POSIX - Perl interface to IEEE Std 1003.1
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 filehandleThe 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.
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.
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.
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.
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).
This is identical to Perl's builtin abs() function, returning the absolute value of its numerical argument.
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.
This is identical to the C function acos(), returning the arcus cosine of its numerical argument. See also Math::Trig.
This is identical to Perl's builtin alarm() function, either for arming or disarming the SIGARLM timer.
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.
This is identical to the C function asin(), returning the arcus sine of its numerical argument. See also Math::Trig.
Unimplemented, but you can use "die" in perlfunc and the Carp module to achieve similar things.
This is identical to the C function atan(), returning the arcus tangent of its numerical argument. See also Math::Trig.
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() is C-specific: use END {} instead, see perlsub.
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() 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() 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() not supplied. For doing binary search on wordlists, see Search::Dict.
calloc() is C-specific. Perl does memory management transparently.
This is identical to the C function ceil(), returning the smallest integer value greater than or equal to the given numerical argument.
This is identical to Perl's builtin chdir() function, allowing one to change the working (default) directory, see "chdir" in perlfunc.
This is identical to Perl's builtin chmod() function, allowing one to change file and directory permissions, see "chmod" in perlfunc.
This is identical to Perl's builtin chown() function, allowing one to change file and directory owners and groups, see "chown" in perlfunc.
Use the method IO::Handle::clearerr() instead, to reset the error state (if any) and EOF state (if any) of the given stream.
This is identical to the C function clock(), returning the amount of spent processor time in microseconds.
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.
This is identical to Perl's builtin closedir() function for closing a directory handle, see "closedir" in perlfunc.
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.
This is identical to the C function cosh(), for returning the hyperbolic cosine of its numeric argument. See also Math::Trig.
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.
Generates the path name for the controlling terminal.
$path = POSIX::ctermid();This is identical to the C function ctime() and equivalent to asctime(localtime(...)), see "asctime" and "localtime".
Get the login name of the owner of the current process.
$name = POSIX::cuserid();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() is C-specific, use "int" in perlfunc on the usual / division and the modulus %.
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.
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.
Returns the value of errno.
$errno = POSIX::errno();This identical to the numerical values of the $!, see "$ERRNO" in perlvar.
execl() is C-specific, see "exec" in perlfunc.
execle() is C-specific, see "exec" in perlfunc.
execlp() is C-specific, see "exec" in perlfunc.
execv() is C-specific, see "exec" in perlfunc.
execve() is C-specific, see "exec" in perlfunc.
execvp() is C-specific, see "exec" in perlfunc.
This is identical to Perl's builtin exit() function for exiting the program, see "exit" in perlfunc.
This is identical to Perl's builtin exp() function for returning the exponent (e-based) of the numerical argument, see "exp" in perlfunc.
This is identical to Perl's builtin abs() function for returning the absolute value of the numerical argument, see "abs" in perlfunc.
Use method IO::Handle::close() instead, or see "close" in perlfunc.
This is identical to Perl's builtin fcntl() function, see "fcntl" in perlfunc.
Use method IO::Handle::new_from_fd() instead, or see "open" in perlfunc.
Use method IO::Handle::eof() instead, or see "eof" in perlfunc.
Use method IO::Handle::error() instead.
Use method IO::Handle::flush() instead. See also "$OUTPUT_AUTOFLUSH" in perlvar.
Use method IO::Handle::getc() instead, or see "read" in perlfunc.
Use method IO::Seekable::getpos() instead, or see "seek" in L.
Use method IO::Handle::gets() instead. Similar to <>, also known as "readline" in perlfunc.
Use method IO::Handle::fileno() instead, or see "fileno" in perlfunc.
This is identical to the C function floor(), returning the largest integer value less than or equal to the numerical argument.
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.
Use method IO::File::open() instead, or see "open" in perlfunc.
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.
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( $fd, &POSIX::_PC_PATH_MAX );Returns undef on failure.
fprintf() is C-specific, see "printf" in perlfunc instead.
fputc() is C-specific, see "print" in perlfunc instead.
fputs() is C-specific, see "print" in perlfunc instead.
fread() is C-specific, see "read" in perlfunc instead.
free() is C-specific. Perl does memory management transparently.
freopen() is C-specific, see "open" in perlfunc instead.
Return the mantissa and exponent of a floating-point number.
