perl5 Document that various POSIX functions need an argument, unlike their core equivalents that use `$

Migrated from rt.perl.org#132145 (status was 'open')

Searchable as RT132145$

Sep 22 '17 21:09 p5pRT

From @eserte

This is a bug report for perl from slaven@rezic.de, generated with the help of perlbug 1.40 running under perl 5.27.4.

The POSIX Pod says for localtime:

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

However, it is only identical if the optional argument is given --- POSIX::localtime fails if the argument is missing:

$ perl5.27.4 -MPOSIX -e 'warn localtime(time); warn POSIX::localtime(time)' 5982322811752641 at -e line 1. 5982322811752641 at -e line 1.

$ perl5.27.4 -MPOSIX -e 'warn localtime(); warn POSIX::localtime()'
2292322811752641 at -e line 1. Usage: POSIX::localtime(time) at -e line 1.

This seems to be the case since 5.8.x, at least (checked with 5.8.8).

I would expect that the documentation is adjusted, or that POSIX::localtime may deal with a missing argument.

Flags: category=library severity=low module=POSIX

This perlbug was built using Perl 5.20.2 - Sat Jun 3 12:27:58 UTC 2017 It is being executed now by Perl 5.27.4 - Thu Sep 21 00:25:50 CEST 2017.

Site configuration information for perl 5.27.4:

Configured by eserte at Thu Sep 21 00:25:50 CEST 2017.

Summary of my perl5 (revision 5 version 27 subversion 4) configuration:
Platform: osname=linux osvers=3.16.0-4-amd64 archname=x86_64-linux uname='linux cabulja 3.16.0-4-amd64 #1 smp debian 3.16.39-1+deb8u2 (2017-03-07) x86_64 gnulinux ' config_args='-ds -e -Dprefix=/opt/perl-5.27.4 -Dusedevel -Dusemallocwrap=no -Dcf_email=srezic@cpan.org' hint=recommended useposix=true d_sigaction=define useithreads=undef usemultiplicity=undef use64bitint=define use64bitall=define uselongdouble=undef usemymalloc=n default_inc_excludes_dot=define bincompat5005=undef Compiler: cc='cc' ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2' optimize='-O2' cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include' ccversion='' gccversion='4.9.2' gccosandvers='' intsize=4 longsize=8 ptrsize=8 doublesize=8 byteorder=12345678 doublekind=3 d_longlong=define longlongsize=8 d_longdbl=define longdblsize=16 longdblkind=3 ivtype='long' ivsize=8 nvtype='double' nvsize=8 Off_t='off_t' lseeksize=8 alignbytes=8 prototype=define Linker and Libraries: ld='cc' ldflags =' -fstack-protector-strong -L/usr/local/lib' libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc libc=libc-2.19.so so=so useshrplib=false libperl=libperl.a gnulibc_version='2.19' Dynamic Linking: dlsrc=dl_dlopen.xs dlext=so d_dlsymun=undef ccdlflags='-Wl,-E' cccdlflags='-fPIC' lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'

@INC for perl 5.27.4: /opt/perl-5.27.4/lib/site_perl/5.27.4/x86_64-linux /opt/perl-5.27.4/lib/site_perl/5.27.4 /opt/perl-5.27.4/lib/5.27.4/x86_64-linux /opt/perl-5.27.4/lib/5.27.4

Environment for perl 5.27.4: HOME=/home/eserte LANG=en_US.UTF-8 LANGUAGE (unset) LD_LIBRARY_PATH (unset) LOGDIR (unset) PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/eserte/bin/linux-gnu:/home/eserte/bin/sh:/home/eserte/bin:/home/eserte/bin/pistachio-perl/bin:/usr/games:/home/eserte/devel PERLDOC=-MPod::Perldoc::ToTextOverstrike PERL_BADLANG (unset) SHELL=/bin/zsh

Sep 22 '17 21:09 p5pRT

From @jkeenan

On Fri, 22 Sep 2017 21:13:47 GMT, slaven@rezic.de wrote:

This is a bug report for perl from slaven@rezic.de, generated with the help of perlbug 1.40 running under perl 5.27.4.

----------------------------------------------------------------- The POSIX Pod says for localtime:

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

However, it is only identical if the optional argument is given --- POSIX::localtime fails if the argument is missing:

$ perl5.27.4 -MPOSIX -e 'warn localtime(time); warn POSIX::localtime(time)' 5982322811752641 at -e line 1. 5982322811752641 at -e line 1.

$ perl5.27.4 -MPOSIX -e 'warn localtime(); warn POSIX::localtime()' 2292322811752641 at -e line 1. Usage: POSIX::localtime(time) at -e line 1.

This seems to be the case since 5.8.x, at least (checked with 5.8.8).

I would expect that the documentation is adjusted, or that POSIX::localtime may deal with a missing argument.

This is a problem more general than simply POSIX::localtime(). I suspect it affects all POSIX::*() functions which claim to be identical to the Perl builtins of the same name and which, in core, work with an implicit $_. The POSIX::* functions appear to require an explicit argument.

This makes sense to me because the POSIX specifications don't have the equivalent of our topic variable.

I grepped the CPAN POSIX documentation for those functions which are claimed to work the same in both places. See attachment 132145-posix-identical-to-perl.txt.

I then began to write a test file comparing the builtins and the POSIX variants, with and without explicit arguments. See attachment 132145-core-vs-posix.t. (This test file should be extended to all functions named in the other attachment.)

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX.

Thank you very much. -- James E Keenan (jkeenan@cpan.org)

Sep 24 '17 18:09 p5pRT

From @jkeenan

# perl use strict; use warnings; use 5.10.1; use Carp; use POSIX (); use File::Spec; use File::Temp qw( tempfile ); use Cwd; use Test::More qw( no_plan );

my $val;

{ # abs $val = -3; $_ = $val; is(abs($val), POSIX::abs($val), 'abs and POSIX::abs match when each is provided with a value'); { local $@; eval { is(abs(), POSIX::abs(), 'abs with $_'); }; chomp($@); pass("POSIX::abs requires explicit argument: $@"); } }

