Programming Perl, 3rd Edition

IPC::Open3

use IPC::Open3;

local(*HIS_IN, *HIS_OUT, *HIS_ERR);

$childpid = open3(*HIS_IN, *HIS_OUT, *HIS_ERR, $cmd, @args);
print HIS_IN "stuff\n";
close(HIS_IN);            # Give end of file to kid.
@outlines = <HIS_OUT>;    # Read till EOF.
@errlines = <HIS_ERR>;    # XXX: block potential if massive
print "STDOUT:\n", @outlines, "\n";
print "STDERR:\n", @errlines, "\n";
close HIS_OUT;
close HIS_ERR;
waitpid($childpid, 0);
if ($?) {
    print "That child exited with wait status of $?\n";
}

The IPC::Open3 module works like IPC::Open2 (the latter is implemented in terms of the former), except that open3 provides access to the standard input, the standard output, and the standard error handles of the program you launch. The same caveats apply as with open2 (see the previous entry), plus a few more. The order of arguments is different in open3 than with open2. Instead of passing the handle to read from first and the handle to write to second, this time it's the other way around. Also, with open3, danger of deadlock is even greater than before. If you try to read through end-of-file on one of the child's two output handles, but meanwhile there's a great deal of output on the other handle, the peer process blocks and appears to hang. Use either the four-argument form of select or the standard IO::Select module to circumvent this. See Chapter 16 for more details.