($mantissa, $exponent) = POSIX::frexp( 1.234e56 );fscanf() is C-specific, use <> and regular expressions instead.
Use method IO::Seekable::seek() instead, or see "seek" in perlfunc.
Use method IO::Seekable::setpos() instead, or seek "seek" in perlfunc.
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 );Use method IO::Handle::sync() instead.
Use method IO::Seekable::tell() instead, or see "tell" in perlfunc.
fwrite() is C-specific, see "print" in perlfunc instead.
This is identical to Perl's builtin getc() function, see "getc" in perlfunc.
Returns one character from STDIN. Identical to Perl's getc(), see "getc" in perlfunc.
Returns the name of the current working directory. See also Cwd.
Returns the effective group identifier. Similar to Perl' s builtin variable $(, see "$EGID" in perlvar.
Returns the value of the specified environment variable. The same information is available through the %ENV array.
Returns the effective user identifier. Identical to Perl's builtin $> variable, see "$EUID" in perlvar.
Returns the user's real group identifier. Similar to Perl's builtin variable $), see "$GID" in perlvar.
This is identical to Perl's builtin getgrgid() function for returning group entries by group identifiers, see "getgrgid" in perlfunc.
This is identical to Perl's builtin getgrnam() function for returning group entries by group names, see "getgrnam" in perlfunc.
Returns the ids of the user's supplementary groups. Similar to Perl's builtin variable $), see "$GID" in perlvar.
This is identical to Perl's builtin getlogin() function for returning the user name associated with the current session, see "getlogin" in perlfunc.
This is identical to Perl's builtin getpgrp() function for returning the process group identifier of the current process, see "getpgrp" in perlfunc.
Returns the process identifier. Identical to Perl's builtin variable $$, see "$PID" in perlvar.
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.
This is identical to Perl's builtin getpwnam() function for returning user entries by user names, see "getpwnam" in perlfunc.
This is identical to Perl's builtin getpwuid() function for returning user entries by user identifiers, see "getpwuid" in perlfunc.
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.
Returns the user's identifier. Identical to Perl's builtin $< variable, see "$UID" in perlvar.
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.
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.
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.
Returns a boolean indicating whether the specified filehandle is connected to a tty. Similar to the -t operator, see "-X" in perlfunc.
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.
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.
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.
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]/.
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.
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.
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.)
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]/.
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.
This is identical to Perl's builtin kill() function for sending signals to processes (often to terminate them), see "kill" in perlfunc.
(For returning absolute values of long integers.) labs() is C-specific, see "abs" in perlfunc instead.
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 an 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.
This is identical to the C function ldexp() for multiplying floating point numbers with powers of two.
$x_quadrupled = POSIX::ldexp($x, 2);(For computing dividends of long integers.) ldiv() is C-specific, use / and int() instead.
This is identical to Perl's builtin link() function for creating hard links into files, see "link" in perlfunc.
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";This is identical to Perl's builtin localtime() function for converting seconds since the epoch to a date see "localtime" in perlfunc.
This is identical to Perl's builtin log() function, returning the natural (e-based) logarithm of the numerical argument, see "log" in perlfunc.
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() is C-specific: use "die" in perlfunc instead.
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() is C-specific. Perl does memory management transparently.
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.
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.
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() is C-specific, see "index" in perlfunc instead.
memcmp() is C-specific, use eq instead, see perlop.
memcpy() is C-specific, use =, see perlop, or see "substr" in perlfunc.
memmove() is C-specific, use =, see perlop, or see "substr" in perlfunc.
memset() is C-specific, use x instead, see perlop.
This is identical to Perl's builtin mkdir() function for creating directories, see "mkdir" in perlfunc.
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.
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.
Return the integral and fractional parts of a floating-point number.
($fractional, $integral) = POSIX::modf( 3.14 );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() is C-specific, you probably want to see "pack" in perlfunc instead.
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.
Open a directory for reading.
$dir = POSIX::opendir( "/var" );
@files = POSIX::readdir( $dir );
POSIX::closedir( $dir );Returns undef on failure.
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.
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.
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.
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.
Computes $x raised to the power $exponent.
$ret = POSIX::pow( $x, $exponent );You can also use the ** operator, see perlop.
Formats and prints the specified arguments to STDOUT. See also "printf" in perlfunc.
putc() is C-specific, see "print" in perlfunc instead.
putchar() is C-specific, see "print" in perlfunc instead.
puts() is C-specific, see "print" in perlfunc instead.
qsort() is C-specific, see "sort" in perlfunc instead.
