Manual Reference Pages  - POSIX (3pm)

NAME

POSIX - Perl interface to IEEE Std 1003.1

CONTENTS

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.

Everything is exported by default with the exception of any POSIX functions with the same name as a built-in Perl function, such as abs, alarm, rmdir, write, etc.., which will be exported only if you ask for them explicitly. This is an unfortunate backwards compatibility feature. You can stop the exporting by saying use POSIX () and then use the fully qualified names (ie. POSIX::SEEK_END).

This document gives a condensed list of the features available in the POSIX module. Consult your operating system’s manpages for general information on most features. Consult perlfunc for functions which are noted as being identical to Perl’s builtin functions.

The first section describes POSIX functions from the 1003.1 specification. The second section describes some classes for signal objects, TTY objects, and other miscellaneous objects. The remaining sections list various constants and macros in an organization which roughly follows IEEE Std 1003.1b-1993.

NOTE

The POSIX module is probably the most complex Perl module supplied with the standard distribution. It incorporates autoloading, namespace games, and dynamic loading of code that’s in Perl, C, or both. It’s a great source of wisdom.

CAVEATS

A few functions are not implemented because they are C specific. If you attempt to call these, they will print a message telling you that they aren’t implemented, and suggest using the Perl equivalent should one exist. For example, trying to access the setjmp() call will elicit the message setjmp() is C-specific: use eval {} instead.

Furthermore, some evil vendors will claim 1003.1 compliance, but in fact are not so: they will not pass the PCTS (POSIX Compliance Test Suites). For example, one vendor may not define EDEADLK, or the semantics of the errno values set by open(2) might not be quite right. Perl does not attempt to verify POSIX compliance. That means you can currently successfully say use POSIX, and then later in your program you find that your vendor has been lax and there’s no usable ICANON macro after all. This could be construed to be a bug.

FUNCTIONS

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

Note that when using threads and in Linux this is not a good way to exit a thread because in Linux processes and threads are kind of the same thing (Note: while this is the situation in early 2003 there are projects under way to have threads with more POSIXly semantics in Linux). If you want not to return from a thread, detach the thread.

abort This is identical to the C function abort(). It terminates the process with a SIGABRT signal unless caught by a signal handler or if the handler does not return normally (it e.g. does a longjmp).
abs This is identical to Perl’s builtin abs() function, returning the absolute value of its numerical argument.
access Determines the accessibility of a file.



        if( POSIX::access( "/", &POSIX::R_OK ) ){
                print "have read permission\n";
        }



Returns undef on failure. Note: do not use access() for security purposes. Between the access() call and the operation you are preparing for the permissions might change: a classic race condition.

acos This is identical to the C function acos(), returning the arcus cosine of its numerical argument. See also Math::Trig.
alarm This is identical to Perl’s builtin alarm() function, either for arming or disarming the SIGARLM timer.
asctime This is identical to the C function asctime(). It returns a string of the form



        "Fri Jun  2 18:22:13 2000\n\0"



and it is called thusly



        $asctime = asctime($sec, $min, $hour, $mday, $mon, $year,
                           $wday, $yday, $isdst);



The $mon is zero-based: January equals 0. The $year is 1900-based: 2001 equals 101. The $wday, $yday, and $isdst default to zero (and the first two are usually ignored anyway).

asin This is identical to the C function asin(), returning the arcus sine of its numerical argument. See also Math::Trig.
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.
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 atexit() is C-specific: use END {} instead, see perlsub.
atof atof() is C-specific. Perl converts strings to numbers transparently. If you need to force a scalar to a number, add a zero to it.
atoi atoi() is C-specific. Perl converts strings to numbers transparently. If you need to force a scalar to a number, add a zero to it. If you need to have just the integer part, see int in perlfunc.
atol atol() is C-specific. Perl converts strings to numbers transparently. If you need to force a scalar to a number, add a zero to it. If you need to have just the integer part, see int in perlfunc.
bsearch bsearch() not supplied. For doing binary search on wordlists, see Search::Dict.
calloc calloc() is C-specific. Perl does memory management transparently.
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.
chmod This is identical to Perl’s builtin chmod() function, allowing one to change file and directory permissions, see chmod in perlfunc.
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 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.
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 Get the login name of the owner of the current process.



        $name = POSIX::cuserid();



difftime This is identical to the C function difftime(), for returning the time difference (in seconds) between two times (as returned by time()), see time.
div 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.

errno Returns the value of errno.



