POSIX(3p)

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;

    my $sess_id = POSIX::setsid();

    my $fd = POSIX::open($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 or almost 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.

The notation "[C99]" indicates functions that were added in the ISO/IEC 9899:1999 version of the C language standard. Some may not be available on your system if it adheres to an earlier standard. Attempts to use any missing one will result in a fatal runtime error message.

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 (except that POSIX::abs() must be provided an explicit value (rather than relying on an implicit $_):

        $absolute_value = POSIX::abs(42);   # good

        $absolute_value = POSIX::abs();     # throws exception

"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. Added in Perl v5.22.

"alarm"
    This is identical to Perl's builtin alarm() function, either for arming or disarming the "SIGARLM" timer, except that POSIX::alarm() must be provided an explicit value (rather than relying on an implicit $_):

        POSIX::alarm(3)     # good

        POSIX::alarm()      # throws exception

"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.

    Note the result is always in English. Use "strftime" instead to get a result suitable for the current locale. That function's %c format yields the locale's preferred representation.

"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. Added in Perl v5.22.

"assert"
    Unimplemented, but you can use "die" in perlfunc 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. Added in Perl v5.22.

"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" in perlfunc.

"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" in perlfunc.

"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]. Added in Perl v5.22.

"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" in perlfunc -- with the exception that POSIX::chdir() must be provided an explicit value (rather than relying on an implicit $_):

        $rv = POSIX::chdir('path/to/dir');      # good

        $rv = POSIX::chdir();                   # throws exception

"chmod"
    This is identical to Perl's builtin chmod() function, allowing one to change file and directory permissions -- see "chmod" in perlfunc -- with the exception that POSIX::chmod() can only change one file at a time (rather than a list of files):

        $c = chmod 0664, $file1, $file2;          # good

        $c = POSIX::chmod 0664, $file1;           # throws exception

        $c = POSIX::chmod 0664, $file1, $file2;   # throws exception

    As with the built-in chmod(), $file may be a filename or a file handle.

"chown"
    This is identical to Perl's builtin chown() function, allowing one to change file and directory owners and groups, see "chown" in perlfunc.

"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" in perlfunc.

"closedir"
    This is identical to Perl's builtin closedir() function for closing a directory handle, see "closedir" in perlfunc.

"cos"
    This is identical to Perl's builtin cos() function for returning the cosine of its numerical argument -- except that POSIX::cos() must be provided with an explicit value (rather than relying on an implicit $_):

        $cosine = POSIX::cos(3);    # good

        $cosine = POSIX::cos();     # throws exception

    See "cos" in perlfunc; 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]. Added in Perl v5.22.

     $x_with_sign_of_y = POSIX::copysign($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" in perlfunc 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" [POSIX.1-1988]
    Get the login name of the owner of the current process.

            $name = POSIX::cuserid();

    Note: this function has not been specified by POSIX since 1990 and is included only for backwards compatibility. New code should use getlogin() instead.

"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" in perlfunc 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]. Added in Perl v5.22.

"erfc"
    The complementary error function [C99]. Added in Perl v5.22.

"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" in perlfunc.

"execle"
    Not implemented. execle() is C-specific, see "exec" in perlfunc.

"execlp"
    Not implemented. execlp() is C-specific, see "exec" in perlfunc.

"execv"
    Not implemented. execv() is C-specific, see "exec" in perlfunc.

"execve"
    Not implemented. execve() is C-specific, see "exec" in perlfunc.

"execvp"
    Not implemented. execvp() is C-specific, see "exec" in perlfunc.

"exit"
    This is identical to Perl's builtin exit() function for exiting the program, see "exit" in perlfunc.

"exp"
    This is identical to Perl's builtin exp() function for returning the exponent (e-based) of the numerical argument -- except that POSIX::exp() must be provided with an explicit value (rather than relying on an implicit $_):

        $exp = POSIX::exp(3);    # good

        $exp = POSIX::exp();     # throws exception

    See "exp" in perlfunc.

