regex - Regular Expression to find a string included between two characters while EXCLUDING the delimiters

Question

I need to extract from a string a set of characters which are included between two delimiters, without returning the delimiters themselves.

A simple example should be helpful:

Target: extract the substring between square brackets, without returning the brackets themselves.

Base string: This is a test string [more or less]

If I use the following reg. ex.

[.*?]

The match is [more or less]. I need to get only more or less (without the brackets).

Is it possible to do it?

Answer 1

Easy done:

(?<=[)(.*?)(?=])

Technically that's using lookaheads and lookbehinds. See Lookahead and Lookbehind Zero-Width Assertions. The pattern consists of:

• is preceded by a [ that is not captured (lookbehind);
• a non-greedy captured group. It's non-greedy to stop at the first ]; and
• is followed by a ] that is not captured (lookahead).

Alternatively you can just capture what's between the square brackets:

[(.*?)]

and return the first captured group instead of the entire match.