        $errno = POSIX::errno();



This identical to the numerical values of the $!, see $ERRNO in perlvar.

execl execl() is C-specific, see exec in perlfunc.
execle execle() is C-specific, see exec in perlfunc.
execlp execlp() is C-specific, see exec in perlfunc.
execv execv() is C-specific, see exec in perlfunc.
execve execve() is C-specific, see exec in perlfunc.
execvp 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.
fabs This is identical to Perl’s builtin abs() function for returning the absolute value of the numerical argument, see abs in perlfunc.
fclose 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 Use method IO::Handle::new_from_fd() instead, or see open in perlfunc.
feof Use method IO::Handle::eof() instead, or see eof in perlfunc.
ferror Use method IO::Handle::error() instead.
fflush Use method IO::Handle::flush() instead. See also $OUTPUT_AUTOFLUSH in perlvar.
fgetc Use method IO::Handle::getc() instead, or see read in perlfunc.
fgetpos Use method IO::Seekable::getpos() instead, or see seek in L.
fgets Use method IO::Handle::gets() instead. Similar to <>, also known as readline in perlfunc.
fileno 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.
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 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.

fprintf fprintf() is C-specific, see printf in perlfunc instead.
fputc fputc() is C-specific, see print in perlfunc instead.
fputs fputs() is C-specific, see print in perlfunc instead.
fread fread() is C-specific, see read in perlfunc instead.
free free() is C-specific. Perl does memory management transparently.
freopen 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 fscanf() is C-specific, use <> and regular expressions instead.
fseek Use method IO::Seekable::seek() instead, or see seek in perlfunc.
fsetpos 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 Use method IO::Handle::sync() instead.
ftell Use method IO::Seekable::tell() instead, or see tell in perlfunc.
fwrite 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.
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.
isalnum This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isalnum. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:alnum:]]/ construct instead, or possibly the /\w/ construct.
isalpha This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isalpha. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:alpha:]]/ construct instead.
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 is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered iscntrl. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:cntrl:]]/ construct instead.
isdigit This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isdigit (unlikely, but still possible). Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:digit:]]/ construct instead, or the /\d/ construct.
isgraph This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isgraph. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:graph:]]/ construct instead.
islower This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered islower. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:lower:]]/ construct instead. Do not use /[a-z]/.
isprint This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isprint. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:print:]]/ construct instead.
ispunct This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered ispunct. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:punct:]]/ construct instead.
isspace This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isspace. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:space:]]/ construct instead, or the /\s/ construct. (Note that /\s/ and /[[:space:]]/ are slightly different in that /[[:space:]]/ can normally match a vertical tab, while /\s/ does not.)
isupper This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isupper. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:upper:]]/ construct instead. Do not use /[A-Z]/.
isxdigit This is identical to the C function, except that it can apply to a single character or to a whole string. Note that locale settings may affect what characters are considered isxdigit (unlikely, but still possible). Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the /[[:xdigit:]]/ construct instead, or simply /[0-9a-f]/i.
kill This is identical to Perl’s builtin kill() function for sending signals to processes (often to terminate them), see kill in perlfunc.
labs (For returning absolute values of long integers.) labs() is C-specific, see abs in perlfunc instead.
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 (For computing dividends of long integers.) ldiv() is C-specific, use / and int() instead.
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 current locale formatting values.

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



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



localtime This is identical to Perl’s builtin localtime() function for converting seconds since the epoch to a date see localtime in perlfunc.
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 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.

malloc malloc() is C-specific. Perl does memory management transparently.
mblen This is identical to the C function mblen(). Perl does not have any support for the wide and multibyte characters of the C standards, so this might be a rather useless function.
mbstowcs This is identical to the C function mbstowcs(). Perl does not have any support for the wide and multibyte characters of the C standards, so this might be a rather useless function.
mbtowc This is identical to the C function mbtowc(). Perl does not have any support for the wide and multibyte characters of the C standards, so this might be a rather useless function.
memchr memchr() is C-specific, see index in perlfunc instead.
memcmp memcmp() is C-specific, use eq instead, see perlop.
memcpy memcpy() is C-specific, use =, see perlop, or see substr in perlfunc.
memmove memmove() is C-specific, use =, see perlop, or see substr in perlfunc.
memset 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.

mktime Convert date/time info to a calendar time.