{ # alarm my ($start_time, $end_time, $core_msg, $posix_msg);
$val = 3; local $@; eval { local $SIG{ALRM} = sub { $end_time = time; die "ALARM!\n" }; $start_time = time; alarm $val;
# perlfunc recommends against using sleep in combination with alarm. 1 while (($end_time = time) - $start_time < 6); alarm 0; }; alarm 0; $core_msg = $@;

local $@; eval { local $SIG{ALRM} = sub { $end_time = time; die "ALARM!\n" }; $start_time = time; POSIX::alarm $val;
# perlfunc recommends against using sleep in combination with POSIX::alarm. 1 while (($end_time = time) - $start_time < 6); POSIX::alarm 0; }; POSIX::alarm 0; $posix_msg = $@;
is($posix_msg, $core_msg, "alarm and POSIX::alarm match when each is provided with a value"); ($posix_msg, $core_msg) = (undef) x 2;

$_ = $val;

local $@; eval { local $SIG{ALRM} = sub { $end_time = time; die "ALARM!\n" }; $start_time = time; alarm;
# perlfunc recommends against using sleep in combination with alarm. 1 while (($end_time = time) - $start_time < 6); alarm 0; }; alarm 0; $core_msg = $@;

{ local $@; eval { local $SIG{ALRM} = sub { $end_time = time; die "ALARM!\n" }; $start_time = time; POSIX::alarm; }; chomp($@); pass("POSIX::alarm requires explicit argument: $@"); }; }

{ # atan2 my ($y, $x); ($y, $x) = (3, 1); is(POSIX::atan2($y, $x), atan2($y, $x), "atan2 and POSIX::atan2 match; need 2 args"); }

{ # chdir skip '$ENV{HOME} not found', 2 unless $ENV{HOME};

my $homedir = $ENV{HOME}; my $tdir = File::Spec->tmpdir(); my ($adir, $bdir);

chdir($tdir) or croak "Unable to change to a different starting directory"; chdir($homedir); $adir = getcwd;

chdir($tdir) or croak "Unable to change to a different starting directory"; POSIX::chdir($homedir); $bdir = getcwd;

is($bdir, $adir, "chdir and POSIX::chdir match when each is provided with a value"); ($adir, $bdir) = (undef) x 2;

chdir($tdir) or croak "Unable to change to a different starting directory"; chdir(); $adir = getcwd;

{ local $@; chdir($tdir) or croak "Unable to change to a different starting directory"; eval { POSIX::chdir(); }; chomp($@); pass("POSIX::chdir requires explicit argument: $@"); } }

{ # chmod my ($fh1, $tfile1) = tempfile(UNLINK => 1); my ($fh2, $tfile2) = tempfile(UNLINK => 1); my ($acount, $bcount);

chmod 0644, $tfile1, $tfile2; $acount = chmod 0664, $tfile1, $tfile2;

{ chmod 0644, $tfile1, $tfile2; local $@; eval { $bcount = POSIX::chmod 0664, $tfile1, $tfile2; }; chomp($@); pass("POSIX::chmod appears to take only one argument after mode: $@"); } }

{ # localtime my (@lt, @plt); my $val;
$val = 300_000; @lt = localtime($val); @plt = POSIX::localtime($val); is_deeply(\@plt, \@lt, "localtime and POSIX::localtime match when each is provided explicit value"); undef(@lt); undef(@plt);

$_ = $val; @lt = localtime(); { local $@; eval { @plt = POSIX::localtime(); }; chomp($@); pass("POSIX::localtime requires explicit argument: $@"); } }

Sep 24 '17 18:09 p5pRT

From @jkeenan

information on most features. Consult perlfunc for functions which are noted as being identical to Perl's builtin functions.

"abs" This is identical to Perl's builtin "abs()" function, returning

"alarm" This is identical to Perl's builtin "alarm()" function, either for

"atan2" This is identical to Perl's builtin "atan2()" function, returning

"chdir" This is identical to Perl's builtin "chdir()" function, allowing

"chmod" This is identical to Perl's builtin "chmod()" function, allowing

"chown" This is identical to Perl's builtin "chown()" function, allowing "closedir" This is identical to Perl's builtin "closedir()" function for

"cos" This is identical to Perl's builtin "cos()" function, for

"exit" This is identical to Perl's builtin "exit()" function for exiting

"exp" This is identical to Perl's builtin "exp()" function for returning

"fabs" This is identical to Perl's builtin "abs()" function for returning

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

"fork" This is identical to Perl's builtin "fork()" function for

"getc" This is identical to Perl's builtin "getc()" function, see "getc" "getgrgid" This is identical to Perl's builtin "getgrgid()" function for "getgrnam" This is identical to Perl's builtin "getgrnam()" function for "getlogin" This is identical to Perl's builtin "getlogin()" function for "getpgrp" This is identical to Perl's builtin "getpgrp()" function for "getppid" This is identical to Perl's builtin "getppid()" function for "getpwnam" This is identical to Perl's builtin "getpwnam()" function for "getpwuid" This is identical to Perl's builtin "getpwuid()" function for "gmtime" This is identical to Perl's builtin "gmtime()" function for

"kill" This is identical to Perl's builtin "kill()" function for sending

"link" This is identical to Perl's builtin "link()" function for creating "localtime" This is identical to Perl's builtin "localtime()" function for

"log" This is identical to Perl's builtin "log()" function, returning

"mkdir" This is identical to Perl's builtin "mkdir()" function for "readdir" This is identical to Perl's builtin "readdir()" function for "remove" This is identical to Perl's builtin "unlink()" function for "rename" This is identical to Perl's builtin "rename()" function for "rewinddir" This is identical to Perl's builtin "rewinddir()" function for

"rmdir" This is identical to Perl's builtin "rmdir()" function for

"sin" This is identical to Perl's builtin "sin()" function for returning

"sleep" This is functionally identical to Perl's builtin "sleep()"

"sqrt" This is identical to Perl's builtin "sqrt()" function. for

"stat" This is identical to Perl's builtin "stat()" function for "strstr" This is identical to Perl's builtin "index()" function, see "system" This is identical to Perl's builtin "system()" function, see

"time" This is identical to Perl's builtin "time()" function for

"umask" This is identical to Perl's builtin "umask()" function for setting "unlink" This is identical to Perl's builtin "unlink()" function for

"utime" This is identical to Perl's builtin "utime()" function for

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

Sep 24 '17 18:09 p5pRT

The RT System itself - Status changed from 'new' to 'open'

Sep 24 '17 18:09 p5pRT

From @cpansprout

On Sun, 24 Sep 2017 11:17:07 -0700, jkeenan wrote:

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX.

I agree.

--

Father Chrysostomos

Sep 24 '17 20:09 p5pRT

From @xsawyerx

On 09/24/2017 10:21 PM, Father Chrysostomos via RT wrote:

On Sun, 24 Sep 2017 11:17:07 -0700, jkeenan wrote:

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX. I agree.

