I've used a rename(1) utility^ that is apparently part of some Perl distribution. It's always been available on my Ubuntu systems and I haven't gone out of my way to install it. bar ⇒ baz would be something like: rename 's/\.bar$/.baz/' *.bar

You can dry-run first with `-n` flag if you're worried you didn't do it right, which is admittedly too possible. A bit more verbose, but a bit more powerful too.

^ http://manpages.ubuntu.com/manpages/trusty/man1/prename.1.ht...