Question

I’m sure this is simple and I’ll probably be embarrassed to have this question in my profile but I can’t seem to get this Regex correct.

I’m tring to extract just the digits from the last group of the following string:

Properties[1].Securitymeasures[14].AdditionalSecurityType

so I want to have a regex that will return 14

The Regex I have come up with is:

\[(\d)+\]

However – the match is returning “[14]” – including the brackets and I do not understand why. I have surrounded the \d with parenthesis which should mean that this is the data I want to capture.

Answer 1

Well, your regex is actually matching

1. An opening bracket
2. One or more consecutive digits
3. A closing bracket

So the fact that it returns the brackets is entirely correct. If you debug the following

Regex.Match("Properties[1].Securitymeasures[14].AdditionalSecurityType",
            @"\[(\d)+\]")
     .Groups[1]
     .Value // equals '1'

You’ll see that the \d is captured as a group (you put it in parens, after all).

What you want to do is use a “Positive Lookbehind” to specify that you are looking for one or more digits after a bracket.

(?<=\[)\d+

that says

1. Match one or more consecutive digits
2. That come immediately after an open bracket

You can bracket that with a Positive Lookahead, but if you are parsing integer indexes, then you can always expect there to be only digits within brackets and can skip the lookahead.