while (1) {
    # Are we supposed to pause or stop?
    if (-E "/tmp/pause") {
        sleep 10;
        next;
    }
    last if -E "/tmp/STOP";

    # Find a file to process
    my @filist = glob("*.input");

    while (my $file = shift @filist) {
        # try to claim the file
        if (rename $file, "$file.working.$$") {
            # Successful, so go handle it
            process_file("$file.working.$$");
            last;
        }
        # Didn't get the file (someone else might've claimed it just
        # as we tried to), so just loop to the next one...
    }
 }