I know I'm a bit late in the game, but putting that functionality
in cat(1) doesn't feel right. It's much too specialized (and besides,
locking a file that someone else opened (shell redirection) strikes
me as a wrong thing).

  I'd rather see a generic "wrap and lock" utility, much like env(1),
so one could do 

	wal -f /some/important/file -c /some/careless/program

  or whatever.

	mjl