"expm1"
    Equivalent to "exp(x) - 1", but more precise for small argument values [C99]. Added in Perl v5.22.

    See also "log1p".

"fabs"
    This is identical to Perl's builtin abs() function for returning the absolute value of the numerical argument -- except that POSIX::fabs() must be provided with an explicit value (rather than relying on an implicit $_):

        $absolute_value = POSIX::fabs(3);    # good

        $absolute_value = POSIX::fabs();     # throws exception

    See "abs" in perlfunc.

    This is identical to Perl's builtin cos() function for returning the cosine =item "fclose"

    Not implemented. Use method IO::Handle::close() instead, or see "close" in perlfunc.

"fcntl"
    This is identical to Perl's builtin fcntl() function, see "fcntl" in perlfunc.

"fdopen"
    Not implemented. Use method IO::Handle::new_from_fd() instead, or see "open" in perlfunc.

"feof"
    Not implemented. Use method IO::Handle::eof() instead, or see "eof" in perlfunc.

"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" in perlfunc.

"fgetpos"
    Not implemented. Use method IO::Seekable::getpos() instead, or see "seek" in perlfunc.

"fgets"
    Not implemented. Use method IO::Handle::gets() instead. Similar to <>, also known as "readline" in perlfunc.

"fileno"
    Not implemented. Use method IO::Handle::fileno() instead, or see "fileno" in perlfunc.

"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]. Added in Perl v5.22.

"fegetround"
    Returns the current floating point rounding mode, one of

      FE_TONEAREST FE_TOWARDZERO FE_UPWARD FE_DOWNWARD

    "FE_TONEAREST" is like "round", "FE_TOWARDZERO" is like "trunc" [C99]. Added in Perl v5.22.

"fesetround"
    Sets the floating point rounding mode, see "fegetround" [C99]. Added in Perl v5.22.

"fma"
    "Fused multiply-add", "x * y + z", possibly faster (and less lossy) than the explicit two operations [C99]. Added in Perl v5.22.

     my $fused = POSIX::fma($x, $y, $z);

"fmax"
    Maximum of "x" and "y", except when either is "NaN", returns the other [C99]. Added in Perl v5.22.

     my $max = POSIX::fmax($x, $y);

"fmin"
    Minimum of "x" and "y", except when either is "NaN", returns the other [C99]. Added in Perl v5.22.

     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" in perlfunc.

"fork"
    This is identical to Perl's builtin fork() function for duplicating the current process, see "fork" in perlfunc 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. Added in Perl v5.22.

"fprintf"
    Not implemented. fprintf() is C-specific, see "printf" in perlfunc instead.

"fputc"
    Not implemented. fputc() is C-specific, see "print" in perlfunc instead.

"fputs"
    Not implemented. fputs() is C-specific, see "print" in perlfunc instead.

"fread"
    Not implemented. fread() is C-specific, see "read" in perlfunc instead.

"free"
    Not implemented. free() is C-specific. Perl does memory management transparently.

"freopen"
    Not implemented. freopen() is C-specific, see "open" in perlfunc 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" in perlfunc.

"fsetpos"
    Not implemented. Use method IO::Seekable::setpos() instead, or seek "seek" in perlfunc.

"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" in perlfunc.

"fwrite"
    Not implemented. fwrite() is C-specific, see "print" in perlfunc instead.

"getc"
    This is identical to Perl's builtin getc() function, see "getc" in perlfunc.

"getchar"
    Returns one character from STDIN. Identical to Perl's getc(), see "getc" in perlfunc.

"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" in perlfunc.

"getgrnam"
    This is identical to Perl's builtin getgrnam() function for returning group entries by group names, see "getgrnam" in perlfunc.

"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" in perlfunc.

"getpayload"
            use POSIX ':nan_payload';
            getpayload($var)

    Returns the "NaN" payload. Added in Perl v5.24.

