Hi, I'm relatively new to perl programming, and I couldn't find an answer to this on perldoc (maybe I didn't know what to search for). I need to invoke a long-running shell script from a perl script, and the perl script needs to know the shell script's PID so that it can send it signals later. The shell script does a bunch of stuff and then sits in a sleep loop waiting for signals from the perl script.

I would like to execute the shell script as an independent process (i.e. fork then exec), and I don't want the perl script to wait for the shell script to exit before continuing, because it never will (until the perl script sends the right signal). As far as I can tell, the system() function doesn't do the right thing (waits for child to exit), neither does exec() (never returns), and I don't think qx/backticks would work either for the same reason as with system().

Assuming I can execute a shell script "in the background" and continue execution, I then need to get the PID of the child process. How do I do that? I know perl reserves $$ for the PID of the perl script and offers a getppid() function to get the parent PID, but how do I get the child PID?

In case I'm not being clear, this is what I want to do in shell syntax: 

my_script.sh &
pid=$!

[download]

Of course, $! means something completely different in perl. I'm sure this is a not-so-uncommon programming task, so how do I do it?

In reply to start process in bg, get child PID by butters

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