I agree as well.

Sep 25 '17 10:09 p5pRT

From @jkeenan

On Mon, 25 Sep 2017 10:37:31 GMT, xsawyerx@gmail.com wrote:

On 09/24/2017 10:21 PM, Father Chrysostomos via RT wrote:

On Sun, 24 Sep 2017 11:17:07 -0700, jkeenan wrote:

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX. I agree.

I agree as well.

So here is a plan.

1. We should work through the list of POSIX::* functions cited in attachment https://rt-archive.perl.org/perl5/Ticket/Attachment/1493177/804012/132145-posix-identical-to-perl.txt, updating the documentation to indicate how the POSIX function differs from the core function.

2. Where necessary, we should add tests which demonstrate that difference. I say "where necessary" because it turns out that the fact that some POSIX::* functions fail if provided 0 arguments is already tested in ext/POSIX/t/usage.t.

##### $> cd t; ./perl harness -v ../ext/POSIX/t/usage.t; cd - ... ok 230 - POSIX::localtime for 0 arguments gives expected error ok 231 - POSIX::localtime(1, 2) fails ok 232 - POSIX::localtime for 2 arguments gives expected error ok 233 - POSIX::localtime(1, 2, 3) fails ok 234 - POSIX::localtime for 3 arguments gives expected error #####

3. I'll start this off with the case of 'POSIX::localtime', since that was the original concern of this RT. Documentation updated in commit dc416353138cab69d334678ddd9a81b590030ef2.

4. Since there are quite a few POSIX::* functions whose documentation needs to be patched, we can do this in small batches. Anyone who hasn't had a commit to the core distribution recently (or ever) is encouraged to pick one of the remaining functions and write a documentation + test patch along the lines of mine for 'localtime' (assuming people don't have objections to that patch).

Thank you very much.

-- James E Keenan (jkeenan@cpan.org)

Sep 26 '17 13:09 p5pRT

From [email protected]

* James E Keenan via RT (perlbug-followup@perl.org) [170926 13:03]:

1. We should work through the list of POSIX::* functions cited in attachment https://rt-archive.perl.org/perl5/Ticket/Attachment/1493177/804012/132145-posix-identical-to-perl.txt, updating the documentation to indicate how the POSIX function differs from the core function.

Do you know about this manual page: https://metacpan.org/pod/release/MARKOV/POSIX-1003-0.99_07/lib/POSIX/Overview.pod There are some warnings in there.

It started off with my rewrite of the POSIX.pm manual page, which never went into core. Find attached. It may be of help to you. -- Regards, MarkOv

Mark Overmeer MSc MARKOV Solutions Mark@Overmeer.net solutions@overmeer.net http://Mark.Overmeer.net http://solutions.overmeer.net

Sep 26 '17 19:09 p5pRT

From [email protected]

=head1 NAME

POSIX - Perl interface to IEEE Std 1003.1

=head1 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

=head1 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.

I<Everything is exported by default> with the exception of any POSIX functions with the same name as a built-in Perl function, such as C<abs>, C<alarm>, C<rmdir>, C<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 C<use POSIX ()> and then use the fully qualified names (ie. C<POSIX::SEEK_END>), or by giving an explicit import list. If you do neither, and opt for the default, C<use POSIX;> has to import I<553 symbols>.

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 L<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.

=head1 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.

=head1 FUNCTIONS

=over 8

=item _exit

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

Note that when using threads and in Linux this is B<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.

=item abort

This is identical to the C function C<abort()>. It terminates the process with a C<SIGABRT> signal unless caught by a signal handler or if the handler does not return normally (it e.g. does a C<longjmp>).

=item abs

This is identical to Perl's builtin C<abs()> function, returning the absolute value of its numerical argument.

=item access

Determines the accessibility of a file.

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

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

=item acos

This is identical to the C function C<acos()>, returning the arcus cosine of its numerical argument. See also L<Math::Trig>.

=item alarm

This is identical to Perl's builtin C<alarm()> function, either for arming or disarming the C<SIGARLM> timer.

=item asctime

This is identical to the C function C<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 C<$mon> is zero-based: January equals C<0>. The C<$year> is 1900-based: 2001 equals C<101>. C<$wday> and C<$yday> default to zero (and are usually ignored anyway), and C<$isdst> defaults to -1.

=item asin

This is identical to the C function C<asin()>, returning the arcus sine of its numerical argument. See also L<Math::Trig>.

=item assert

Unimplemented, but you can use L<perlfunc/die> and the L<Carp> module to achieve similar things.

=item atan

This is identical to the C function C<atan()>, returning the arcus tangent of its numerical argument. See also L<Math::Trig>.

=item atan2

This is identical to Perl's builtin C<atan2()> function, returning the arcus tangent defined by its two numerical arguments, the I<y> coordinate and the I<x> coordinate. See also L<Math::Trig>.

=item atexit

atexit() is C-specific: use C<END {}> instead, see L<perlsub>.

=item 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.

=item 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 L<perlfunc/int>.

=item 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 L<perlfunc/int>.

=item bsearch

bsearch() not supplied. For doing binary search on wordlists, see L<Search::Dict>.

=item calloc

calloc() is C-specific. Perl does memory management transparently.

=item ceil

This is identical to the C function C<ceil()>, returning the smallest integer value greater than or equal to the given numerical argument.

=item chdir

This is identical to Perl's builtin C<chdir()> function, allowing one to change the working (default) directory, see L<perlfunc/chdir>.

=item chmod

This is identical to Perl's builtin C<chmod()> function, allowing one to change file and directory permissions, see L<perlfunc/chmod>.

=item chown

This is identical to Perl's builtin C<chown()> function, allowing one to change file and directory owners and groups, see L<perlfunc/chown>.

=item clearerr

Use the method C<IO::Handle::clearerr()> instead, to reset the error state (if any) and EOF state (if any) of the given stream.

=item clock

This is identical to the C function C<clock()>, returning the amount of spent processor time in microseconds.

=item close

Close the file. This uses file descriptors such as those obtained by calling C<POSIX::open>.

$fd = POSIX::open( "foo", &POSIX::O_RDONLY ); POSIX::close( $fd );

Returns C<undef> on failure.

See also L<perlfunc/close>.

=item closedir

This is identical to Perl's builtin C<closedir()> function for closing a directory handle, see L<perlfunc/closedir>.