    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" in perlfunc.

"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" in perlfunc.

"getpwnam"
    This is identical to Perl's builtin getpwnam() function for returning user entries by user names, see "getpwnam" in perlfunc.

"getpwuid"
    This is identical to Perl's builtin getpwuid() function for returning user entries by user identifiers, see "getpwuid" in perlfunc.

"gets"
    Returns one line from "STDIN", similar to <>, also known as the readline() function, see "readline" in perlfunc.

    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" in perlfunc.

"hypot"
    Equivalent to "sqrt(x * x + y * y)" except more stable on very large or very small arguments [C99]. Added in Perl v5.22.

"ilogb"
    Integer binary logarithm [C99]. Added in Perl v5.22.

    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 Perl 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 Perl 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" in perlfunc.

"iscntrl"
    This function has been removed as of Perl 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 Perl 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]. Added in Perl v5.22.

    See also "isinf", "isnan", and "fpclassify".

"isgraph"
    This function has been removed as of Perl 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]. Added in Perl v5.22.

"isinf"
    Returns true if the argument is an infinity (positive or negative) [C99]. Added in Perl v5.22.

    See also "Inf", "isnan", "isfinite", and "fpclassify".

"islower"
    This function has been removed as of Perl 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]. Added in Perl v5.22.

    Note that you can also test for ""NaN"-ness" with equality operators ("==" or "!="), as in

        print "x is not a NaN\n" if $x == $x;

    since the "NaN" is not equal 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]. Added in Perl v5.22.

    See also "isfinite", and "fpclassify".

"isprint"
    This function has been removed as of Perl 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 Perl 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. Added in Perl v5.24.

    Note the API instability warning in "setpayload".

    See "nan" for more discussion about "NaN".

"isspace"
    This function has been removed as of Perl 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 Perl 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 Perl 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" in perlfunc.

"labs"
    Not implemented. (For returning absolute values of long integers.) labs() is C-specific, see "abs" in perlfunc 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]. Added in Perl v5.22.

    See also "tgamma".

"log1p"
    Equivalent to "log(1 + x)", but more stable results for small argument values [C99]. Added in Perl v5.22.

"log2"
    Logarithm base two [C99]. Added in Perl v5.22.

    See also "expm1".

"logb"
    Integer binary logarithm [C99]. Added in Perl v5.22.

    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" in perlfunc.

"localeconv"
    Get numeric formatting information. Returns a reference to a hash containing the formatting values of the locale that currently underlies the program, regardless of whether or not it is called from within the scope of a "use locale". Users of this function should also read perllocale, which provides a comprehensive discussion of Perl locale handling, including a section devoted to this function. Prior to Perl 5.28, or when operating in a non thread-safe environment, it should not be used in a threaded application unless it's certain that the underlying locale is C or POSIX. This is because it otherwise changes the locale, which globally affects all threads simultaneously. Windows platforms starting with Visual Studio 2005 are mostly thread-safe, but use of this function in those prior to Visual Studio 2015 can have a race with a thread that has called "switch_to_global_locale" in perlapi.

    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.

    A value of -1 returned for numeric entries indicates that the field is not applicable to the locale. This is rare except in the C and related locales, which don't have most monetary values defined. It can also happen, quirkily, in fields that are otherwise boolean to indicate that the value is kind of neither true nor false. This happens in "p_cs_precedes" and "int_p_cs_precedes" when the currency symbol neither precedes nor succeeds a positive value but is infixed, by replacing the radix character.

    Prior to Perl v5.37.7, empty string fields and numeric fields with value -1 were omitted from the returned hash.

