How to convert regexp from lookahead

Question

I have the following Regex in PHP and other code that is doing a great job.

/^(?:(?=[^ ]+\\d)(?:[A-Z0-9]+))|(?:[A-Z0-9]+) +?(?=.*\\d)(?:[A-Z0-9]+)?

Answer 1

Firstly, the left hand side of the alternation /^... matches nothing, because / can never appear before start of input.

That leaves just (?:[A-Z0-9]+) +?(?=.*\d), which can be expressed as:

((?:[A-Z0-9]+) ).*\d.*

The term " +?" as used is identical in effect to just " ".

Note however that this consumes more input than the original, which is unavoidable. Your original match is now in group 1.