IPC::Open3

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



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

SYNOPSIS
           $pid = open3(\*WTRFH, \*RDRFH, \*ERRFH,
                           '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 RDRFH for reading, WTRFH for writing, and ERRFH for errors.  If
       ERRFH is false, or the same file descriptor as RDRFH, then STDOUT and
       STDERR of the child are on the same filehandle.  The WTRFH will have
       autoflush turned on.

       If WTRFH begins with "<&", then WTRFH will be closed in the parent, and
       the child will read from it directly.  If RDRFH or ERRFH 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 pro-
       cess rather than an external command.  This feature isn't yet supported
       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 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.

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



perl v5.8.6                       2001-09-21                     IPC::Open3(3)