|manpages.info - online man pages|
IPC::Open2, open2 - open a process for both reading and writing
$pid = open2(\*RDRFH, \*WTRFH, 'some cmd and args'); # or without using the shell $pid = open2(\*RDRFH, \*WTRFH, 'some', 'cmd', 'and', 'args');
# or with handle autovivification my($rdrfh, $wtrfh); $pid = open2($rdrfh, $wtrfh, 'some cmd and args'); # or without using the shell $pid = open2($rdrfh, $wtrfh, 'some', 'cmd', 'and', 'args');
The open2() function runs the given $cmd and connects $rdrfh for reading and $wtrfh for writing. It's what you think should work when you try
$pid = open(HANDLE, "|cmd args|");
The write filehandle will have autoflush turned on.
If $rdrfh is a string (that is, a bareword filehandle rather than a glob
or a reference) and it begins with
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.
open2() returns the process ID of the child process. It doesn't return on
failure: it just raises an exception matching
open2() 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
This whole affair is quite 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
The IO::Pty and Expect modules from CPAN can help with this, as they provide a real tty (well, a pseudo-tty, actually), which gets you back to line buffering in the invoked command again.
The order of arguments differs from that of open3().
See IPC::Open3 for an alternative that handles STDERR as well. This function is really just a wrapper around open3().