Question

I have a string that can be either

"MyName (ctid 5555)"

or

"OtherName (id 555-5555-5555-555)"

I tried to write a regex to fetch ctid or id, like so:

"(?<=ctid=).+(?=))"

Checking here gave 0 results.

What’s wrong with my syntax?

Answer 1

Assuming that a ctid is always 4 digits, and an id is always 3-4-4-3 digits, and that either way it is enclosed in round brackets, I would do:

\((?:ctid (?<ctid>\d{4})|id (?<id>\d{3}-\d{4}-\d{4}-\d{3}))\)

This adds named groups and does validity checking at the same time. For example, you can use match.Groups['ctid'].value to get the ctid value, or ['id'] to get the id value. Because there is validity checking, you’ll never get (what I am assuming is) an invalid id like “(id 123)” (since it doesn’t have the 3-4-4-3 pattern).