=item cos

This is identical to Perl's builtin C<cos()> function, for returning the cosine of its numerical argument, see L<perlfunc/cos>. See also L<Math::Trig>.

=item cosh

This is identical to the C function C<cosh()>, for returning the hyperbolic cosine of its numeric argument. See also L<Math::Trig>.

=item creat

Create a new file. This returns a file descriptor like the ones returned by C<POSIX::open>. Use C<POSIX::close> to close the file.

$fd = POSIX::creat( "foo", 0611 ); POSIX::close( $fd );

See also L<perlfunc/sysopen> and its C<O_CREAT> flag.

=item ctermid

Generates the path name for the controlling terminal.

$path = POSIX::ctermid();

=item ctime

This is identical to the C function C<ctime()> and equivalent to C<asctime(localtime(...))>, see L</asctime> and L</localtime>.

=item cuserid

Get the login name of the owner of the current process.

$name = POSIX::cuserid();

=item difftime

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

=item div

div() is C-specific, use L<perlfunc/int> on the usual C</> division and the modulus C<%>.

=item dup

This is similar to the C function C<dup()>, for duplicating a file descriptor.

This uses file descriptors such as those obtained by calling C<POSIX::open>.

Returns C<undef> on failure.

=item dup2

This is similar to the C function C<dup2()>, for duplicating a file descriptor to an another known file descriptor.

This uses file descriptors such as those obtained by calling C<POSIX::open>.

Returns C<undef> on failure.

=item errno

Returns the value of errno.

$errno = POSIX::errno();

This identical to the numerical values of the C<$!>, see L<perlvar/$ERRNO>.

=item execl

execl() is C-specific, see L<perlfunc/exec>.

=item execle

execle() is C-specific, see L<perlfunc/exec>.

=item execlp

execlp() is C-specific, see L<perlfunc/exec>.

=item execv

execv() is C-specific, see L<perlfunc/exec>.

=item execve

execve() is C-specific, see L<perlfunc/exec>.

=item execvp

execvp() is C-specific, see L<perlfunc/exec>.

=item exit

This is identical to Perl's builtin C<exit()> function for exiting the program, see L<perlfunc/exit>.

=item exp

This is identical to Perl's builtin C<exp()> function for returning the exponent (I<e>-based) of the numerical argument, see L<perlfunc/exp>.

=item fabs

This is identical to Perl's builtin C<abs()> function for returning the absolute value of the numerical argument, see L<perlfunc/abs>.

=item fclose

Use method C<IO::Handle::close()> instead, or see L<perlfunc/close>.

=item fcntl

This is identical to Perl's builtin C<fcntl()> function, see L<perlfunc/fcntl>.

=item fdopen

Use method C<IO::Handle::new_from_fd()> instead, or see L<perlfunc/open>.

=item feof

Use method C<IO::Handle::eof()> instead, or see L<perlfunc/eof>.

=item ferror

Use method C<IO::Handle::error()> instead.

=item fflush

Use method C<IO::Handle::flush()> instead. See also L<perlvar/$OUTPUT_AUTOFLUSH>.

=item fgetc

Use method C<IO::Handle::getc()> instead, or see L<perlfunc/read>.

=item fgetpos

Use method C<IO::Seekable::getpos()> instead, or see L<perlfunc/seek>.

=item fgets

Use method C<IO::Handle::gets()> instead. Similar to E<lt>E<gt>, also known as L<perlfunc/readline>.

=item fileno

Use method C<IO::Handle::fileno()> instead, or see L<perlfunc/fileno>.

=item floor

This is identical to the C function C<floor()>, returning the largest integer value less than or equal to the numerical argument.

=item fmod

This is identical to the C function C<fmod()>.

$r = fmod($x, $y);

It returns the remainder C<$r = $x - $n*$y>, where C<$n = trunc($x/$y)>. The C<$r> has the same sign as C<$x> and magnitude (absolute value) less than the magnitude of C<$y>.

=item fopen

Use method C<IO::File::open()> instead, or see L<perlfunc/open>.

=item fork

This is identical to Perl's builtin C<fork()> function for duplicating the current process, see L<perlfunc/fork> and L<perlfork> if you are in Windows.

=item fpathconf

Retrieves the value of a configurable limit on a file or directory. This uses file descriptors such as those obtained by calling C<POSIX::open>.

The following will determine the maximum length of the longest allowable pathname on the filesystem which holds C</var/foo>.

$fd = POSIX::open( "/var/foo", &POSIX::O_RDONLY ); $path_max = POSIX::fpathconf( $fd, &POSIX::_PC_PATH_MAX );

Returns C<undef> on failure.

=item fprintf

fprintf() is C-specific, see L<perlfunc/printf> instead.

=item fputc

fputc() is C-specific, see L<perlfunc/print> instead.

=item fputs

fputs() is C-specific, see L<perlfunc/print> instead.

=item fread

fread() is C-specific, see L<perlfunc/read> instead.

=item free

free() is C-specific. Perl does memory management transparently.

=item freopen

freopen() is C-specific, see L<perlfunc/open> instead.

=item frexp

Return the mantissa and exponent of a floating-point number.

($mantissa, $exponent) = POSIX::frexp( 1.234e56 );

=item fscanf

fscanf() is C-specific, use E<lt>E<gt> and regular expressions instead.

=item fseek

Use method C<IO::Seekable::seek()> instead, or see L<perlfunc/seek>.

=item fsetpos

Use method C<IO::Seekable::setpos()> instead, or seek L<perlfunc/seek>.

=item fstat

Get file status. This uses file descriptors such as those obtained by calling C<POSIX::open>. The data returned is identical to the data from Perl's builtin C<stat> function.

$fd = POSIX::open( "foo", &POSIX::O_RDONLY ); @stats = POSIX::fstat( $fd );

=item fsync

Use method C<IO::Handle::sync()> instead.

=item ftell

Use method C<IO::Seekable::tell()> instead, or see L<perlfunc/tell>.

=item fwrite

fwrite() is C-specific, see L<perlfunc/print> instead.

=item getc

This is identical to Perl's builtin C<getc()> function, see L<perlfunc/getc>.

=item getchar

Returns one character from STDIN. Identical to Perl's C<getc()>, see L<perlfunc/getc>.

=item getcwd

Returns the name of the current working directory. See also L<Cwd>.

=item getegid

Returns the effective group identifier. Similar to Perl' s builtin variable C<$(>, see L<perlvar/$EGID>.

=item getenv

Returns the value of the specified environment variable. The same information is available through the C<%ENV> array.

