As a beginner to Perl, maybe you shouldn't worry about what weird results split will give if you give it weird inputs. I bet most Perl experts would have to guess at what 'ab'=~/(a|b)+/ returns (although they would likely guess correctly). More important would be to learn how to use split properly.

• The regular expressions should identify the separator. In your case, it doesn't appear to be used to match a separator, so split is probably not the best tool for the job.

• You'll rarely want to use captures in a split pattern. When you do, what the captures match is returned in split's result.

• Using a quantifier on a capture doesn't make sense. If you want to group things in patterns, use (?:...) instead of (...). The latter is much slower since it remembers what the parens matched, and has side effects in split.