How can I run a system command in Perl asynchronously?

Question

I currently have a Perl script that runs an external command on the system, gathers the output, and performs some action based on what was returned. Right now, here is how I run this (where $cmd is a string with the command setup):

@output = `$cmd`;

I'd like to change this so if the command hangs and does not return a value after so much time then I kill the command. How would I go about running this asynchronously?

Answer 1

There's a LOT of ways to do this:

• You can do this with a fork (perldoc -f fork)
• or using threads (perldoc threads). Both of these make passing the returned information back to the main program difficult.
• On systems that support it, you can set an alarm (perldoc -f alarm) and then clean up in the signal handler.
• You can use an event loop like POE or Coro.
• Instead of the backticks, you can use open() or respectively open2 or open3 (cf. IPC::Open2, IPC::Open3) to start a program while getting its STDOUT/STDERR via a file handle. Run non-blocking read operations on it. (perldoc -f select and probably google "perl nonblocking read")
• As a more powerful variant of the openX()'s, check out IPC::Run/IPC::Cmd.
• Probably tons I can't think of in the middle of the night.