Sends the specified signal to the current process. See also "kill" in perlfunc and the $$ in "$PID" in perlvar.
rand() is non-portable, see "rand" in perlfunc instead.
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.
This is identical to Perl's builtin readdir() function for reading directory entries, see "readdir" in perlfunc.
realloc() is C-specific. Perl does memory management transparently.
This is identical to Perl's builtin unlink() function for removing files, see "unlink" in perlfunc.
This is identical to Perl's builtin rename() function for renaming files, see "rename" in perlfunc.
Seeks to the beginning of the file.
This is identical to Perl's builtin rewinddir() function for rewinding directory entry streams, see "rewinddir" in perlfunc.
This is identical to Perl's builtin rmdir() function for removing (empty) directories, see "rmdir" in perlfunc.
scanf() is C-specific, use <> and regular expressions instead, see perlre.
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() is C-specific: use eval {} instead, see "eval" in perlfunc.
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_COLLATE, "es_AR.ISO8859-1" );This is similar to the C function setpgid() for setting the process group identifier of the current process.
Returns undef on failure.
This is identical to the C function setsid() for setting the session identifier of the current process.
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.
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 kernelThe 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 SIGPOLLA 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() is C-specific: use "die" in perlfunc instead.
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.
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() is C-specific: use eval {} instead, see "eval" in perlfunc.
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.
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.
This is identical to the C function sinh() for returning the hyperbolic sine of the numerical argument. See also Math::Trig.
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.
This is similar to Perl's builtin sprintf() function for returning a string that has the arguments formatted as requested, see "sprintf" in perlfunc.
This is identical to Perl's builtin sqrt() function. for returning the square root of the numerical argument, see "sqrt" in perlfunc.
Give a seed the pseudorandom number generator, see "srand" in perlfunc.
sscanf() is C-specific, use regular expressions instead, see perlre.
This is identical to Perl's builtin stat() function for returning information about files and directories.
strcat() is C-specific, use .= instead, see perlop.
strchr() is C-specific, see "index" in perlfunc instead.
strcmp() is C-specific, use eq or cmp instead, see perlop.
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() is C-specific, use = instead, see perlop.
strcspn() is C-specific, use regular expressions instead, see perlre.
Returns the error string for the specified errno. Identical to the string form of the $!, see "$ERRNO" in perlvar.
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() is C-specific, use length() instead, see "length" in perlfunc.
strncat() is C-specific, use .= instead, see perlop.
strncmp() is C-specific, use eq instead, see perlop.
strncpy() is C-specific, use = instead, see perlop.
strpbrk() is C-specific, use regular expressions instead, see perlre.
strrchr() is C-specific, see "rindex" in perlfunc instead.
strspn() is C-specific, use regular expressions instead, see perlre.
This is identical to Perl's builtin index() function, see "index" in perlfunc.
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() is C-specific, use regular expressions instead, see perlre, or "split" in perlfunc.
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.
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.
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.
Retrieves values of system configurable variables.
The following will get the machine's clock speed.
$clock_ticks = POSIX::sysconf( &POSIX::_SC_CLK_TCK );Returns undef on failure.
This is identical to Perl's builtin system() function, see "system" in perlfunc.
This is identical to the C function tan(), returning the tangent of the numerical argument. See also Math::Trig.
This is identical to the C function tanh(), returning the hyperbolic tangent of the numerical argument. See also Math::Trig.
This is similar to the C function tcdrain() for draining the output queue of its argument stream.
Returns undef on failure.
This is similar to the C function tcflow() for controlling the flow of its argument stream.
Returns undef on failure.
This is similar to the C function tcflush() for flushing the I/O buffers of its argument stream.
Returns undef on failure.
This is identical to the C function tcgetpgrp() for returning the process group identifier of the foreground process group of the controlling terminal.
This is similar to the C function tcsendbreak() for sending a break on its argument stream.
Returns undef on failure.
This is similar to the C function tcsetpgrp() for setting the process group identifier of the foreground process group of the controlling terminal.
Returns undef on failure.
This is identical to Perl's builtin time() function for returning the number of seconds since the epoch (whatever it is for the system), see "time" in perlfunc.
