MAN page from Old RedHat 5.X perl-5.004-4.i386.rpm

IPC::Open2

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 04
Index

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 forreading 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 globor a reference) and it begins with ``>&'', then the child will send outputdirectly to that file handle. If $wtr is a string that begins with``<&'', then WTR will be closed in the parent, and the child will readfrom it directly. In both cases, there will be a dup(2) instead of apipe(2) made.

open2() returns the process ID of the child process. It doesn't return onfailure: 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 toit 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 ata 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 controlwhat it does with pipe buffering. Thus you can't just open a pipe tocat -v and continually read and write a line from it.

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