System Programming in Perl

Useful file locking utility

        #!/usr/bin/perl

        use Fcntl ':flock';

        die "Usage: with-lock lockfile command [args...]\n"
          unless @ARGV;

        my ($semaphore, $cmd, @args) = @ARGV;
        open my($sem), "+<", $semaphore
          or die "Couldn't open semaphore '$semaphore': $!\n";
        if (flock $sem, LOCK_EX) {
          system($cmd, @args);
        }