"localtime"
    This is identical to Perl's builtin localtime() function for converting seconds since the epoch to a date see "localtime" in perlfunc except that POSIX::localtime() must be provided an explicit value (rather than relying on an implicit $_):

        @localtime = POSIX::localtime(time);    # good

        @localtime = localtime();               # good

        @localtime = POSIX::localtime();        # throws exception

"log"
    This is identical to Perl's builtin log() function for returning the natural (e-based) logarithm of the numerical argument -- except that POSIX::log() must be provided with an explicit value (rather than relying on an implicit $_):

        $log = POSIX::log(3);    # good

        $log = POSIX::log();     # throws exception

    See "log" in perlfunc.

"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) }

    or

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

    or

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

"longjmp"
    Not implemented. longjmp() is C-specific: use "die" in perlfunc 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]. Added in Perl v5.22.

    For the rounding mode, see "fegetround".

"lround"
    Like "round", but as integer, as opposed to floating point [C99]. Added in Perl v5.22.

    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 the same as the C function mblen() on unthreaded perls. On threaded perls, it transparently (almost) substitutes the more thread-safe "mbrlen(3)", if available, instead of "mblen".

    Core Perl does not have any support for wide and multibyte locales, except Unicode UTF-8 locales. This function, in conjunction with "mbtowc" and "wctomb" may be used to roll your own decoding/encoding of other types of multi-byte locales.

    Use "undef" as the first parameter to this function to get the effect of passing NULL as the first parameter to "mblen". This resets any shift state to its initial value. The return value is undefined if "mbrlen" was substituted, so you should never rely on it.

    When the first parameter is a scalar containing a value that either is a PV string or can be forced into one, the return value is the number of bytes occupied by the first character of that string; or 0 if that first character is the wide NUL character; or negative if there is an error. This is based on the locale that currently underlies the program, regardless of whether or not the function is called from Perl code that is within the scope of "use locale". Perl makes no attempt at hiding from your code any differences in the "errno" setting between "mblen" and "mbrlen". It does set "errno" to 0 before calling them.

    The optional second parameter is ignored if it is larger than the actual length of the first parameter string.

"mbtowc"
    This is the same as the C function mbtowc() on unthreaded perls. On threaded perls, it transparently (almost) substitutes the more thread-safe "mbrtowc(3)", if available, instead of "mbtowc".

    Core Perl does not have any support for wide and multibyte locales, except Unicode UTF-8 locales. This function, in conjunction with "mblen" and "wctomb" may be used to roll your own decoding/encoding of other types of multi-byte locales.

    The first parameter is a scalar into which, upon success, the wide character represented by the multi-byte string contained in the second parameter is stored. The optional third parameter is ignored if it is larger than the actual length of the second parameter string.

    Use "undef" as the second parameter to this function to get the effect of passing NULL as the second parameter to "mbtowc". This ignores the first parameter, and resets any shift state to its initial value. The return value is undefined if "mbrtowc" was substituted, so you should never rely on it.

    When the second parameter is a scalar containing a value that either is a PV string or can be forced into one, the return value is the number of bytes occupied by the first character of that string; or 0 if that first character is the wide NUL character; or negative if there is an error. This is based on the locale that currently underlies the program, regardless of whether or not the function is called from Perl code that is within the scope of "use locale". Perl makes no attempt at hiding from your code any differences in the "errno" setting between "mbtowc" and "mbrtowc". It does set "errno" to 0 before calling them.

"memchr"
    Not implemented. memchr() is C-specific, see "index" in perlfunc 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" in perlfunc.

"memmove"
    Not implemented. memmove() is C-specific, use "=", see perlop, or see "substr" in perlfunc.

"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" in perlfunc.

"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" in perlfunc, 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]. Added in Perl v5.22.

    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]. Added in Perl v5.22.

"nextafter"
    Returns the next representable floating point number after "x" in the direction of "y" [C99]. Added in Perl v5.22.

     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]. Added in Perl v5.22.

     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" in perlfunc 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" in perlfunc.

"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 $! variable instead, see "warn" in perlfunc and "$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 );

    See also "pipe" in perlfunc.

"pow"
    Computes $x raised to the power $exponent.

