IPC::Open3(3p) Perl Programmers Reference Guide IPC::Open3(3p)NAME
IPC::Open3, open3 - open a process for reading, writing, and
error handling
SYNOPSIS
$pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR,
'some cmd and args', 'optarg', ...);
my($wtr, $rdr, $err);
$pid = open3($wtr, $rdr, $err,
'some cmd and args', 'optarg', ...);
DESCRIPTION
Extremely similar to open2(), open3() spawns the given $cmd
and 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 filehan-
dle. 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
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 process 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 normally as simple as calling "wait-
pid $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.
perl v5.8.8 2005-02-05 1
IPC::Open3(3p) Perl Programmers Reference Guide IPC::Open3(3p)
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 writ-
ing 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 v5.8.8 2005-02-05 2
