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<html><head><title>POSIX (Programming Perl)</title><!-- STYLESHEET --><link rel="stylesheet" type="text/css" href="../style/style1.css"><!-- METADATA --><!--Dublin Core Metadata--><meta name="DC.Creator" content=""><meta name="DC.Date" content=""><meta name="DC.Format" content="text/xml" scheme="MIME"><meta name="DC.Generator" content="XSLT stylesheet, xt by James Clark"><meta name="DC.Identifier" content=""><meta name="DC.Language" content="en-US"><meta name="DC.Publisher" content="O'Reilly & Associates, Inc."><meta name="DC.Source" content="" scheme="ISBN"><meta name="DC.Subject.Keyword" content=""><meta name="DC.Title" content="POSIX"><meta name="DC.Type" content="Text.Monograph"></head><body><!-- START OF BODY --><!-- TOP BANNER --><img src="gifs/smbanner.gif" usemap="#banner-map" border="0" alt="Book Home"><map name="banner-map"><AREA SHAPE="RECT" COORDS="0,0,466,71" HREF="index.htm" ALT="Programming Perl"><AREA SHAPE="RECT" COORDS="467,0,514,18" HREF="jobjects/fsearch.htm" ALT="Search this book"></map><!-- TOP NAV BAR --><div class="navbar"><table width="515" border="0"><tr><td align="left" valign="top" width="172"><a href="ch32_35.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="ch32_01.htm">Chapter 32: Standard Modules</a></td><td align="right" valign="top" width="172"><a href="ch32_37.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr></table></div><hr width="515" align="left"><!-- SECTION BODY --><h2 class="sect1">32.36. POSIX</h2><p><blockquote><pre class="programlisting">use POSIX;# Round floats up or down to nearest integer.$n = ceil($n); # round up$n = floor($n); # round down# Produces "2000-04-01" for today.$datestr = strftime("%Y-%m-%d", localtime);# Produces "Saturday 04/01/00" for same date.$datestr = strftime("%A %D", localtime);# Try new temporary filenames until we get one# that didn't already exist; see also File::Temp# on CPAN, or in v5.6.1.do { $name = tmpnam();} until sysopen(FH, $name, O_CREAT|O_EXCL|O_RDWR, 0666);# Check for whether system has insecure chown giveaway.if (sysconf(_PC_CHOWN_RESTRICTED)) { print "Hurray -- only the superuser may call chown\n";}# Find current system's uname info.my($kernel, $hostname, $release, $version, $hardware) = uname();use POSIX ":sys_wait_h";while (($dead_pid = waitpid(-1, &WNOHANG)) > 0) { # Do something with $dead_pid if you want.}# Become new session/process-group leader (needed to create daemons# unaffected by keyboard signals or exiting login shells).setsid(0) or die "setsid failed: $!";</pre></blockquote>Perl's <tt class="literal">POSIX</tt> module permits you to access all (ornearly all) the standard POSIX 1003.1 identifiers, plus a few morefrom ANSI C that we didn't know where else to put. This moduleprovides more functions than any other. See its online documentationfor the gory details or the <em class="emphasis">POSIX Programmer'sGuide</em>, by Donald Lewine (O'Reilly, 1991).</p><p>Identifiers that are parameterless <tt class="literal">#define</tt>s in C, such as <tt class="literal">EINTR</tt>or <tt class="literal">O_NDELAY</tt>, are automatically exported into your namespace asconstant functions. Functions that aren't normally available inPerl (like <tt class="literal">floor</tt>, <tt class="literal">ceil</tt>, <tt class="literal">strftime</tt>, <tt class="literal">uname</tt>, <tt class="literal">setsid</tt>,<tt class="literal">setlocale</tt>, and <tt class="literal">sysconf</tt>) are exported by default. Functionswith the same name as a Perl built-in, like <tt class="literal">open</tt>, are not exportedunless specifically requested, but most folks are likely to preferfully qualified function names to distinguish <tt class="literal">POSIX::open</tt> from<tt class="literal">CORE::open</tt>.</p><p>A few functions are not implemented because they are C-specific.If you attempt to call these, they print a message telling youthat they aren't implemented, and suggest using the Perl equivalentshould one exist. For example, trying to access the <tt class="literal">setjmp</tt>function elicits the message "<tt class="literal">setjmp() is C-specific: use eval{} instead</tt>", and <tt class="literal">tmpfile</tt> tells you to "<tt class="literal">Use methodIO::File::new_tmpfile()</tt>". (But as of 5.6.1 you should be using <tt class="literal">File::Temp</tt> instead.)</p><p>The <tt class="literal">POSIX</tt> module lets you get as close to the operating system (orthose parts of the POSIX standard addresses, at least) as any C programmercould. This lets you do some phenomenally powerful and usefulthings, like blocking signals and controlling the terminal I/O settings.However, it also means that your code will end up looking quasi-C-like.By way of useful demonstration of how to get around input buffering,here's an example of a complete program for getting unbuffered,single-character input under any POSIX system:<blockquote><pre class="programlisting">#!/usr/bin/perl -wuse strict;$| = 1;for (1..4) { my $got; print "gimme: "; $got = getone(); print "--> $got\n";}exit;BEGIN { use POSIX qw(:termios_h); my ($term, $oterm, $echo, $noecho, $fd_stdin); $fd_stdin = fileno(STDIN); $term = POSIX::Termios->new(); $term->getattr($fd_stdin); $oterm = $term->getlflag(); $echo = ECHO | ECHOK | ICANON; $noecho = $oterm & ~$echo; sub cbreak { $term->setlflag($noecho); $term->setcc(VTIME, 1); $term->setattr($fd_stdin, TCSANOW); } sub cooked { $term->setlflag($oterm); $term->setcc(VTIME, 0); $term->setattr($fd_stdin, TCSANOW); } sub getone { my $key = ""; cbreak(); sysread(STDIN, $key, 1); cooked(); return $key; }}END { cooked() }</pre></blockquote>The <tt class="literal">POSIX</tt> module's manpage provides a completelisting of which functions and constants it exports. It has somany that you'll often wind up importing only a subset ofthem, such as "<tt class="literal">:sys_wait_h</tt>", "<tt class="literal">:sys_stat_h</tt>", or "<tt class="literal">:termios_h"</tt>.An example of blocking signals with the <tt class="literal">POSIX</tt> module is given in<a href="ch16_01.htm">Chapter 16, "Interprocess Communication"</a>.</p><!-- BOTTOM NAV BAR --><hr width="515" align="left"><div class="navbar"><table width="515" border="0"><tr><td align="left" valign="top" width="172"><a href="ch32_35.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0"></a></td><td align="right" valign="top" width="172"><a href="ch32_37.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr><tr><td align="left" valign="top" width="172">32.35. 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