Synopsis:



        mktime(sec, min, hour, mday, mon, year, wday = 0, yday = 0, isdst = 0)



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 );



nice This is similar to the C function nice(), for changing the scheduling preference of the current process. Positive arguments mean more polite process, negative values more needy process. Normal user processes can only be more polite.

Returns undef on failure.

offsetof 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 putc() is C-specific, see print in perlfunc instead.
putchar putchar() is C-specific, see print in perlfunc instead.
puts puts() is C-specific, see print in perlfunc instead.
qsort 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 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 realloc() is C-specific. Perl does memory management transparently.
remove This is identical to Perl’s builtin unlink() function for removing files, see unlink in perlfunc.
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.
rmdir This is identical to Perl’s builtin rmdir() function for removing (empty) directories, see rmdir in perlfunc.
scanf 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 $GID 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 setjmp() is C-specific: use eval {} instead, see eval in perlfunc.
setlocale Modifies and queries program’s locale. The following examples assume



        use POSIX qw(setlocale LC_ALL LC_CTYPE);



has been issued.

The following will set the traditional UNIX system locale behavior (the second argument "C").



        $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 systems 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_ALL, "es_AR.ISO8859-1" );



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. Consult your system’s sigaction manpage for details.

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.

siglongjmp siglongjmp() is C-specific: use die in perlfunc instead.
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.

sigsetjmp 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 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 strcat() is C-specific, use .= instead, see perlop.
strchr strchr() is C-specific, see index in perlfunc instead.
strcmp 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.
strcpy strcpy() is C-specific, use = instead, see perlop.
strcspn 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 the $!, 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 strlen() is C-specific, use length() instead, see length in perlfunc.
strncat strncat() is C-specific, use .= instead, see perlop.
strncmp strncmp() is C-specific, use eq instead, see perlop.
strncpy strncpy() is C-specific, use = instead, see perlop.
strpbrk strpbrk() is C-specific, use regular expressions instead, see perlre.
strrchr strrchr() is C-specific, see rindex in perlfunc instead.
strspn 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 should respect any POSIX setlocale() settings.

To parse a string $str as a floating point number use



    $! = 0;
    ($num, $n_unparsed) = POSIX::strtod($str);



The second returned item and $! can be used to check for valid input:



    if (($str eq ’’) || ($n_unparsed != 0) || $!) {
        die "Non-numeric input $str" . ($! ? ": $!\n" : "\n");
    }



When called in a scalar context strtod returns the parsed number.

strtok 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.

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 in conjunction with the strcoll() function, see strcoll.

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

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.

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 Use method IO::File::new_tmpfile() instead, or see File::Temp.
tmpnam Returns a name for a temporary file.



        $tmpfile = POSIX::tmpnam();



For security reasons, which are probably detailed in your system’s documentation for the C library tmpnam() function, this interface should not be used; instead see File::Temp.

tolower This is identical to the C function, except that it can apply to a single character or to a whole string. Consider using the lc() function, see lc in perlfunc, or the equivalent \L operator inside doublequotish strings.
toupper This is identical to the C function, except that it can apply to a single character or to a whole string. Consider using the uc() function, see uc in perlfunc, or the equivalent \U operator inside doublequotish strings.
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 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 vfprintf() is C-specific, see printf in perlfunc instead.
vprintf vprintf() is C-specific, see printf in perlfunc instead.
vsprintf 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";



wcstombs This is identical to the C function wcstombs(). Perl does not have any support for the wide and multibyte characters of the C standards, so this might be a rather useless function.
wctomb This is identical to the C function wctomb(). Perl does not have any support for the wide and multibyte characters of the C standards, so this might be a rather useless function.
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( $b, $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 fully-qualified name of a sub which is a signal-handler. 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( \&main::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::SigSet

new Create a new SigSet object. This object will be destroyed automatically when it is no longer needed. Arguments may be supplied to initialize the set.

Create an empty set.



        $sigset = POSIX::SigSet->new;



Create a set with SIGUSR1.



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



addset Add a signal to a SigSet object.



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



Returns undef on failure.

delset Remove a signal from the SigSet object.



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



Returns undef on failure.

emptyset Initialize the SigSet object to be empty.



        $sigset->emptyset();



Returns undef on failure.

fillset Initialize the SigSet object to include all signals.



        $sigset->fillset();



Returns undef on failure.

