IPC::Open3, open3 - open a process for reading, writing, and error handling
$pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR, some cmd and args, optarg, ...);
my($wtr, $rdr, $err); $pid = open3($wtr, $rdr, $err, some cmd and args, optarg, ...);
Extremely similar to open2(), open3() spawns the given $cmd and connects 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 parent, 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 understood as file descriptors.
open3() returns the process ID of the child process. It doesnt return on failure: it just raises an exception matching /^open3:/. However, exec failures in the child are not detected. Youll 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 isnt yet supported on Win32 platforms.
open3() does not wait for and reap the child process after it exits. Except for short programs where its 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 youre 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 childs stdout writer and their stderr writer, youll have problems with blocking, which means youll want to use select() or the IO::Select, which means youd best use sysread() instead of readline() for normal stuff.
This is very dangerous, as you may block forever. It assumes its 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 dont have control over source code being run in the child process, you cant control what it does with pipe buffering. Thus you cant just open a pipe to cat -v and continually read and write a line from it.
The order of arguments differs from that of open2().
|perl v5.8.8||IPC::Open3 (3pm)||2001-09-21|