NAME¶

POSIX - Perl interface to IEEE Std 1003.1

SYNOPSIS¶

    use POSIX ();
    use POSIX qw(setsid);
    use POSIX qw(:errno_h :fcntl_h);
    printf "EINTR is %d\n", EINTR;
    $sess_id = POSIX::setsid();
    $fd = POSIX::open($path, O_CREAT|O_EXCL|O_WRONLY, 0644);
        # note: that's a filedescriptor, *NOT* a filehandle

DESCRIPTION¶

The POSIX module permits you to access all (or nearly all) the standard POSIX 1003.1 identifiers. Many of these identifiers have been given Perl-ish interfaces.

This document gives a condensed list of the features available in the POSIX module. Consult your operating system's manpages for general information on most features. Consult perlfunc for functions which are noted as being identical 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 $min = POSIX::fmax($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.

"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 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 (C89, 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.

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.

"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 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¶

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_ISREG"

STDLIB¶

Constants

"EXIT_FAILURE" "EXIT_SUCCESS" "MB_CUR_MAX" "RAND_MAX"

STDIO¶

Constants

"BUFSIZ" "EOF" "FILENAME_MAX" "L_ctermid" "L_cuserid" "TMP_MAX"

TIME¶

Constants

"CLK_TCK" "CLOCKS_PER_SEC"

UNISTD¶

Constants

"R_OK" "SEEK_CUR" "SEEK_END" "SEEK_SET" "STDIN_FILENO" "STDOUT_FILENO" "STDERR_FILENO" "W_OK" "X_OK"

WAIT¶

Constants

"WNOHANG" "WUNTRACED"

Macros

"WIFEXITED" "WEXITSTATUS" "WIFSIGNALED" "WTERMSIG" "WIFSTOPPED" "WSTOPSIG"

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"