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IPC::Open2(3perl) Perl Programmers Reference Guide IPC::Open2(3perl)
NAME
IPC::Open2 - open a process for both reading and writing using open2()
SYNOPSIS
use IPC::Open2;
my $pid = open2(my $chld_out, my $chld_in,
'some', 'cmd', 'and', 'args');
# or passing the command through the shell
my $pid = open2(my $chld_out, my $chld_in, 'some cmd and args');
# read from parent STDIN and write to already open handle
open my $outfile, '>', 'outfile.txt' or die "open failed: $!";
my $pid = open2($outfile, '<&STDIN', 'some', 'cmd', 'and', 'args');
# read from already open handle and write to parent STDOUT
open my $infile, '<', 'infile.txt' or die "open failed: $!";
my $pid = open2('>&STDOUT', $infile, 'some', 'cmd', 'and', 'args');
# reap zombie and retrieve exit status
waitpid( $pid, 0 );
my $child_exit_status = $? >> 8;
DESCRIPTION
The open2() function runs the given command and connects $chld_out for reading and
$chld_in for writing. It's what you think should work when you try
my $pid = open(my $fh, "|cmd args|");
The $chld_in filehandle will have autoflush turned on.
If $chld_out is a string (that is, a bareword filehandle rather than a glob or a
reference) and it begins with ">&", then the child will send output directly to that file
handle. If $chld_in is a string that begins with "<&", then $chld_in will be closed in
the parent, and the child will read from it directly. In both cases, there will be a
dup(2) instead of a pipe(2) made.
If either reader or writer is the empty string or undefined, this will be replaced by an
autogenerated filehandle. If so, you must pass a valid lvalue in the parameter slot so it
can be overwritten in the caller, or an exception will be raised.
open2() returns the process ID of the child process. It doesn't return on failure: it
just raises an exception matching "/^open2:/". However, "exec" failures in the child are
not detected. You'll have to trap SIGPIPE yourself.
open2() does not wait for and reap the child process after it exits. Except for short
programs where it's acceptable to let the operating system take care of this, you need to
do this yourself. This is normally as simple as calling "waitpid $pid, 0" when you're
done with the process. Failing to do this can result in an accumulation of defunct or
"zombie" processes. See "waitpid" in perlfunc for more information.
This whole affair is quite dangerous, as you may block forever. It assumes it's going to
talk to something like bc(1), both writing to it and reading from it. This is presumably
safe because you "know" that commands like bc(1) will read a line at a time and output a
line at a time. Programs like sort(1) that read their entire input stream first, however,
are quite apt to cause deadlock.
The big problem with this approach is that if you don't have control over source code
being run in the child process, you can't control what it does with pipe buffering. Thus
you can't just open a pipe to "cat -v" and continually read and write a line from it.
The IO::Pty and Expect modules from CPAN can help with this, as they provide a real tty
(well, a pseudo-tty, actually), which gets you back to line buffering in the invoked
command again.
WARNING
The order of arguments differs from that of open3().
SEE ALSO
See IPC::Open3 for an alternative that handles STDERR as well. This function is really
just a wrapper around open3().
perl v5.34.0 2023-11-23 IPC::Open2(3perl)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-12-24 23:37 @52.15.191.241 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)