero. FP_NORMAL is all the rest.
fprintf
Not implemented. fprintf() is C-specific, see printf instead.
fputc
Not implemented. fputc() is C-specific, see print instead.
fputs
Not implemented. fputs() is C-specific, see print instead.
fread
Not implemented. fread() is C-specific, see read instead.
free
Not implemented. free() is C-specific. Perl does memory management transparently.
freopen
Not implemented. freopen() is C-specific, see open instead.
frexp
Return the mantissa and exponent of a floating-point number.
```
	($mantissa, $exponent) = POSIX::frexp( 1.234e56 );
```
fscanf
Not implemented. fscanf() is C-specific, use <> and regular expressions instead.
fseek
Not implemented. Use method IO::Seekable::seek() instead, or see seek.
fsetpos
Not implemented. Use method IO::Seekable::setpos() instead, or seek seek.
fstat
Get file status. This uses file descriptors such as those obtained by calling POSIX::open . The data returned is identical to the data from Perl's builtin stat function.
```
	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	@stats = POSIX::fstat( $fd );
```
fsync
Not implemented. Use method IO::Handle::sync() instead.
ftell
Not implemented. Use method IO::Seekable::tell() instead, or see tell.
fwrite
Not implemented. fwrite() is C-specific, see print instead.
getc
This is identical to Perl's builtin getc() function, see getc.
getchar
Returns one character from STDIN. Identical to Perl's getc(), see getc.
getcwd
Returns the name of the current working directory. See also Cwd.
getegid
Returns the effective group identifier. Similar to Perl' s builtin variable $( , see $EGID in perlvar.
getenv
Returns the value of the specified environment variable. The same information is available through the %ENV array.
geteuid
Returns the effective user identifier. Identical to Perl's builtin $> variable, see $EUID in perlvar.
getgid
Returns the user's real group identifier. Similar to Perl's builtin variable $) , see $GID in perlvar.
getgrgid
This is identical to Perl's builtin getgrgid() function for returning group entries by group identifiers, see getgrgid.
getgrnam
This is identical to Perl's builtin getgrnam() function for returning group entries by group names, see getgrnam.
getgroups
Returns the ids of the user's supplementary groups. Similar to Perl's builtin variable $) , see $GID in perlvar.
getlogin
This is identical to Perl's builtin getlogin() function for returning the user name associated with the current session, see getlogin.
getpayload
```
	use POSIX ':nan_payload';
	getpayload($var)
```
Returns the NaN payload.

Note the API instability warning in setpayload.

See nan for more discussion about NaN .
getpgrp
This is identical to Perl's builtin getpgrp() function for returning the process group identifier of the current process, see getpgrp.
getpid
Returns the process identifier. Identical to Perl's builtin variable $$ , see $PID in perlvar.
getppid
This is identical to Perl's builtin getppid() function for returning the process identifier of the parent process of the current process , see getppid.
getpwnam
This is identical to Perl's builtin getpwnam() function for returning user entries by user names, see getpwnam.
getpwuid
This is identical to Perl's builtin getpwuid() function for returning user entries by user identifiers, see getpwuid.
gets
Returns one line from STDIN , similar to <>, also known as the readline() function, see readline.

NOTE: if you have C programs that still use gets() , be very afraid. The gets() function is a source of endless grief because it has no buffer overrun checks. It should never be used. The fgets() function should be preferred instead.
getuid
Returns the user's identifier. Identical to Perl's builtin $< variable, see $UID in perlvar.
gmtime
This is identical to Perl's builtin gmtime() function for converting seconds since the epoch to a date in Greenwich Mean Time, see gmtime.
hypot
Equivalent to sqrt(x * x + y * y) except more stable on very large or very small arguments [C99].
ilogb
Integer binary logarithm [C99]

For example ilogb(20) is 4, as an integer.

See also logb.

Inf

The infinity as a constant:

   use POSIX qw(Inf);
   my $pos_inf = +Inf;  # Or just Inf.
   my $neg_inf = -Inf;

See also isinf, and fpclassify.

isalnum
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:alnum:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isalpha
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:alpha:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isatty
Returns a boolean indicating whether the specified filehandle is connected to a tty. Similar to the -t operator, see -X.
iscntrl
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:cntrl:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isdigit
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:digit:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isfinite
Returns true if the argument is a finite number (that is, not an infinity, or the not-a-number) [C99].

See also isinf, isnan, and fpclassify.
isgraph
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:graph:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isgreater
(Also isgreaterequal , isless , islessequal , islessgreater , isunordered )

Floating point comparisons which handle the NaN [C99].
isinf
Returns true if the argument is an infinity (positive or negative) [C99].

