


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', ...);


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 '', or the same as
       RDRFH, then STDOUT and STDERR of the child are on the same
       file handle.  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 file handle.  In both cases, there
       will be a dup(2) instead of a pipe(2) made.

       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(), which means
       you'll have to use sysread() instead of normal stuff.

       open3() returns the process ID of the child process.  It
       doesn't return on failure: it just raises an exception
       matching /^open3:/.

WARNING
       It will not create these file handles for you.  You have
       to do this yourself.  So don't pass it empty variables
       expecting them to get filled in for you.

       Additionally, 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.








29/Apr/1999            perl 5.005, patch 03                     1





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



























































29/Apr/1999            perl 5.005, patch 03                     2


