Re: Multiple commands with one system call

[jethro]

One simple way to start more than one program simultaneously (on linux) is to use the shell to execute them in the background. I.e.

system("program1 &");
system("program2 &");

would run both programs concurrently, the last one wouldn't even need to run in the background. Programs in the background should not do any screen IO because they are detached from the terminal screen. But you can redirect output to files or /dev/null if that output is uniteresting

Another possibility is to use open with a pipe, i.e. open($f,"-|","program1"); which would enable you to get further input over STDIN to the program.

A third possibility is to use fork to do the (implicit) forking done by the previous methods yourself. And probably the very best possibility is to let a module like Parallel::ForkManager handle most of that work.

[renzosilv]

Hey!

I had tried using the system call with the "&" sign but the problem with that is that I also need to know when this program is closed by the user so I can run clean up commands. When I make a regular system call I can just run my clean up commands after because they won't be run until after the program is closed.

Is there an easy way for me to catch when this program is being closed ?

Thanks again for all your help.

[TomDLux]

It's worth considering whether you need this degree of control, or whether it would be enough to do something simpler...say, run a job once an hour automatically.

If you need this degree of control and interactivity, I would have a wrapper script which launches your program, storing the process id (PID ) of the process. Then at regular intervals it can verify the process is still running, using ps. When the process stops, the wrapper can send a message.

A simple way to indicate the status is to create an indicator file, and delete it at the end. You can 'touch' the file at intervals to demonstrate the process is running and not crashed. Alternate, using the open with a pipe strategy, you can send text messages at intervals, 'still running', 'crashed' or 'completed'.

[zentara]

Is there an easy way for me to catch when this program is being closed ?

You might look at IPC::System::Simple , it makes collecting return values simple. Read the Advanced Synopsis for examples.

[jethro]

Sure, lots of ways. For example instead of calling your program you could call a wrapper script that calls your program and on exit creates a file/appends to a file/touches a file. This can be detected by your script

#!/bin/sh
# wrapper script

program1

touch /tmp/finishedwith$1

You could call this from perl with a random number as parameter (the $1) so that each finish would create a different file. In the perl script you would monitor for the existance of this file

This is easy but not very clean and safe. Another way is to use fork instead of system, because fork tells you the process id of the newly created process. And you can wait() for the process to finish (which would block your script) or check if the process is still running (somehow ;-).

But really, look at Parallel::ForkManager, all the functions you want are already there. With "run_on_finish" you can choose a subroutine that is called when the process finishes.