


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


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

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 connects 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 exception 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 your-
       self.

       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 normally 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 the waitpid entry in
       the perlfunc manpage 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,



2001-05-24                 perl v5.6.1                          1





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


       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 pro-
       cess, you can't control what it does with pipe buffering.
       Thus you can't just open a pipe to "cat -v" and continu-
       ally read and write a line from it.

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






































2001-05-24                 perl v5.6.1                          2


