IPC::Open3

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



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

SYNOPSIS
	   $pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR,
			   ’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 CHLD_OUT for reading from the child, CHLD_IN for writing to the
       child, and CHLD_ERR for errors.	If CHLD_ERR is false, or the same
       file descriptor as CHLD_OUT, then STDOUT and STDERR of the child are
       on the same filehandle.	The CHLD_IN will have autoflush turned on.

       If CHLD_IN begins with "<&", then CHLD_IN will be closed in the par-
       ent, and the child will read from it directly.  If CHLD_OUT or
       CHLD_ERR 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
       exception will be raised.

       The filehandles may also be integers, in which case they are under-
       stood 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 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 informa-
       tion.

       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.	Pro-
       grams 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 v5.8.8			  2001-09-21			IPC::Open3(3)