I was worried someone would say that

What's to worry about? If you're concerned about having to keep an extra file around, consider locking the script itself. This may not be appropriate in all cases, but it's a fairly common idiom:

use Fcntl qw(:flock);

# lock myself
open my $lockfh, "<", $0
    or die "Cannot lock myself: $!\n";
flock $lockfh, LOCK_EX;

# ...

close $lockfh;
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