IPC::Open2(3) Perl Programmers Reference Guide IPC::Open2(3)NAME
IPC::Open2, open2 - open a process for both reading and
writing
SYNOPSIS
use IPC::Open2;
$pid = open2(\*RDR, \*WTR, 'some cmd and args');
# or
$pid = open2(\*RDR, \*WTR, 'some', 'cmd', 'and', 'args');
DESCRIPTION
The open2() function spawns the given $cmd and connects
$rdr for reading and $wtr for writing. It's what you
think should work when you try
open(HANDLE, "|cmd args|");
The write filehandle will have autoflush turned on.
If $rdr 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 $wtr is a string that begins with "<&", then WTR 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.
open2() returns the process ID of the child process. It
doesn't return on failure: it just raises an exception
matching /^open2:/.
WARNING
It will not create these file handles for you. You have
to do this yourself. So don't pass it empty variables
expecting them to get filled in for you.
Additionally, this is very dangerous as you may block
forever. It assumes it's going to talk to something like
bc, both writing to it and reading from it. This is
presumably safe because you "know" that commands like bc
will read a line at a time and output a line at a time.
Programs like sort 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.
SEE ALSO
See the IPC::Open3 manpage for an alternative that handles
STDERR as well. This function is really just a wrapper
16/Sep/1999 perl 5.005, patch 03 1
IPC::Open2(3) Perl Programmers Reference Guide IPC::Open2(3)
around open3().
16/Sep/1999 perl 5.005, patch 03 2