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

    You can also use the "**" operator, see perlop.

"printf"
    Formats and prints the specified arguments to "STDOUT". See also "printf" in perlfunc.

"putc"
    Not implemented. putc() is C-specific, see "print" in perlfunc instead.

"putchar"
    Not implemented. putchar() is C-specific, see "print" in perlfunc instead.

"puts"
    Not implemented. puts() is C-specific, see "print" in perlfunc instead.

"qsort"
    Not implemented. qsort() is C-specific, see "sort" in perlfunc instead.

"raise"
    Sends the specified signal to the current process. See also "kill" in perlfunc and the $$ in "$PID" in perlvar.

"rand"
    Not implemented. rand() is non-portable, see "rand" in perlfunc instead.

"read"
    Read from a file. This uses file descriptors such as those obtained by calling "POSIX::open". If the buffer $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 "undef" on failure.

    See also "sysread" in perlfunc.

"readdir"
    This is identical to Perl's builtin readdir() function for reading directory entries, see "readdir" in perlfunc.

"realloc"
    Not implemented. realloc() is C-specific. Perl does memory management transparently.

"remainder"
    Given "x" and "y", returns the value "x - n*y", where "n" is the integer closest to "x"/"y" [C99]. Added in Perl v5.22.

     my $remainder = POSIX::remainder($x, $y)

    See also "remquo".

"remove"
    Deletes a name from the filesystem. Calls "unlink" in perlfunc for files and "rmdir" in perlfunc for directories.

"remquo"
    Like "remainder" but also returns the low-order bits of the quotient (n) [C99]. Added in Perl v5.22.

    (This is quite esoteric interface, mainly used to implement numerical algorithms.)

"rename"
    This is identical to Perl's builtin rename() function for renaming files, see "rename" in perlfunc.

"rewind"
    Seeks to the beginning of the file.

"rewinddir"
    This is identical to Perl's builtin rewinddir() function for rewinding directory entry streams, see "rewinddir" in perlfunc.

"rint"
    Identical to "lrint".

"rmdir"
    This is identical to Perl's builtin rmdir() function for removing (empty) directories, see "rmdir" in perlfunc.

"round"
    Returns the integer (but still as floating point) nearest to the argument [C99]. Added in Perl v5.22.

    See also "ceil", "floor", "lround", "modf", and "trunc".

"scalbn"
    Returns "x * 2**y" [C99]. Added in Perl v5.22.

    See also "frexp" and "ldexp".

"scanf"
    Not implemented. scanf() is C-specific, use <> and regular expressions instead, see perlre.

"setgid"
    Sets the real group identifier and the effective group identifier for this process. Similar to assigning a value to the Perl's builtin $) variable, see "$EGID" in perlvar, 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.

"setjmp"
    Not implemented. setjmp() is C-specific: use "eval {}" instead, see "eval" in perlfunc.

"setlocale"
    WARNING! Prior to Perl 5.28 or on a system that does not support thread-safe locale operations, do NOT use this function in a thread. The locale will change in all other threads at the same time, and should your thread get paused by the operating system, and another started, that thread will not have the locale it is expecting. On some platforms, there can be a race leading to segfaults if two threads call this function nearly simultaneously. This warning does not apply on unthreaded builds, or on perls where "${^SAFE_LOCALES}" exists and is non-zero; namely Perl 5.28 and later compiled to be locale-thread-safe.

    This function modifies and queries the program's underlying locale. Users of this function should read perllocale, whch provides a comprehensive discussion of Perl locale handling, knowledge of which is necessary to properly use this function. It contains a section devoted to this function. The discussion here is merely a summary reference for setlocale(). Note that Perl itself is almost entirely unaffected by the locale except within the scope of "use locale". (Exceptions are listed in "Not within the scope of "use locale"" in perllocale, and locale-dependent functions within the POSIX module ARE always affected by the current 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").