The times() function returns elapsed realtime since some point in the past (such as system startup), user and system times for this process, and user and system times used by child processes. All times are returned in clock ticks.
($realtime, $user, $system, $cuser, $csystem) = POSIX::times();Note: Perl's builtin times() function returns four values, measured in seconds.
Use method IO::File::new_tmpfile() instead, or see File::Temp.
Returns a name for a temporary file.
$tmpfile = POSIX::tmpnam();For security reasons, which are probably detailed in your system's documentation for the C library tmpnam() function, this interface should not be used; instead see File::Temp.
This is identical to the C function, except that it can apply to a single character or to a whole string. Consider using the lc() function, see "lc" in perlfunc, or the equivalent \L operator inside doublequotish strings.
This is identical to the C function, except that it can apply to a single character or to a whole string. Consider using the uc() function, see "uc" in perlfunc, or the equivalent \U operator inside doublequotish strings.
This is identical to the C function ttyname() for returning the name of the current terminal.
Retrieves the time conversion information from the tzname variable.
POSIX::tzset();
($std, $dst) = POSIX::tzname();This is identical to the C function tzset() for setting the current timezone based on the environment variable TZ, to be used by ctime(), localtime(), mktime(), and strftime() functions.
This is identical to Perl's builtin umask() function for setting (and querying) the file creation permission mask, see "umask" in perlfunc.
Get name of current operating system.
($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.
Use method IO::Handle::ungetc() instead.
This is identical to Perl's builtin unlink() function for removing files, see "unlink" in perlfunc.
This is identical to Perl's builtin utime() function for changing the time stamps of files and directories, see "utime" in perlfunc.
vfprintf() is C-specific, see "printf" in perlfunc instead.
vprintf() is C-specific, see "printf" in perlfunc instead.
vsprintf() is C-specific, see "sprintf" in perlfunc instead.
This is identical to Perl's builtin wait() function, see "wait" in perlfunc.
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";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.
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 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.
Creates a new POSIX::SigAction object which corresponds to the C struct sigaction. This object will be destroyed automatically when it is no longer needed. The first parameter is the handler, a sub reference. The second parameter is a POSIX::SigSet object, it defaults to the empty set. The third parameter contains the sa_flags, it defaults to 0.
$sigset = POSIX::SigSet->new(SIGINT, SIGQUIT);
$sigaction = POSIX::SigAction->new( \&handler, $sigset, &POSIX::SA_NOCLDSTOP );This POSIX::SigAction object is intended for use with the POSIX::sigaction() function.
accessor functions to get/set the values of a SigAction object.
$sigset = $sigaction->mask;
$sigaction->flags(&POSIX::SA_RESTART);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
}A hash of the POSIX realtime signal handlers. It is an extension of the standard %SIG, the $POSIX::SIGRT{SIGRTMIN} is roughly equivalent to $SIG{SIGRTMIN}, but the right POSIX moves (see below) are made with the POSIX::SigSet and POSIX::sigaction instead of accessing the %SIG.
You can set the %POSIX::SIGRT elements to set the POSIX realtime signal handlers, use delete and exists on the elements, and use scalar on the %POSIX::SIGRT to find out how many POSIX realtime signals there are available (SIGRTMAX - SIGRTMIN + 1, the SIGRTMAX is a valid POSIX realtime signal).
Setting the %SIGRT elements is equivalent to calling this:
sub new {
my ($rtsig, $handler, $flags) = @_;
my $sigset = POSIX::SigSet($rtsig);
my $sigact = POSIX::SigAction->new($handler, $sigset, $flags);
sigaction($rtsig, $sigact);
}The flags default to zero, if you want something different you can either use local on $POSIX::SigRt::SIGACTION_FLAGS, or you can derive from POSIX::SigRt and define your own new() (the tied hash STORE method of the %SIGRT calls new($rtsig, $handler, $SIGACTION_FLAGS), where the $rtsig ranges from zero to SIGRTMAX - SIGRTMIN + 1).
Just as with any signal, you can use sigaction($rtsig, undef, $oa) to retrieve the installed signal handler (or, rather, the signal action).
NOTE: whether POSIX realtime signals really work in your system, or whether Perl has been compiled so that it works with them, is outside of this discussion.
Return the minimum POSIX realtime signal number available, or undef if no POSIX realtime signals are available.
Return the maximum POSIX realtime signal number available, or undef if no POSIX realtime signals are available.