See also Inf, isnan, isfinite, and fpclassify.
islower
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:lower:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isnan
Returns true if the argument is NaN (not-a-number) [C99].

Note that you cannot test for "NaN -ness" with
```
   $x == $x
```
since the NaN is not equivalent to anything, including itself.

See also nan, NaN, isinf, and fpclassify.
isnormal
Returns true if the argument is normal (that is, not a subnormal/denormal, and not an infinity, or a not-a-number) [C99].

See also isfinite, and fpclassify.
isprint
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:print:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
ispunct
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:punct:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
issignaling
```
	use POSIX ':nan_payload';
	issignaling($var, $payload)
```
Return true if the argument is a signaling NaN.

Note the API instability warning in setpayload.

See nan for more discussion about NaN .
isspace
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:space:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isupper
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:upper:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
isxdigit
This function has been removed as of v5.24. It was very similar to matching against qr/ ^ [[:xdigit:]]+ $ /x , which you should convert to use instead. See POSIX Character Classes in perlrecharclass.
j0
j1
jn
y0
y1
yn
The Bessel function of the first kind of the order zero.
kill
This is identical to Perl's builtin kill() function for sending signals to processes (often to terminate them), see kill.
labs
Not implemented. (For returning absolute values of long integers.) labs() is C-specific, see abs instead.
lchown
This is identical to the C function, except the order of arguments is consistent with Perl's builtin chown() with the added restriction of only one path, not a list of paths. Does the same thing as the chown() function but changes the owner of a symbolic link instead of the file the symbolic link points to.
```
 POSIX::lchown($uid, $gid, $file_path);
```
ldexp
This is identical to the C function ldexp() for multiplying floating point numbers with powers of two.
```
	$x_quadrupled = POSIX::ldexp($x, 2);
```
ldiv
Not implemented. (For computing dividends of long integers.) ldiv() is C-specific, use / and int() instead.
lgamma
The logarithm of the Gamma function [C99].

See also tgamma.
log1p
Equivalent to log(1 + x) , but more stable results for small argument values [C99].
log2
Logarithm base two [C99].

See also expm1.
logb
Integer binary logarithm [C99].

For example logb(20) is 4, as a floating point number.

See also ilogb.
link
This is identical to Perl's builtin link() function for creating hard links into files, see link.

localeconv

Get numeric formatting information. Returns a reference to a hash containing the current underlying locale's formatting values. Users of this function should also read perllocale, which provides a comprehensive discussion of Perl locale handling, including a section devoted to this function.

Here is how to query the database for the 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
		int_p_cs_precedes
		int_p_sep_by_space
		int_n_cs_precedes
		int_n_sep_by_space
		int_p_sign_posn
		int_n_sign_posn
	))
	{
		printf qq(%s: "%s",\n),
			$property, $lconv->{$property};
	}

The members whose names begin with int_p_ and int_n_ were added by POSIX.1-2008 and are only available on systems that support them.

localtime
This is identical to Perl's builtin localtime() function for converting seconds since the epoch to a date see localtime.
log
This is identical to Perl's builtin log() function, returning the natural (e-based) logarithm of the numerical argument, see log.

log10

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

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

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

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

longjmp
Not implemented. longjmp() is C-specific: use die instead.
lseek
Move the file's read/write position. This uses file descriptors such as those obtained by calling POSIX::open .
```
	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	$off_t = POSIX::lseek( $fd, 0, &POSIX::SEEK_SET );
```
Returns undef on failure.
lrint
Depending on the current floating point rounding mode, rounds the argument either toward nearest (like round), toward zero (like trunc), downward (toward negative infinity), or upward (toward positive infinity) [C99].

For the rounding mode, see fegetround.
lround
Like round, but as integer, as opposed to floating point [C99].

See also ceil, floor, trunc.

Owing to an oversight, this is not currently exported by default, or as part of the :math_h_c99 export tag; importing it must therefore be done by explicit name.
malloc
Not implemented. malloc() is C-specific. Perl does memory management transparently.
mblen
This is identical to the C function mblen() .

Core Perl does not have any support for the wide and multibyte characters of the C standards, except under UTF-8 locales, so this might be a rather useless function.

However, Perl supports Unicode, see perluniintro.
mbstowcs
This is identical to the C function mbstowcs() .

See mblen.
mbtowc
This is identical to the C function mbtowc() .