            $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 ""). Please see your system's setlocale(3) documentation for the locale environment variables' meaning or consult perllocale.

            $loc = setlocale( LC_CTYPE, "" );

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

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

"setpayload"
            use POSIX ':nan_payload';
            setpayload($var, $payload);

    Sets the "NaN" payload of var. Added in Perl v5.24.

    NOTE: the NaN payload APIs are based on the latest (as of June 2015) proposed ISO C interfaces, but they are not yet a standard. Things may change.

    See "nan" for more discussion about "NaN".

    See also "setpayloadsig", "isnan", "getpayload", and "issignaling".

"setpayloadsig"
            use POSIX ':nan_payload';
            setpayloadsig($var, $payload);

    Like "setpayload" but also makes the NaN signaling. Added in Perl v5.24.

    Depending on the platform the NaN may or may not behave differently.

    Note the API instability warning in "setpayload".

    Note that because how the floating point formats work out, on the most common platforms signaling payload of zero is best avoided, since it might end up being identical to "+Inf".

    See also "nan", "isnan", "getpayload", and "issignaling".

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

    Returns "undef" on failure.

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

"setuid"
    Sets the real user identifier and the effective user identifier for this process. Similar to assigning a value to the Perl's builtin $< variable, see "$UID" in perlvar, except that the latter will change only the real user identifier.

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

    Synopsis:

            sigaction(signal, action, oldaction = 0)

    Returns "undef" on failure. The "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 constants for specific "code" values can be imported individually or using the ":signal_h_si_code" tag, since Perl v5.24.

    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
        addr        address of faulting instruction or memory
                    reference for SIGILL, SIGFPE, SIGSEGV or SIGBUS

    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 "sigaction" and possibly also "siginfo" documentation.

"siglongjmp"
    Not implemented. siglongjmp() is C-specific: use "die" in perlfunc instead.

"signbit"
    Returns zero for positive arguments, non-zero for negative arguments [C99]. Added in Perl v5.22.

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

    Synopsis:

            sigpending(sigset)

    Returns "undef" on failure.

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

    Synopsis:

            sigprocmask(how, sigset, oldsigset = 0)

    Returns "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.

"sigsetjmp"
    Not implemented. sigsetjmp() is C-specific: use "eval {}" instead, see "eval" in perlfunc.

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

    Synopsis:

            sigsuspend(signal_mask)

    Returns "undef" on failure.

"sin"
    This is identical to Perl's builtin sin() function, for returning the sine of its numerical argument -- except that POSIX::sin() must be provided with an explicit value (rather than relying on an implicit $_):

        $sine = POSIX::sin(3);    # good

        $sine = POSIX::sin();     # throws exception

    See "sin" in perlfunc; see also Math::Trig.

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

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

"sprintf"
    This is similar to Perl's builtin sprintf() function for returning a string that has the arguments formatted as requested, see "sprintf" in perlfunc.

"sqrt"
    This is identical to Perl's builtin sqrt() function for returning the square root of the numerical argument -- except that POSIX::sqrt() must be provided with an explicit value (rather than relying on an implicit $_):

        $square_root = POSIX::sqrt(3);    # good

        $square_root = POSIX::sqrt();     # throws exception

    See "sqrt" in perlfunc.

"srand"
    Give a seed the pseudorandom number generator, see "srand" in perlfunc.

"sscanf"
    Not implemented. sscanf() is C-specific, use regular expressions instead, see perlre.

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

"strcat"
    Not implemented. strcat() is C-specific, use ".=" instead, see perlop.

"strchr"
    Not implemented. strchr() is C-specific, see "index" in perlfunc instead.

"strcmp"
    Not implemented. strcmp() is C-specific, use "eq" or "cmp" instead, see perlop.

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

    Beware that in a UTF-8 locale, anything you pass to this function must be in UTF-8; and when not in a UTF-8 locale, anything passed must not be UTF-8 encoded.

