Question

I know what * is and what ? is.

However, I don’t understand what *? is. I know it’s used to make the “greedy” * operator a lazy one, but still, how does that read if * is zero or more times and ? is one or one time.

Thank you.

EDIT:
I underline the fact that I know what *, ?, greedy and lazy are.

Answer 1

This is a trick that has been used to extend regexp syntax without adding more special characters. Of course saying “zero or one” after “zero or more” has no meaning… so the combination *? should be read as a single token meaning “zero or more – not greedy”. In a similar way +? should be read as a single token meaning “one or more – not greedy”.

Greedyness never changes what strings are matched and what are not matched, but it may change what is the match found. For example group 1 of (AB*?)B+ matches A in ABBBBB, but group 1 of (AB*)B+ matches ABBBB in the same string.

The question mark in “strange places” has been used also in other special combinations that are available in several regexp engines, for example:

(?=...)     zero-width positive lookahead assertion
(?!...)     zero-width negative lookahead assertion
(?:...)     non-tagging group

as you see they all start with (? where clearly the question mark couldn’t mean “zero or one” (we’re at the beginning of an expression, zero or one of what?).