• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) with your changes locally?

brew list <name> outputs all files in Cellar and hits Ruby code making it slow to run in a bash script. Could possibly use brew list --formula | grep <name> but that has more overhead than just a directory check while doing essentially the same check.

For example, when checking ruby command (with ruby formula installed), this is a 10x difference (5s vs 0.5s):

Before:

❯ time (brew which-formula --skip-update --explain ruby)
The program 'ruby' can be found in the following formulae:
  * jruby
  * portable-ruby
  * ruby@3.1
  * ruby@3.2
  * ruby@3.3
Try: brew install <selected formula>
( brew which-formula --skip-update --explain ruby; )  3.16s user 1.73s system 93% cpu 5.246 total

After:

❯ time (brew which-formula --skip-update --explain ruby)
The program 'ruby' can be found in the following formulae:
  * jruby
  * portable-ruby
  * ruby@3.1
  * ruby@3.2
  * ruby@3.3
Try: brew install <selected formula>
( brew which-formula --skip-update --explain ruby; )  0.25s user 0.15s system 73% cpu 0.545 total