>> Perl is certainly famous for its regex and popularizing thinking of problems in terms of regexes (for better or for worse), but it’s not the only game in town.

Agreed.

In that old system we did not have any TCL scripts or third-party libraries--just C, Perl, and C shell (no Bash; it was Unix).

C shell scripting is painful (https://www.grymoire.com/Unix/Csh.html), so practically all scripting was Perl or occasionally AWK.