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 );Add a signal to a SigSet object.
$sigset->addset( &POSIX::SIGUSR2 );Returns undef on failure.
Remove a signal from the SigSet object.
$sigset->delset( &POSIX::SIGUSR2 );Returns undef on failure.
Initialize the SigSet object to be empty.
$sigset->emptyset();Returns undef on failure.
Initialize the SigSet object to include all signals.
$sigset->fillset();Returns undef on failure.
Tests the SigSet object to see if it contains a specific signal.
if( $sigset->ismember( &POSIX::SIGUSR1 ) ){
print "contains SIGUSR1\n";
}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;Get terminal control attributes.
Obtain the attributes for stdin.
$termios->getattr( 0 ) # Recommended for clarity.
$termios->getattr()Obtain the attributes for stdout.
$termios->getattr( 1 )Returns undef on failure.
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);Retrieve the c_cflag field of a termios object.
$c_cflag = $termios->getcflag;Retrieve the c_iflag field of a termios object.
$c_iflag = $termios->getiflag;Retrieve the input baud rate.
$ispeed = $termios->getispeed;Retrieve the c_lflag field of a termios object.
$c_lflag = $termios->getlflag;Retrieve the c_oflag field of a termios object.
$c_oflag = $termios->getoflag;Retrieve the output baud rate.
$ospeed = $termios->getospeed;Set terminal control attributes.
Set attributes immediately for stdout.
$termios->setattr( 1, &POSIX::TCSANOW );Returns undef on failure.
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 );Set the c_cflag field of a termios object.
$termios->setcflag( $c_cflag | &POSIX::CLOCAL );Set the c_iflag field of a termios object.
$termios->setiflag( $c_iflag | &POSIX::BRKINT );Set the input baud rate.
$termios->setispeed( &POSIX::B9600 );Returns undef on failure.
Set the c_lflag field of a termios object.
$termios->setlflag( $c_lflag | &POSIX::ECHO );Set the c_oflag field of a termios object.
$termios->setoflag( $c_oflag | &POSIX::OPOST );Set the output baud rate.
$termios->setospeed( &POSIX::B9600 );Returns undef on failure.
B38400 B75 B200 B134 B300 B1800 B150 B0 B19200 B1200 B9600 B600 B4800 B50 B2400 B110
TCSADRAIN TCSANOW TCOON TCIOFLUSH TCOFLUSH TCION TCIFLUSH TCSAFLUSH TCIOFF TCOOFF
VEOF VEOL VERASE VINTR VKILL VQUIT VSUSP VSTART VSTOP VMIN VTIME NCCS
CLOCAL CREAD CSIZE CS5 CS6 CS7 CS8 CSTOPB HUPCL PARENB PARODD
BRKINT ICRNL IGNBRK IGNCR IGNPAR INLCR INPCK ISTRIP IXOFF IXON PARMRK
ECHO ECHOE ECHOK ECHONL ICANON IEXTEN ISIG NOFLSH TOSTOP
OPOST
_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_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
_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
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
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
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
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
LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME
HUGE_VAL
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
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
S_ISBLK S_ISCHR S_ISDIR S_ISFIFO S_ISREG
EXIT_FAILURE EXIT_SUCCESS MB_CUR_MAX RAND_MAX
BUFSIZ EOF FILENAME_MAX L_ctermid L_cuserid L_tmpname TMP_MAX
CLK_TCK CLOCKS_PER_SEC
R_OK SEEK_CUR SEEK_END SEEK_SET STDIN_FILENO STDOUT_FILENO STDERR_FILENO W_OK X_OK
WNOHANG WUNTRACED
WIFEXITED WEXITSTATUS WIFSIGNALED WTERMSIG WIFSTOPPED WSTOPSIG
WIFEXITED($?) returns true if the child process exited normally (exit() or by falling off the end of main())
WEXITSTATUS($?) returns the normal exit status of the child process (only meaningful if WIFEXITED($?) is true)
WIFSIGNALED($?) returns true if the child process terminated because of a signal
WTERMSIG($?) returns the signal the child process terminated for (only meaningful if WIFSIGNALED($?) is true)
WIFSTOPPED($?) returns true if the child process is currently stopped (can happen only if you specified the WUNTRACED flag to waitpid())
WSTOPSIG($?) returns the signal the child process was stopped for (only meaningful if WIFSTOPPED($?) is true)