Here's a trick I thought up. Here's what your program should look like:

#!/usr/bin/perl

open MY_PID, "> /tmp/do_stuff.pid"
  or die "can't write to /tmp/do_stuff.pid: $!";
print MY_PID $$;
close MY_PID;

# rest of code
[download]

And here's what the cron should execute:

#!/usr/bin/perl

open PID, "/tmp/do_stuff.pid"
  or spawn();
chomp(my $pid = <PID>);
close PID;

kill -HUP => $pid or spawn();


sub spawn {
  fork and exit;
  exec "/usr/bin/perl", "my_prog.pl";
}
[download]

You know, you could make it even simpler. Just have the program create a file, and make sure the file gets deleted in an END { ... } block, so that, if the program stops, the file goes away. That's not 100% safe though, since the file could be deleted by something else. So nevermind, don't do that. Do the previous stuff instead. If you want to.

japhy -- Perl and Regex Hacker