1package IPC::Open2; 2 3use strict; 4 5require 5.006; 6use Exporter 'import'; 7 8our $VERSION = 1.06; 9our @EXPORT = qw(open2); 10 11=head1 NAME 12 13IPC::Open2 - open a process for both reading and writing using open2() 14 15=head1 SYNOPSIS 16 17 use IPC::Open2; 18 19 my $pid = open2(my $chld_out, my $chld_in, 20 'some', 'cmd', 'and', 'args'); 21 # or passing the command through the shell 22 my $pid = open2(my $chld_out, my $chld_in, 'some cmd and args'); 23 24 # read from parent STDIN and write to already open handle 25 open my $outfile, '>', 'outfile.txt' or die "open failed: $!"; 26 my $pid = open2($outfile, '<&STDIN', 'some', 'cmd', 'and', 'args'); 27 28 # read from already open handle and write to parent STDOUT 29 open my $infile, '<', 'infile.txt' or die "open failed: $!"; 30 my $pid = open2('>&STDOUT', $infile, 'some', 'cmd', 'and', 'args'); 31 32 # reap zombie and retrieve exit status 33 waitpid( $pid, 0 ); 34 my $child_exit_status = $? >> 8; 35 36=head1 DESCRIPTION 37 38The open2() function runs the given command and connects $chld_out for 39reading and $chld_in for writing. It's what you think should work 40when you try 41 42 my $pid = open(my $fh, "|cmd args|"); 43 44The $chld_in filehandle will have autoflush turned on. 45 46If $chld_out is a string (that is, a bareword filehandle rather than a glob 47or a reference) and it begins with C<< >& >>, then the child will send output 48directly to that file handle. If $chld_in is a string that begins with 49C<< <& >>, then $chld_in will be closed in the parent, and the child will 50read from it directly. In both cases, there will be a L<dup(2)> instead of a 51L<pipe(2)> made. 52 53If either reader or writer is the empty string or undefined, this will be 54replaced by an autogenerated filehandle. If so, you must pass a valid lvalue 55in the parameter slot so it can be overwritten in the caller, or 56an exception will be raised. 57 58open2() returns the process ID of the child process. It doesn't return on 59failure: it just raises an exception matching C</^open2:/>. However, 60C<exec> failures in the child are not detected. You'll have to 61trap SIGPIPE yourself. 62 63open2() does not wait for and reap the child process after it exits. 64Except for short programs where it's acceptable to let the operating system 65take care of this, you need to do this yourself. This is normally as 66simple as calling C<waitpid $pid, 0> when you're done with the process. 67Failing to do this can result in an accumulation of defunct or "zombie" 68processes. See L<perlfunc/waitpid> for more information. 69 70This whole affair is quite dangerous, as you may block forever. It 71assumes it's going to talk to something like L<bc(1)>, both writing 72to it and reading from it. This is presumably safe because you 73"know" that commands like L<bc(1)> will read a line at a time and 74output a line at a time. Programs like L<sort(1)> that read their 75entire input stream first, however, are quite apt to cause deadlock. 76 77The big problem with this approach is that if you don't have control 78over source code being run in the child process, you can't control 79what it does with pipe buffering. Thus you can't just open a pipe to 80C<cat -v> and continually read and write a line from it. 81 82The L<IO::Pty> and L<Expect> modules from CPAN can help with this, as 83they provide a real tty (well, a pseudo-tty, actually), which gets you 84back to line buffering in the invoked command again. 85 86=head1 WARNING 87 88The order of arguments differs from that of open3(). 89 90=head1 SEE ALSO 91 92See L<IPC::Open3> for an alternative that handles STDERR as well. This 93function is really just a wrapper around open3(). 94 95=cut 96 97# &open2: tom christiansen, <tchrist@convex.com> 98# 99# usage: $pid = open2('rdr', 'wtr', 'some cmd and args'); 100# or $pid = open2('rdr', 'wtr', 'some', 'cmd', 'and', 'args'); 101# 102# spawn the given $cmd and connect $rdr for 103# reading and $wtr for writing. return pid 104# of child, or 0 on failure. 105# 106# WARNING: this is dangerous, as you may block forever 107# unless you are very careful. 108# 109# $wtr is left unbuffered. 110# 111# abort program if 112# rdr or wtr are null 113# a system call fails 114 115require IPC::Open3; 116 117sub open2 { 118 local $Carp::CarpLevel = $Carp::CarpLevel + 1; 119 return IPC::Open3::_open3('open2', $_[1], $_[0], '>&STDERR', @_[2 .. $#_]); 120} 121 1221 123