($txt = '123abc') =~ /(a|b|c)/; 1. ^123abc - check for a -> fail - check for b -> fail - check for c -> fail 2. 1^23abc - check for a -> fail - check for b -> fail - check for c -> fail 3. 12^3abc - check for a -> fail - check for b -> fail - check for c -> fail 4. 123^abc - check for a -> succeess, $1 becomes 'a'