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

       IPC::Open2, open2 - open a process for both reading and writing

           use IPC::Open2;
           $pid = open2(\*RDR, \*WTR, 'some cmd and args');
             # or
           $pid = open2(\*RDR, \*WTR, 'some', 'cmd', 'and', 'args');

       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

           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:/.

       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 the IPC::Open3 manpage for an alternative that handles STDERR as
       well.  This function is really just a wrapper around open3().

3rd Berkeley Distribution    perl 5.005, patch 02                IPC::Open2(3)