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



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



POSIX::Termios

new Create a new Termios object. This object will be destroyed automatically when it is no longer needed. A Termios object corresponds to the termios C struct. new() mallocs a new one, getattr() fills it from a file descriptor, and setattr() sets a file descriptor’s parameters to match Termios’ contents.



        $termios = POSIX::Termios->new;



getattr Get terminal control attributes.

Obtain the attributes for stdin.



        $termios->getattr()



Obtain the attributes for stdout.



        $termios->getattr( 1 )



Returns undef on failure.

getcc Retrieve a value from the c_cc field of a termios object. The c_cc field is an array so an index must be specified.



        $c_cc[1] = $termios->getcc(1);



getcflag Retrieve the c_cflag field of a termios object.



        $c_cflag = $termios->getcflag;



getiflag Retrieve the c_iflag field of a termios object.



        $c_iflag = $termios->getiflag;



getispeed Retrieve the input baud rate.



        $ispeed = $termios->getispeed;



getlflag Retrieve the c_lflag field of a termios object.



        $c_lflag = $termios->getlflag;



getoflag Retrieve the c_oflag field of a termios object.



        $c_oflag = $termios->getoflag;



getospeed Retrieve the output baud rate.



        $ospeed = $termios->getospeed;



setattr Set terminal control attributes.

Set attributes immediately for stdout.



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



Returns undef on failure.

setcc Set a value in the c_cc field of a termios object. The c_cc field is an array so an index must be specified.



        $termios->setcc( &POSIX::VEOF, 1 );



setcflag Set the c_cflag field of a termios object.



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



setiflag Set the c_iflag field of a termios object.



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



setispeed Set the input baud rate.



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



Returns undef on failure.

setlflag Set the c_lflag field of a termios object.



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



setoflag Set the c_oflag field of a termios object.



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



setospeed Set the output baud rate.



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



Returns undef on failure.

Baud rate values B38400 B75 B200 B134 B300 B1800 B150 B0 B19200 B1200 B9600 B600 B4800 B50 B2400 B110
Terminal interface values TCSADRAIN TCSANOW TCOON TCIOFLUSH TCOFLUSH TCION TCIFLUSH TCSAFLUSH TCIOFF TCOOFF
c_cc field values VEOF VEOL VERASE VINTR VKILL VQUIT VSUSP VSTART VSTOP VMIN VTIME NCCS
c_cflag field values CLOCAL CREAD CSIZE CS5 CS6 CS7 CS8 CSTOPB HUPCL PARENB PARODD
c_iflag field values BRKINT ICRNL IGNBRK IGNCR IGNPAR INLCR INPCK ISTRIP IXOFF IXON PARMRK
c_lflag field values ECHO ECHOE ECHOK ECHONL ICANON IEXTEN ISIG NOFLSH TOSTOP
c_oflag field values OPOST

PATHNAME CONSTANTS

Constants _PC_CHOWN_RESTRICTED _PC_LINK_MAX _PC_MAX_CANON _PC_MAX_INPUT _PC_NAME_MAX _PC_NO_TRUNC _PC_PATH_MAX _PC_PIPE_BUF _PC_VDISABLE

POSIX CONSTANTS

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

SYSTEM CONFIGURATION

Constants _SC_ARG_MAX _SC_CHILD_MAX _SC_CLK_TCK _SC_JOB_CONTROL _SC_NGROUPS_MAX _SC_OPEN_MAX _SC_PAGESIZE _SC_SAVED_IDS _SC_STREAM_MAX _SC_TZNAME_MAX _SC_VERSION

ERRNO

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

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

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

MATH

Constants HUGE_VAL

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

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 L_tmpname 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($?) returns true if the child process exited normally (exit() or by falling off the end of main())
WEXITSTATUS WEXITSTATUS($?) returns the normal exit status of the child process (only meaningful if WIFEXITED($?) is true)
WIFSIGNALED WIFSIGNALED($?) returns true if the child process terminated because of a signal
WTERMSIG WTERMSIG($?) returns the signal the child process terminated for (only meaningful if WIFSIGNALED($?) is true)
WIFSTOPPED WIFSTOPPED($?) returns true if the child process is currently stopped (can happen only if you specified the WUNTRACED flag to waitpid())
WSTOPSIG WSTOPSIG($?) returns the signal the child process was stopped for (only meaningful if WIFSTOPPED($?) is true)


perl v5.8.8 POSIX (3pm) 2001-09-21
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