    Note also that it doesn't make sense for a string to be encoded in one locale (say, ISO-8859-6, Arabic) and to collate it based on another (like ISO-8859-7, Greek). The results will be essentially meaningless.

"strcpy"
    Not implemented. strcpy() is C-specific, use "=" instead, see perlop.

"strcspn"
    Not implemented. strcspn() is C-specific, use regular expressions instead, see perlre.

"strerror"
    Returns the error string for the specified errno. Identical to the string form of $!, see "$ERRNO" in perlvar.

"strftime"
    Convert date and time information to string based on the current underlying locale of the program. Returns the string in a mortalized SV; set to an empty string on error.

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

    The "wday" and "yday" parameters are both ignored. Their values are always determinable from the other parameters.

    More details on the behavior and the specification of the other parameters are described in "sv_strftime_ints" in perlapi.

"strlen"
    Not implemented. strlen() is C-specific, use length() instead, see "length" in perlfunc.

"strncat"
    Not implemented. strncat() is C-specific, use ".=" instead, see perlop.

"strncmp"
    Not implemented. strncmp() is C-specific, use "eq" instead, see perlop.

"strncpy"
    Not implemented. strncpy() is C-specific, use "=" instead, see perlop.

"strpbrk"
    Not implemented. strpbrk() is C-specific, use regular expressions instead, see perlre.

"strrchr"
    Not implemented. strrchr() is C-specific, see "rindex" in perlfunc instead.

"strspn"
    Not implemented. strspn() is C-specific, use regular expressions instead, see perlre.

"strstr"
    This is identical to Perl's builtin index() function, see "index" in perlfunc.

"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" respects any POSIX setlocale() "LC_NUMERIC" settings, regardless of whether or not it is called from Perl code that is within the scope of "use locale". Prior to Perl 5.28, or when operating in a non thread-safe environment, it should not be used in a threaded application unless it's certain that the underlying locale is C or POSIX. This is because it otherwise changes the locale, which globally affects all threads simultaneously.

    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.

"strtok"
    Not implemented. strtok() is C-specific, use regular expressions instead, see perlre, or "split" in perlfunc.

"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 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.

"strtold"
    Like "strtod" but for long doubles. Defined only if the system supports long doubles.

"strtoul"
    String to unsigned (long) integer translation. strtoul() is identical to strtol() except that strtoul() only parses unsigned integers. See "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.

"strxfrm"
    String transformation. Returns the transformed string.

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

    Used with "eq" or "cmp" as an alternative to "strcoll".

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

    Unlike the libc "strxfrm", this allows NUL characters in the input $src.

    It doesn't make sense for a string to be encoded in one locale (say, ISO-8859-6, Arabic) and to collate it based on another (like ISO-8859-7, Greek). Perl assumes that the current "LC_CTYPE" locale correctly represents the encoding of $src, and ignores the value of "LC_COLLATE".

"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 "undef" on failure.

"system"
    This is identical to Perl's builtin system() function, see "system" in perlfunc.

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

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

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

    Returns "undef" on failure.

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

    Returns "undef" on failure.

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

    Returns "undef" on failure.

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

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

    Returns "undef" on failure.

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

    Returns "undef" on failure.

"tgamma"
    The Gamma function [C99]. Added in Perl v5.22.

    See also "lgamma".

"time"
    This is identical to Perl's builtin time() function for returning the number of seconds since the epoch (whatever it is for the system), see "time" in perlfunc.

"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 times() function returns four values, measured in seconds.

"tmpfile"
    Not implemented. Use method IO::File::new_tmpfile() instead, or see File::Temp.

"tmpnam"
    For security reasons, which are probably detailed in your system's documentation for the C library tmpnam() function, this interface is no longer available since Perl v5.26; instead use File::Temp.

"tolower"
    This function has been removed as of Perl v5.26. This is identical to the C function, except that it can apply to a single character or to a whole string, and currently operates as if the locale always is "C". Consider using the lc() function, see "lc" in perlfunc, see "lc" in perlfunc, or the equivalent "\L" operator inside doublequotish strings.