See mblen.
memchr
Not implemented. memchr() is C-specific, see index instead.
memcmp
Not implemented. memcmp() is C-specific, use eq instead, see perlop.
memcpy
Not implemented. memcpy() is C-specific, use = , see perlop, or see substr.
memmove
Not implemented. memmove() is C-specific, use = , see perlop, or see substr.
memset
Not implemented. memset() is C-specific, use x instead, see perlop.
mkdir
This is identical to Perl's builtin mkdir() function for creating directories, see mkdir.
mkfifo
This is similar to the C function mkfifo() for creating FIFO special files.
```
	if (mkfifo($path, $mode)) { ....
```
Returns undef on failure. The $mode is similar to the mode of mkdir(), see mkdir, though for mkfifo you must specify the $mode .
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 (mon ), weekday (wday ), and yearday (yday ) begin at zero, i.e., January is 0, not 1; Sunday is 0, not 1; January 1st is 0, not 1. The year (year ) is given in years since 1900; i.e., the year 1995 is 95; the year 2001 is 101. Consult your system's 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 undef on failure.
modf
Return the integral and fractional parts of a floating-point number.
```
	($fractional, $integral) = POSIX::modf( 3.14 );
```
See also round.
NaN
The not-a-number as a constant:
```
   use POSIX qw(NaN);
   my $nan = NaN;
```
See also nan, /isnan , and fpclassify.
nan
```
   my $nan = nan();
```
Returns NaN , not-a-number [C99].

The returned NaN is always a quiet NaN, as opposed to signaling.

With an argument, can be used to generate a NaN with payload. The argument is first interpreted as a floating point number, but then any fractional parts are truncated (towards zero), and the value is interpreted as an unsigned integer. The bits of this integer are stored in the unused bits of the NaN.

The result has a dual nature: it is a NaN, but it also carries the integer inside it. The integer can be retrieved with getpayload. Note, though, that the payload is not propagated, not even on copies, and definitely not in arithmetic operations.

How many bits fit in the NaN depends on what kind of floating points are being used, but on the most common platforms (64-bit IEEE 754, or the x86 80-bit long doubles) there are 51 and 61 bits available, respectively. (There would be 52 and 62, but the quiet/signaling bit of NaNs takes away one.) However, because of the floating-point-to- integer-and-back conversions, please test carefully whether you get back what you put in. If your integers are only 32 bits wide, you probably should not rely on more than 32 bits of payload.

Whether a "signaling" NaN is in any way different from a "quiet" NaN, depends on the platform. Also note that the payload of the default NaN (no argument to nan()) is not necessarily zero, use setpayload to explicitly set the payload. On some platforms like the 32-bit x86, (unless using the 80-bit long doubles) the signaling bit is not supported at all.

See also isnan, NaN, setpayload and issignaling.
nearbyint
Returns the nearest integer to the argument, according to the current rounding mode (see fegetround) [C99].
nextafter
Returns the next representable floating point number after x in the direction of y [C99].
```
 my $nextafter = POSIX::nextafter($x, $y);
```
Like nexttoward, but potentially less accurate.
nexttoward
Returns the next representable floating point number after x in the direction of y [C99].
```
 my $nexttoward = POSIX::nexttoward($x, $y);
```
Like nextafter, but potentially more accurate.
nice
This is similar to the C function nice() , for changing the scheduling preference of the current process. Positive arguments mean a more polite process, negative values a more needy process. Normal (non-root) user processes can only change towards being more polite.

Returns undef on failure.
offsetof
Not implemented. offsetof() is C-specific, you probably want to see pack instead.
open
Open a file for reading for writing. This returns file descriptors, not Perl filehandles. Use 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 undef on failure.

See also sysopen.

opendir

Open a directory for reading.

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

Returns undef on failure.

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 /var.
```
	$path_max = POSIX::pathconf( "/var",
				      &POSIX::_PC_PATH_MAX );
```
Returns undef on failure.
pause
This is similar to the C function pause() , which suspends the execution of the current process until a signal is received.

Returns undef on failure.
perror
This is identical to the C function perror() , which outputs to the standard error stream the specified message followed by ": " and the current error string. Use the warn() function and the $! variable instead, see warn and $ERRNO in perlvar.

pipe

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

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

CLASSES

`POSIX::SigAction`

new
Creates a new POSIX::SigAction object which corresponds to the 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 POSIX::SigSet object, it defaults to the empty set. The third parameter contains the sa_flags , it defaults to 0.
```
	$sigset = POSIX::SigSet->new(SIGINT, SIGQUIT);
	$sigaction = POSIX::SigAction->new(
			\&handler, $sigset, &POSIX::SA_NOCLDSTOP
		     );
```
This POSIX::SigAction object is intended for use with the POSIX::sigaction() function.

handler
mask

flags

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

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

safe
accessor function for the "safe signals" flag of a SigAction object; see 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 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 POSIX::sigaction() :
```
	sigaction(SIGINT, $new_action, $old_action);
	if ($old_action->safe) {
	    # previous SIGINT handler used safe signals
	}
```

`POSIX::SigRt`

%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 delete and exists on the elements, and use scalar on the %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 local on $POSIX::SigRt::SIGACTION_FLAGS , or you can derive from POSIX::SigRt and define your own new() (the tied hash STORE method of the %SIGRT calls new($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).

