How to extract a value from a string using regex and a shell?

Question

I am in shell and I have this string: 12 BBQ ,45 rofl, 89 lol

Using the regexp: \\d+ (?=rofl), I want 45 as a result.

Answer 1

You can do this with GNU grep's perl mode:

echo "12 BBQ ,45 rofl, 89 lol"|grep -P '\d+ (?=rofl)' -o

-P means Perl-style, and -o means match only.