=item geteuid

Returns the effective user identifier. Identical to Perl's builtin C<$E<gt>> variable, see L<perlvar/$EUID>.

=item getgid

Returns the user's real group identifier. Similar to Perl's builtin variable C<$)>, see L<perlvar/$GID>.

=item getgrgid

This is identical to Perl's builtin C<getgrgid()> function for returning group entries by group identifiers, see L<perlfunc/getgrgid>.

=item getgrnam

This is identical to Perl's builtin C<getgrnam()> function for returning group entries by group names, see L<perlfunc/getgrnam>.

=item getgroups

Returns the ids of the user's supplementary groups. Similar to Perl's builtin variable C<$)>, see L<perlvar/$GID>.

=item getlogin

This is identical to Perl's builtin C<getlogin()> function for returning the user name associated with the current session, see L<perlfunc/getlogin>.

=item getpgrp

This is identical to Perl's builtin C<getpgrp()> function for returning the process group identifier of the current process, see L<perlfunc/getpgrp>.

=item getpid

Returns the process identifier. Identical to Perl's builtin variable C<$$>, see L<perlvar/$PID>.

=item getppid

This is identical to Perl's builtin C<getppid()> function for returning the process identifier of the parent process of the current process , see L<perlfunc/getppid>.

=item getpwnam

This is identical to Perl's builtin C<getpwnam()> function for returning user entries by user names, see L<perlfunc/getpwnam>.

=item getpwuid

This is identical to Perl's builtin C<getpwuid()> function for returning user entries by user identifiers, see L<perlfunc/getpwuid>.

=item gets

Returns one line from C<STDIN>, similar to E<lt>E<gt>, also known as the C<readline()> function, see L<perlfunc/readline>.

B<NOTE>: if you have C programs that still use C<gets()>, be very afraid. The C<gets()> function is a source of endless grief because it has no buffer overrun checks. It should B<never> be used. The C<fgets()> function should be preferred instead.

=item getuid

Returns the user's identifier. Identical to Perl's builtin C<$E<lt>> variable, see L<perlvar/$UID>.

=item gmtime

This is identical to Perl's builtin C<gmtime()> function for converting seconds since the epoch to a date in Greenwich Mean Time, see L<perlfunc/gmtime>.

=item 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 C<isalnum>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:alnum:]]/> construct instead, or possibly the C</\w/> construct.

=item 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 C<isalpha>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:alpha:]]/> construct instead.

=item isatty

Returns a boolean indicating whether the specified filehandle is connected to a tty. Similar to the C<-t> operator, see L<perlfunc/-X>.

=item 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 C<iscntrl>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:cntrl:]]/> construct instead.

=item 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 C<isdigit> (unlikely, but still possible). Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:digit:]]/> construct instead, or the C</\d/> construct.

=item 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 C<isgraph>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:graph:]]/> construct instead.

=item 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 C<islower>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:lower:]]/> construct instead. Do B<not> use C</[a-z]/>.

=item 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 C<isprint>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:print:]]/> construct instead.

=item 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 C<ispunct>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:punct:]]/> construct instead.

=item 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 C<isspace>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:space:]]/> construct instead, or the C</\s/> construct. (Note that C</\s/> and C</[[:space:]]/> are slightly different in that C</[[:space:]]/> can normally match a vertical tab, while C</\s/> does not.)

=item 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 C<isupper>. Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:upper:]]/> construct instead. Do B<not> use C</[A-Z]/>.

=item 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 C<isxdigit> (unlikely, but still possible). Does not work on Unicode characters code point 256 or higher. Consider using regular expressions and the C</[[:xdigit:]]/> construct instead, or simply C</[0-9a-f]/i>.

=item kill

This is identical to Perl's builtin C<kill()> function for sending signals to processes (often to terminate them), see L<perlfunc/kill>.

=item labs

(For returning absolute values of long integers.) labs() is C-specific, see L<perlfunc/abs> instead.

=item lchown

This is identical to the C function, except the order of arguments is consistent with Perl's builtin C<chown()> with the added restriction of only one path, not an list of paths. Does the same thing as the C<chown()> function but changes the owner of a symbolic link instead of the file the symbolic link points to.

=item ldexp

This is identical to the C function C<ldexp()> for multiplying floating point numbers with powers of two.

$x_quadrupled = POSIX::ldexp($x, 2);

=item ldiv

(For computing dividends of long integers.) ldiv() is C-specific, use C</> and C<int()> instead.

=item link

This is identical to Perl's builtin C<link()> function for creating hard links into files, see L<perlfunc/link>.

=item 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 B<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";

=item localtime

This is identical to Perl's builtin C<localtime()> function for converting seconds since the epoch to a date see L<perlfunc/localtime>.

=item log

This is identical to Perl's builtin C<log()> function, returning the natural (I<e>-based) logarithm of the numerical argument, see L<perlfunc/log>.

=item log10

This is identical to the C function C<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 }

=item longjmp

longjmp() is C-specific: use L<perlfunc/die> instead.

=item lseek

Move the file's read/write position. This uses file descriptors such as those obtained by calling C<POSIX::open>.

$fd = POSIX::open( "foo", &POSIX::O_RDONLY ); $off_t = POSIX::lseek( $fd, 0, &POSIX::SEEK_SET );

Returns C<undef> on failure.

=item malloc

malloc() is C-specific. Perl does memory management transparently.

=item mblen

This is identical to the C function C<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.

=item mbstowcs

This is identical to the C function C<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.

=item mbtowc

This is identical to the C function C<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.

=item memchr

memchr() is C-specific, see L<perlfunc/index> instead.

=item memcmp

memcmp() is C-specific, use C<eq> instead, see L<perlop>.

=item memcpy

memcpy() is C-specific, use C<=>, see L<perlop>, or see L<perlfunc/substr>.

=item memmove

memmove() is C-specific, use C<=>, see L<perlop>, or see L<perlfunc/substr>.

=item memset

memset() is C-specific, use C<x> instead, see L<perlop>.

=item mkdir

This is identical to Perl's builtin C<mkdir()> function for creating directories, see L<perlfunc/mkdir>.

=item mkfifo

This is similar to the C function C<mkfifo()> for creating FIFO special files.

if (mkfifo($path, $mode)) { ....

Returns C<undef> on failure. The C<$mode> is similar to the mode of C<mkdir()>, see L<perlfunc/mkdir>, though for C<mkfifo> you B<must> specify the C<$mode>.

=item mktime

Convert date/time info to a calendar time.