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.
SIGRTMIN
Return the minimum POSIX realtime signal number available, or undef if no POSIX realtime signals are available.
SIGRTMAX
Return the maximum POSIX realtime signal number available, or undef if no POSIX realtime signals are available.

`POSIX::SigSet`

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 );
```
addset
Add a signal to a SigSet object.
```
	$sigset->addset( &POSIX::SIGUSR2 );
```
Returns undef on failure.
delset
Remove a signal from the SigSet object.
```
	$sigset->delset( &POSIX::SIGUSR2 );
```
Returns undef on failure.
emptyset
Initialize the SigSet object to be empty.
```
	$sigset->emptyset();
```
Returns undef on failure.
fillset
Initialize the SigSet object to include all signals.
```
	$sigset->fillset();
```
Returns undef on failure.

ismember

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

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

`POSIX::Termios`

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;
```
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 undef on failure.
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);
```
getcflag
Retrieve the c_cflag field of a termios object.
```
	$c_cflag = $termios->getcflag;
```
getiflag
Retrieve the c_iflag field of a termios object.
```
	$c_iflag = $termios->getiflag;
```
getispeed
Retrieve the input baud rate.
```
	$ispeed = $termios->getispeed;
```
getlflag
Retrieve the c_lflag field of a termios object.
```
	$c_lflag = $termios->getlflag;
```
getoflag
Retrieve the c_oflag field of a termios object.
```
	$c_oflag = $termios->getoflag;
```
getospeed
Retrieve the output baud rate.
```
	$ospeed = $termios->getospeed;
```
setattr
Set terminal control attributes.

Set attributes immediately for stdout.
```
	$termios->setattr( 1, &POSIX::TCSANOW );
```
Returns undef on failure.
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 );
```

setcflag

Set the c_cflag field of a termios object.

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

setiflag

Set the c_iflag field of a termios object.

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

setispeed
Set the input baud rate.
```
	$termios->setispeed( &POSIX::B9600 );
```
Returns undef on failure.

setlflag

Set the c_lflag field of a termios object.

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

setoflag

Set the c_oflag field of a termios object.

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

setospeed
Set the output baud rate.
```
	$termios->setospeed( &POSIX::B9600 );
```
Returns undef on failure.
Baud rate values
B38400 B75 B200 B134 B300 B1800 B150 B0 B19200 B1200 B9600 B600 B4800 B50 B2400 B110
Terminal interface values
TCSADRAIN TCSANOW TCOON TCIOFLUSH TCOFLUSH TCION TCIFLUSH TCSAFLUSH TCIOFF TCOOFF
c_cc field values
VEOF VEOL VERASE VINTR VKILL VQUIT VSUSP VSTART VSTOP VMIN VTIME NCCS
c_cflag field values
CLOCAL CREAD CSIZE CS5 CS6 CS7 CS8 CSTOPB HUPCL PARENB PARODD
c_iflag field values
BRKINT ICRNL IGNBRK IGNCR IGNPAR INLCR INPCK ISTRIP IXOFF IXON PARMRK
c_lflag field values
ECHO ECHOE ECHOK ECHONL ICANON IEXTEN ISIG NOFLSH TOSTOP
c_oflag field values
OPOST

PATHNAME CONSTANTS

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

POSIX CONSTANTS

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

SYSTEM CONFIGURATION

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

ERRNO

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

FCNTL

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

FLOAT

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

FLOATING-POINT ENVIRONMENT

Constants
FE_DOWNWARD FE_TONEAREST FE_TOWARDZERO FE_UPWARD on systems that support them.

LIMITS

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

LOCALE

Constants
LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME LC_MESSAGES on systems that support them.

MATH

Constants
HUGE_VAL

FP_ILOGB0 FP_ILOGBNAN FP_INFINITE FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO INFINITY NAN Inf NaN M_1_PI M_2_PI M_2_SQRTPI M_E M_LN10 M_LN2 M_LOG10E M_LOG2E M_PI M_PI_2 M_PI_4 M_SQRT1_2 M_SQRT2 on systems with C99 support.

