in reply to regex logical equivalence?

The good thing about Perl regex is that you don't have to write the entire regex in one go, you can build it part by part programmatically. I often construct my regex in the maner as shown below to improve readability (at least to myself) and maintainability:
use strict; use warnings; # allowed prompt characters my $prompt_regex = '[>$%@~# ]'; # allowed characters in the prompt my $allowed_regex = '[\w@\-\.]*'; # a list of allowed prompt patterns my @patterns = ( '\[?' . $allowed_regex . $prompt_regex . '\]?', quotemeta '\\[\\e[0m\\] [0m', ); # build my regex dynamically my $regex = '(' . join('|',@patterns) .')\s?'; # test the regex print "regex: /$regex/\n\n"; while (<DATA>) { chomp; /$regex/ && printf "%-30smatched: %s\n", $_, $1; } __DATA__ blah crap crap [roger@www#] blah blah foo [] crap crap \[\e[0m\] [0m foo bar

And the output -
regex: /(\[?[\w@\-\.]*[>$%@~# ]\]?|\\\[\\e\[0m\\\]\ \[0m)\s?/ blah matched: crap crap matched: [roger@www#] blah blah foo matched: [roger@www#] [] crap crap matched: [] \[\e[0m\] [0m foo bar matched: \[\e[0m\] [0m