"toupper"
    This function has been removed as of Perl v5.26. This is similar to the C function, except that it can apply to a single character or to a whole string, and currently operates as if the locale always is "C". Consider using the uc() function, see "uc" in perlfunc, or the equivalent "\U" operator inside doublequotish strings.

"trunc"
    Returns the integer toward zero from the argument [C99]. Added in Perl v5.22.

    See also "ceil", "floor", and "round".

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

"tzname"
    Retrieves the time conversion information from the "tzname" variable.

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

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

"umask"
    This is identical to Perl's builtin umask() function for setting (and querying) the file creation permission mask -- except that POSIX::umask() must be provided with an explicit value (rather than relying on an implicit $_):

        $current = umask();                 # good

        $now  = POSIX::umask($current);     # good

        $now  = POSIX::umask();             # throws exception

    See "umask" in perlfunc.

"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 $sysname might be the name of the operating system, the $nodename might be the name of the host, the $release might be the (major) release number of the operating system, the $version might be the (minor) release number of the operating system, and the $machine might be a hardware identifier. Maybe.

"ungetc"
    Not implemented. Use method IO::Handle::ungetc() instead.

"unlink"
    This is identical to Perl's builtin unlink() function for removing files, see "unlink" in perlfunc.

"utime"
    This is identical to Perl's builtin utime() function for changing the time stamps of files and directories, see "utime" in perlfunc.

"vfprintf"
    Not implemented. vfprintf() is C-specific, see "printf" in perlfunc instead.

"vprintf"
    Not implemented. vprintf() is C-specific, see "printf" in perlfunc instead.

"vsprintf"
    Not implemented. vsprintf() is C-specific, see "sprintf" in perlfunc instead.

"wait"
    This is identical to Perl's builtin wait() function, see "wait" in perlfunc.

"waitpid"
    Wait for a child process to change state. This is identical to Perl's builtin waitpid() function, see "waitpid" in perlfunc.

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

    See "mblen".

"wctomb"
    This is the same as the C function wctomb() on unthreaded perls. On threaded perls, it transparently (almost) substitutes the more thread-safe "wcrtomb(3)", if available, instead of "wctomb".

    Core Perl does not have any support for wide and multibyte locales, except Unicode UTF-8 locales. This function, in conjunction with "mblen" and "mbtowc" may be used to roll your own decoding/encoding of other types of multi-byte locales.

    Use "undef" as the first parameter to this function to get the effect of passing NULL as the first parameter to "wctomb". This ignores the second parameter, and resets any shift state to its initial value. The return value is undefined if "wcrtomb" was substituted, so you should never rely on it.

    When the first parameter is a scalar, the code point contained in the scalar second parameter is converted into a multi-byte string and stored into the first parameter scalar. This is based on the locale that currently underlies the program, regardless of whether or not the function is called from Perl code that is within the scope of "use locale". The return value is the number of bytes stored; or negative if the code point isn't representable in the current locale. Perl makes no attempt at hiding from your code any differences in the "errno" setting between "wctomb" and "wcrtomb". It does set "errno" to 0 before calling them.

"write"
    Write to a file. This uses file descriptors such as those obtained by calling "POSIX::open".

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

    Returns "undef" on failure.

    See also "syswrite" in perlfunc.

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 );

    Throws an error if any of the signals supplied cannot be added to the set.

"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"

RESOURCE CONSTANTS
Imported with the ":sys_resource_h" tag.

Constants
    Added in Perl v5.28:

    "PRIO_PROCESS" "PRIO_PGRP" "PRIO_USER"

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"

    Added in Perl v5.22:

    "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"

    Added in Perl v5.24:

    "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_ISLNK" "S_ISREG" "S_ISSOCK"

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
    Added in Perl v5.24:

    "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"