Nice one, I'll try to counter this garbage GPT3 answer:

- I don't think the regex engine in Perl is implemented in Perl. It's probably implemented in C/C++, like grep. libpcre is in C anyway.

- Even if grep is/were more efficient, You might have consumed more time and energy thinking, typing and running "grep --only-matching --perl-regexp 'prefix \K\d+(?= suffix)'" than the suggested perl solution

- I might have consumed even more energy typing this reply. My computer is there, waiting for me typing, doing not much.

shorter version of the grep command is

    grep -oP 'prefix \K\d+(?= suffix)'

but yeah, I know it's easier to me because I did read man page at some point (while carefully avoiding perl manuals)

actually even that is not true, perldoc on regular expressions really helps even grep users

In all honesty, I'm more likely to remember this form than the Perl one, and once it's in the shell history, any will do anyway :-)