IPC::Open3(3pm) Perl Programmers Reference Guide IPC::Open3(3pm)

NAME
       IPC::Open3, open3 - open a process for reading, writing, and error han-
       dling

SYNOPSIS
           $pid = open3(\*CHLDIN, \*CHLDOUT, \*CHLDERR,
                           'some cmd and args', 'optarg', ...);

           my($wtr, $rdr, $err);
           $pid = open3($wtr, $rdr, $err,
                           'some cmd and args', 'optarg', ...);

DESCRIPTION
       Extremely similar to open2(), open3() spawns the given $cmd and con-
       nects CHLDOUT for reading from the child, CHLDIN for writing to the
       child, and CHLDERR for errors.  If CHLDERR is false, or the same file
       descriptor as CHLDOUT, then STDOUT and STDERR of the child are on the
       same filehandle.  The CHLDIN will have autoflush turned on.

       If CHLDIN begins with "<&", then CHLDIN will be closed in the parent,
       and the child will read from it directly.  If CHLDOUT or CHLDERR
       begins with ">&", then the child will send output directly to that
       filehandle.  In both cases, there will be a dup(2) instead of a pipe(2)
       made.

       If either reader or writer is the null string, this will be replaced by
       an autogenerated filehandle.  If so, you must pass a valid lvalue in
       the parameter slot so it can be overwritten in the caller, or an excep-
       tion will be raised.

       The filehandles may also be integers, in which case they are understood
       as file descriptors.

       open3() returns the process ID of the child process.  It doesn't return
       on failure: it just raises an exception matching "/^open3:/".  However,
       "exec" failures in the child are not detected.  You'll have to trap
       SIGPIPE yourself.

       Note if you specify "-" as the command, in an analogous fashion to
       "open(FOO, "-|")" the child process will just be the forked Perl
       process rather than an external command.  This feature isn't yet sup-
       ported on Win32 platforms.

       open3() does not wait for and reap the child process after it exits.
       Except for short programs where it's acceptable to let the operating
       system take care of this, you need to do this yourself.  This is nor-
       mally as simple as calling "waitpid $pid, 0" when you're done with the
       process.  Failing to do this can result in an accumulation of defunct
       or "zombie" processes.  See "waitpid" in perlfunc for more information.

       If you try to read from the child's stdout writer and their stderr
       writer, you'll have problems with blocking, which means you'll want to
       use select() or the IO::Select, which means you'd best use sysread()
       instead of readline() for normal stuff.

       This is very dangerous, as you may block forever.  It assumes it's
       going to talk to something like bbcc, both writing to it and reading from
       it.  This is presumably safe because you "know" that commands like bbcc
       will read a line at a time and output a line at a time.  Programs like
       ssoorrtt 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.

WWAARRNNIINNGG
       The order of arguments differs from that of open2().



perl v5.8.8                       2001-09-21                   IPC::Open3(3pm)