Synopsis:

mktime(sec, min, hour, mday, mon, year, wday = 0, yday = 0, isdst = -1)

The month (C<mon>), weekday (C<wday>), and yearday (C<yday>) begin at zero. I.e. January is 0, not 1; Sunday is 0, not 1; January 1st is 0, not 1. The year (C<year>) is given in years since 1900. I.e. The year 1995 is 95; the year 2001 is 101. Consult your system's C<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 C<undef> on failure.

=item modf

Return the integral and fractional parts of a floating-point number.

($fractional, $integral) = POSIX::modf( 3.14 );

=item nice

This is similar to the C function C<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 C<undef> on failure.

=item offsetof

offsetof() is C-specific, you probably want to see L<perlfunc/pack> instead.

=item open

Open a file for reading for writing. This returns file descriptors, not Perl filehandles. Use C<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 C<undef> on failure.

See also L<perlfunc/sysread>.

=item readdir

This is identical to Perl's builtin C<readdir()> function for reading directory entries, see L<perlfunc/readdir>.

=item realloc

realloc() is C-specific. Perl does memory management transparently.

=item remove

This is identical to Perl's builtin C<unlink()> function for removing files, see L<perlfunc/unlink>.

=item rename

This is identical to Perl's builtin C<rename()> function for renaming files, see L<perlfunc/rename>.

=item rewind

Seeks to the beginning of the file.

=item rewinddir

This is identical to Perl's builtin C<rewinddir()> function for rewinding directory entry streams, see L<perlfunc/rewinddir>.

=item rmdir

This is identical to Perl's builtin C<rmdir()> function for removing (empty) directories, see L<perlfunc/rmdir>.

=item scanf

scanf() is C-specific, use E<lt>E<gt> and regular expressions instead, see L<perlre>.

=item setgid

Sets the real group identifier and the effective group identifier for this process. Similar to assigning a value to the Perl's builtin C<$)> variable, see L<perlvar/$EGID>, 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.

=item setjmp

C<setjmp()> is C-specific: use C<eval {}> instead, see L<perlfunc/eval>.

=item 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<"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 C<"">). Please see your systems C<setlocale(3)> documentation for the locale environment variables' meaning or consult L<perllocale>.

$loc = setlocale( LC_CTYPE, "" );

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

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

=item setpgid

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

Returns C<undef> on failure.

=item setsid

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

=item setuid

Sets the real user identifier and the effective user identifier for this process. Similar to assigning a value to the Perl's builtin C<$E<lt>> variable, see L<perlvar/$UID>, except that the latter will change only the real user identifier.

=item sigaction

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

Synopsis:

sigaction(signal, action, oldaction = 0)

Returns C<undef> on failure. The C<signal> must be a number (like SIGHUP), not a string (like "SIGHUP"), though Perl does try hard to understand you.

If you use the SA_SIGINFO flag, the signal handler will in addition to the first argument, the signal name, also receive a second argument, a hash reference, inside which are the following keys with the following semantics, as defined by POSIX/SUSv3:

signo the signal number errno the error number code if this is zero or less, the signal was sent by a user process and the uid and pid make sense, otherwise the signal was sent by the kernel

The following are also defined by POSIX/SUSv3, but unfortunately not very widely implemented:

pid the process id generating the signal uid the uid of the process id generating the signal status exit value or signal for SIGCHLD band band event for SIGPOLL

A third argument is also passed to the handler, which contains a copy of the raw binary contents of the siginfo structure: if a system has some non-POSIX fields, this third argument is where to unpack() them from.

Note that not all siginfo values make sense simultaneously (some are valid only for certain signals, for example), and not all values make sense from Perl perspective, you should to consult your system's C<sigaction> and possibly also C<siginfo> documentation.

=item siglongjmp

siglongjmp() is C-specific: use L<perlfunc/die> instead.

=item sigpending

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

Synopsis:

sigpending(sigset)

Returns C<undef> on failure.

=item sigprocmask

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

Synopsis:

sigprocmask(how, sigset, oldsigset = 0)

Returns C<undef> on failure.

Note that you can't reliably block or unblock a signal from its own signal handler if you're using safe signals. Other signals can be blocked or unblocked reliably.

=item sigsetjmp

C<sigsetjmp()> is C-specific: use C<eval {}> instead, see L<perlfunc/eval>.

=item sigsuspend

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

Synopsis:

sigsuspend(signal_mask)

Returns C<undef> on failure.

=item sin

This is identical to Perl's builtin C<sin()> function for returning the sine of the numerical argument, see L<perlfunc/sin>. See also L<Math::Trig>.

=item sinh

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

=item sleep

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

=item sprintf

This is similar to Perl's builtin C<sprintf()> function for returning a string that has the arguments formatted as requested, see L<perlfunc/sprintf>.

=item sqrt

This is identical to Perl's builtin C<sqrt()> function. for returning the square root of the numerical argument, see L<perlfunc/sqrt>.

=item srand

Give a seed the pseudorandom number generator, see L<perlfunc/srand>.

=item sscanf

sscanf() is C-specific, use regular expressions instead, see L<perlre>.

=item stat

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

=item strcat

strcat() is C-specific, use C<.=> instead, see L<perlop>.

=item strchr

strchr() is C-specific, see L<perlfunc/index> instead.

=item strcmp

strcmp() is C-specific, use C<eq> or C<cmp> instead, see L<perlop>.

=item strcoll

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

=item strcpy

strcpy() is C-specific, use C<=> instead, see L<perlop>.

=item strcspn

strcspn() is C-specific, use regular expressions instead, see L<perlre>.

=item strerror

Returns the error string for the specified errno. Identical to the string form of the C<$!>, see L<perlvar/$ERRNO>.

=item 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 (C<mon>), weekday (C<wday>), and yearday (C<yday>) begin at zero. I.e. January is 0, not 1; Sunday is 0, not 1; January 1st is 0, not 1. The year (C<year>) is given in years since 1900. I.e., the year 1995 is 95; the year 2001 is 101. Consult your system's C<strftime()> manpage for details about these and the other arguments.

If you want your code to be portable, your format (C<fmt>) argument should use only the conversion specifiers defined by the ANSI C standard (C89, to play safe). These are C<aAbBcdHIjmMpSUwWxXyYZ%>. But even then, the B<results> of some of the conversion specifiers are non-portable. For example, the specifiers C<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<c> changes according to the timezone settings of the user and the timezone computation rules of the operating system. The C<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 C<mktime()> before calling your system's C<strftime()> function, except that the C<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";

=item strlen

strlen() is C-specific, use C<length()> instead, see L<perlfunc/length>.

