Regexp function to extract numbers

Regexp will not work if you are not looking for a specific pattern. If a specific pattern then yes, use Regexp.
There are many way to find integer value, as suggested by others. You can also try comparing with index of each element of your string/array. Choice should yours but based on your code performance. Thanks

Regexp will not work if you are not looking for a specific pattern. If a specific pattern then yes, use Regexp.
There are many way to find integer value, as suggested by others. You can also try comparing with index of each element of your string/array. Choice should yours but based on your code performance. Thanks

A lot of these examples appear to show a fundamental misunderstanding of regex. If you'd like to do this using regex, you can use:

fn!regexallmatches(
  "[0-9]+",
  "ABC 123"
)

Note that you'll have to choose between fn!regexallmatches and fn!regexfirstmatch depending on your data; the former returns a list of matches and the latter returns only the first match.

If you'd like to see and/or test regexes, this tool is an excellent option and (as per the link) allows you to share and test regexes.