perldoc > POSIX(1)

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, 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, 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, see "abs" in perlfunc.

    "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
            omittted 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, returning the natural (*e*-based)
            logarithm of the numerical argument, 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 the
            numerical argument, 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, 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. Returns the string.

            Synopsis:

                    strftime(fmt, sec, min, hour, mday, mon, year,
                             wday = -1, yday = -1, 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 strftime() manpage for details about these and the other arguments.

            If you want your code to be portable, your format ("fmt") argument should use only the
            conversion specifiers defined by the ANSI C standard (C99, to play safe). These are
            "aAbBcdHIjmMpSUwWxXyYZ%". But even then, the results of some of the conversion
            specifiers are non-portable. For example, the specifiers "aAbBcpZ" change according to
            the locale settings of the user, and both how to set locales (the locale names) and what
            output to expect are non-standard. The specifier "c" changes according to the timezone
            settings of the user and the timezone computation rules of the operating system. The "Z"
            specifier is notoriously unportable since the names of timezones are non-standard.
            Sticking to the numeric specifiers is the safest route.

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

            The string for Tuesday, December 12, 1995.

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

    "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, 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"

POSIX(1) □✕
NAME SYNOPSIS DESCRIPTION CAVEATS FUNCTIONS CLASSES PATHNAME CONSTANTS POSIX CONSTANTS RESOURCE CONSTANTS SYSTEM CONFIGURATION ERRNO FCNTL FLOAT FLOATING-POINT ENVIRONMENT LIMITS LOCALE MATH SIGNAL STAT STDLIB STDIO TIME UNISTD WAIT WINSOCK

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