=item strncat

strncat() is C-specific, use C<.=> instead, see L<perlop>.

=item strncmp

strncmp() is C-specific, use C<eq> instead, see L<perlop>.

=item strncpy

strncpy() is C-specific, use C<=> instead, see L<perlop>.

=item strpbrk

strpbrk() is C-specific, use regular expressions instead, see L<perlre>.

=item strrchr

strrchr() is C-specific, see L<perlfunc/rindex> instead.

=item strspn

strspn() is C-specific, use regular expressions instead, see L<perlre>.

=item strstr

This is identical to Perl's builtin C<index()> function, see L<perlfunc/index>.

=item 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 I<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.

=item strtok

strtok() is C-specific, use regular expressions instead, see L<perlre>, or L<perlfunc/split>.

=item 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 I<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.

=item strtoul

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

=item strxfrm

String transformation. Returns the transformed string.

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

Used in conjunction with the C<strcoll()> function, see L</strcoll>.

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

=item 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 C<undef> on failure.

=item system

This is identical to Perl's builtin C<system()> function, see L<perlfunc/system>.

=item tan

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

=item tanh

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

=item tcdrain

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

Returns C<undef> on failure.

=item tcflow

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

Returns C<undef> on failure.

=item tcflush

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

Returns C<undef> on failure.

=item tcgetpgrp

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

=item tcsendbreak

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

Returns C<undef> on failure.

=item tcsetpgrp

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

Returns C<undef> on failure.

=item time

This is identical to Perl's builtin C<time()> function for returning the number of seconds since the epoch (whatever it is for the system), see L<perlfunc/time>.

=item 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 C<times()> function returns four values, measured in seconds.

=item tmpfile

Use method C<IO::File::new_tmpfile()> instead, or see L<File::Temp>.

=item 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 L<File::Temp>.

=item 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 C<lc()> function, see L<perlfunc/lc>, or the equivalent C<\L> operator inside doublequotish strings.

=item 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 C<uc()> function, see L<perlfunc/uc>, or the equivalent C<\U> operator inside doublequotish strings.

=item ttyname

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

=item tzname

Retrieves the time conversion information from the C<tzname> variable.

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

=item tzset

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

=item umask

This is identical to Perl's builtin C<umask()> function for setting (and querying) the file creation permission mask, see L<perlfunc/umask>.

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

=item ungetc

Use method C<IO::Handle::ungetc()> instead.

=item unlink

This is identical to Perl's builtin C<unlink()> function for removing files, see L<perlfunc/unlink>.

=item utime

This is identical to Perl's builtin C<utime()> function for changing the time stamps of files and directories, see L<perlfunc/utime>.

=item vfprintf

vfprintf() is C-specific, see L<perlfunc/printf> instead.

=item vprintf

vprintf() is C-specific, see L<perlfunc/printf> instead.

=item vsprintf

vsprintf() is C-specific, see L<perlfunc/sprintf> instead.

=item wait

This is identical to Perl's builtin C<wait()> function, see L<perlfunc/wait>.

=item waitpid

Wait for a child process to change state. This is identical to Perl's builtin C<waitpid()> function, see L<perlfunc/waitpid>.

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

=item wcstombs

This is identical to the C function C<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.

=item wctomb

This is identical to the C function C<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.

=item write

Write to a file. This uses file descriptors such as those obtained by calling C<POSIX::open>.

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

Returns C<undef> on failure.

From @xsawyerx

On 09/26/2017 03:03 PM, James E Keenan via RT wrote:

On Mon, 25 Sep 2017 10:37:31 GMT, xsawyerx@gmail.com wrote:

On 09/24/2017 10:21 PM, Father Chrysostomos via RT wrote:

On Sun, 24 Sep 2017 11:17:07 -0700, jkeenan wrote:

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX. I agree.

I agree as well. So here is a plan.

1. We should work through the list of POSIX::* functions cited in attachment https://rt-archive.perl.org/perl5/Ticket/Attachment/1493177/804012/132145-posix-identical-to-perl.txt, updating the documentation to indicate how the POSIX function differs from the core function.

2. Where necessary, we should add tests which demonstrate that difference. I say "where necessary" because it turns out that the fact that some POSIX::* functions fail if provided 0 arguments is already tested in ext/POSIX/t/usage.t.

##### $> cd t; ./perl harness -v ../ext/POSIX/t/usage.t; cd - ... ok 230 - POSIX::localtime for 0 arguments gives expected error ok 231 - POSIX::localtime(1, 2) fails ok 232 - POSIX::localtime for 2 arguments gives expected error ok 233 - POSIX::localtime(1, 2, 3) fails ok 234 - POSIX::localtime for 3 arguments gives expected error #####

3. I'll start this off with the case of 'POSIX::localtime', since that was the original concern of this RT. Documentation updated in commit dc416353138cab69d334678ddd9a81b590030ef2.

4. Since there are quite a few POSIX::* functions whose documentation needs to be patched, we can do this in small batches. Anyone who hasn't had a commit to the core distribution recently (or ever) is encouraged to pick one of the remaining functions and write a documentation + test patch along the lines of mine for 'localtime' (assuming people don't have objections to that patch).

That sounds like a good plan to me.

With regards to step 2, it might be easier to add the test again automatically than curate every test to see if it covers that. Create a test for all of them in a new file.

The testing part can at least be automated but perhaps some of the rest too. Adding a single line that indicates whether this uses zero or more parameters and how it compares to core (akin to the one you generarted) might be sufficient.

I wish we could track this better. Perhaps with a GH issue?

Thanks, Jim!

Sep 27 '17 12:09 p5pRT

From @jkeenan

On Wed, 27 Sep 2017 12:51:55 GMT, xsawyerx@gmail.com wrote:

On 09/26/2017 03:03 PM, James E Keenan via RT wrote:

On Mon, 25 Sep 2017 10:37:31 GMT, xsawyerx@gmail.com wrote:

On 09/24/2017 10:21 PM, Father Chrysostomos via RT wrote:

On Sun, 24 Sep 2017 11:17:07 -0700, jkeenan wrote:

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX. I agree.

I agree as well. So here is a plan.

1. We should work through the list of POSIX::* functions cited in attachment https://rt-archive.perl.org/perl5/Ticket/Attachment/1493177/804012/132145-posix- identical-to-perl.txt, updating the documentation to indicate how the POSIX function differs from the core function.

