$pid = open3(\*WTRFH, \*RDRFH, \*ERRFH 'some cmd and args', 'optarg', ...);
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 instead of a pipe
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:/.
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 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.