|Perl Monk, Perl Meditation|
IPC::Open3by tilly (Archbishop)
|on Sep 11, 2000 at 05:44 UTC ( #31831=modulereview: print w/replies, xml )||Need Help??|
Item Description: Open a process for reading, writing, and error handling
Review Synopsis: Very useful for fine-tuned control of launching processes
A basic Unix process starts life with a default place to read data from the outside world (STDIN), a default place to write data (STDOUT), a basic place to write errors to (STDERR), and some parent process who hopefully will be interested in how you died and will catch your return code (0 by default unless you exit or die).
Perl has many ways of starting processes. The most common are the following:
IPC::Open3 exports a function, open3. This allows you to start a command and choose what it gets for STDIN, STDOUT, and STDERR. For instance you might hand it for STDIN a filehandle reading from /dev/null to supress any attempts on its part to interact. You might want to keep track of STDERR for error reporting. Anything you want.
As with open, open3 returns the process ID. When the program should have exited you can then call wait or waitpid, check that you collected the right child, then look at $? for the return value.
For an example of real use of this, see Run commands in parallel. Another useful example that would make a good exercise is to write a function to run a process and surpresses all output unless the return-code is not zero in which case it prints an error message with information on the command, the return code, and what was printed to STDERR. (I use something like this for cron jobs.)