


IPC::Open2(3p)   Perl Programmers Reference Guide  IPC::Open2(3p)


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



30/Nov/1997            perl 5.005, patch 03                     1





IPC::Open2(3p)   Perl Programmers Reference Guide  IPC::Open2(3p)


       around open3().
























































30/Nov/1997            perl 5.005, patch 03                     2