SIGNAL

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 ILL_ILLOPC ILL_ILLOPN ILL_ILLADR ILL_ILLTRP ILL_PRVOPC ILL_PRVREG ILL_COPROC ILL_BADSTK FPE_INTDIV FPE_INTOVF FPE_FLTDIV FPE_FLTOVF FPE_FLTUND FPE_FLTRES FPE_FLTINV FPE_FLTSUB SEGV_MAPERR SEGV_ACCERR BUS_ADRALN BUS_ADRERR BUS_OBJERR TRAP_BRKPT TRAP_TRACE CLD_EXITED CLD_KILLED CLD_DUMPED CLD_TRAPPED CLD_STOPPED CLD_CONTINUED POLL_IN POLL_OUT POLL_MSG POLL_ERR POLL_PRI POLL_HUP SI_USER SI_QUEUE SI_TIMER SI_ASYNCIO SI_MESGQ

STAT

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
Macros
S_ISBLK S_ISCHR S_ISDIR S_ISFIFO S_ISREG

STDLIB

Constants
EXIT_FAILURE EXIT_SUCCESS MB_CUR_MAX RAND_MAX

STDIO

Constants
BUFSIZ EOF FILENAME_MAX L_ctermid L_cuserid TMP_MAX

TIME

Constants
CLK_TCK CLOCKS_PER_SEC

UNISTD

Constants
R_OK SEEK_CUR SEEK_END SEEK_SET STDIN_FILENO STDOUT_FILENO STDERR_FILENO W_OK X_OK

WAIT

Constants
WNOHANG WUNTRACED
- WNOHANG
  Do not suspend the calling process until a child process changes state but instead return immediately.
- WUNTRACED
  Catch stopped child processes.
Macros
WIFEXITED WEXITSTATUS WIFSIGNALED WTERMSIG WIFSTOPPED WSTOPSIG
- WIFEXITED
  WIFEXITED(${^CHILD_ERROR_NATIVE}) returns true if the child process exited normally (exit() or by falling off the end of main() )
- WEXITSTATUS
  WEXITSTATUS(${^CHILD_ERROR_NATIVE}) returns the normal exit status of the child process (only meaningful if WIFEXITED(${^CHILD_ERROR_NATIVE}) is true)
- WIFSIGNALED
  WIFSIGNALED(${^CHILD_ERROR_NATIVE}) returns true if the child process terminated because of a signal
- WTERMSIG
  WTERMSIG(${^CHILD_ERROR_NATIVE}) returns the signal the child process terminated for (only meaningful if WIFSIGNALED(${^CHILD_ERROR_NATIVE}) is true)
- WIFSTOPPED
  WIFSTOPPED(${^CHILD_ERROR_NATIVE}) returns true if the child process is currently stopped (can happen only if you specified the WUNTRACED flag to waitpid())
- WSTOPSIG
  WSTOPSIG(${^CHILD_ERROR_NATIVE}) returns the signal the child process was stopped for (only meaningful if WIFSTOPPED(${^CHILD_ERROR_NATIVE}) is true)

WINSOCK

(Windows only.)

Constants
WSAEINTR WSAEBADF WSAEACCES WSAEFAULT WSAEINVAL WSAEMFILE WSAEWOULDBLOCK WSAEINPROGRESS WSAEALREADY WSAENOTSOCK WSAEDESTADDRREQ WSAEMSGSIZE WSAEPROTOTYPE WSAENOPROTOOPT WSAEPROTONOSUPPORT WSAESOCKTNOSUPPORT WSAEOPNOTSUPP WSAEPFNOSUPPORT WSAEAFNOSUPPORT WSAEADDRINUSE WSAEADDRNOTAVAIL WSAENETDOWN WSAENETUNREACH WSAENETRESET WSAECONNABORTED WSAECONNRESET WSAENOBUFS WSAEISCONN WSAENOTCONN WSAESHUTDOWN WSAETOOMANYREFS WSAETIMEDOUT WSAECONNREFUSED WSAELOOP WSAENAMETOOLONG WSAEHOSTDOWN WSAEHOSTUNREACH WSAENOTEMPTY WSAEPROCLIM WSAEUSERS WSAEDQUOT WSAESTALE WSAEREMOTE WSAEDISCON WSAENOMORE WSAECANCELLED WSAEINVALIDPROCTABLE WSAEINVALIDPROVIDER WSAEPROVIDERFAILEDINIT WSAEREFUSED

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