How to use preg_match to extract data?

Question

I am pretty new to the use of preg_match. Searched a lot for an answer before posting this question. Found a lot of posts to get data based on youtube ID etc. But nothing as

Answer 1

One solution is:

\[#(\d+)\]

This matches the left square bracket and pound sign [#, then captures one or more digits, then the closing right square bracket ].

You would use it like:

preg_match( '/\[#(\d+)\]/', '[#1234] Subject', $matches);
echo $matches[1]; // 1234

You can see it working in this demo.