2. Where necessary, we should add tests which demonstrate that difference. I say "where necessary" because it turns out that the fact that some POSIX::* functions fail if provided 0 arguments is already tested in ext/POSIX/t/usage.t.

##### $> cd t; ./perl harness -v ../ext/POSIX/t/usage.t; cd - ... ok 230 - POSIX::localtime for 0 arguments gives expected error ok 231 - POSIX::localtime(1, 2) fails ok 232 - POSIX::localtime for 2 arguments gives expected error ok 233 - POSIX::localtime(1, 2, 3) fails ok 234 - POSIX::localtime for 3 arguments gives expected error #####

3. I'll start this off with the case of 'POSIX::localtime', since that was the original concern of this RT. Documentation updated in commit dc416353138cab69d334678ddd9a81b590030ef2.

4. Since there are quite a few POSIX::* functions whose documentation needs to be patched, we can do this in small batches. Anyone who hasn't had a commit to the core distribution recently (or ever) is encouraged to pick one of the remaining functions and write a documentation + test patch along the lines of mine for 'localtime' (assuming people don't have objections to that patch).

That sounds like a good plan to me.

With regards to step 2, it might be easier to add the test again automatically than curate every test to see if it covers that. Create a test for all of them in a new file.

The way I read the existing tests, it seems that this automation has already been accomplished by Nicholas Clark back in 2011 in ext/POSIX/t/usage.t.

What do you think is needed above and beyond that?

The testing part can at least be automated but perhaps some of the rest too. Adding a single line that indicates whether this uses zero or more parameters and how it compares to core (akin to the one you generarted) might be sufficient.

I wish we could track this better. Perhaps with a GH issue?

Thanks, Jim!

-- James E Keenan (jkeenan@cpan.org)

Sep 27 '17 14:09 p5pRT

From @xsawyerx

On 09/27/2017 04:07 PM, James E Keenan via RT wrote:

On Wed, 27 Sep 2017 12:51:55 GMT, xsawyerx@gmail.com wrote:

On 09/26/2017 03:03 PM, James E Keenan via RT wrote:

On Mon, 25 Sep 2017 10:37:31 GMT, xsawyerx@gmail.com wrote:

On 09/24/2017 10:21 PM, Father Chrysostomos via RT wrote:

On Sun, 24 Sep 2017 11:17:07 -0700, jkeenan wrote:

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX. I agree.

I agree as well. So here is a plan.

1. We should work through the list of POSIX::* functions cited in attachment https://rt-archive.perl.org/perl5/Ticket/Attachment/1493177/804012/132145-posix- identical-to-perl.txt, updating the documentation to indicate how the POSIX function differs from the core function.

2. Where necessary, we should add tests which demonstrate that difference. I say "where necessary" because it turns out that the fact that some POSIX::* functions fail if provided 0 arguments is already tested in ext/POSIX/t/usage.t.

##### $> cd t; ./perl harness -v ../ext/POSIX/t/usage.t; cd - ... ok 230 - POSIX::localtime for 0 arguments gives expected error ok 231 - POSIX::localtime(1, 2) fails ok 232 - POSIX::localtime for 2 arguments gives expected error ok 233 - POSIX::localtime(1, 2, 3) fails ok 234 - POSIX::localtime for 3 arguments gives expected error #####

3. I'll start this off with the case of 'POSIX::localtime', since that was the original concern of this RT. Documentation updated in commit dc416353138cab69d334678ddd9a81b590030ef2.

4. Since there are quite a few POSIX::* functions whose documentation needs to be patched, we can do this in small batches. Anyone who hasn't had a commit to the core distribution recently (or ever) is encouraged to pick one of the remaining functions and write a documentation + test patch along the lines of mine for 'localtime' (assuming people don't have objections to that patch).

That sounds like a good plan to me.

With regards to step 2, it might be easier to add the test again automatically than curate every test to see if it covers that. Create a test for all of them in a new file.

The way I read the existing tests, it seems that this automation has already been accomplished by Nicholas Clark back in 2011 in ext/POSIX/t/usage.t.

What do you think is needed above and beyond that?

Nothing, I guess. I thought you wanted to add more tests and documentation and I was commenting that it might not need to be a manual process.

Sep 27 '17 17:09 p5pRT

From @jkeenan

On Sun, 24 Sep 2017 18:17:07 GMT, jkeenan wrote:

On Fri, 22 Sep 2017 21:13:47 GMT, slaven@rezic.de wrote:

This is a bug report for perl from slaven@rezic.de, generated with the help of perlbug 1.40 running under perl 5.27.4.

----------------------------------------------------------------- The POSIX Pod says for localtime:

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

However, it is only identical if the optional argument is given --- POSIX::localtime fails if the argument is missing:

$ perl5.27.4 -MPOSIX -e 'warn localtime(time); warn POSIX::localtime(time)' 5982322811752641 at -e line 1. 5982322811752641 at -e line 1.

$ perl5.27.4 -MPOSIX -e 'warn localtime(); warn POSIX::localtime()' 2292322811752641 at -e line 1. Usage: POSIX::localtime(time) at -e line 1.

This seems to be the case since 5.8.x, at least (checked with 5.8.8).

I would expect that the documentation is adjusted, or that POSIX::localtime may deal with a missing argument.

This is a problem more general than simply POSIX::localtime(). I suspect it affects all POSIX::*() functions which claim to be identical to the Perl builtins of the same name and which, in core, work with an implicit $_. The POSIX::* functions appear to require an explicit argument.

This makes sense to me because the POSIX specifications don't have the equivalent of our topic variable.

I grepped the CPAN POSIX documentation for those functions which are claimed to work the same in both places. See attachment 132145-posix- identical-to-perl.txt.

I then began to write a test file comparing the builtins and the POSIX variants, with and without explicit arguments. See attachment 132145- core-vs-posix.t. (This test file should be extended to all functions named in the other attachment.)

I think that we should simply change the documentation as needed to indicate this one difference in behaviour between builtins and POSIX.

Thank you very much.

Partially done in commit bda53d3ed47d5776c4a1b88c0b7cfb484f5644be.

-- James E Keenan (jkeenan@cpan.org)

Oct 15 '17 14:10 p5pRT

This issue can be closed, per cf9d355875f10c8cf849bbb2d24b6b7877ff0e8f.

May 23 '24 14:05 book

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Document that various POSIX functions need an argument, unlike their core equivalents that use `$_`

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Document that various POSIX functions need an argument, unlike their core equivalents that use `$_`

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