正则表达式中的命名捕获组

Question

I need help with a regex to capture the numbers and hyphen from the following string: "some text and stuff 200-1234EM some other stuff"

It can also appear without the hypenated part: "some text 123EM other text"

I need either "200-1234" or "123" in a named capture group.

I tried this: \\b([0-9]{0,3}\\-{0,1}[0-9]{3})EM\\b

It does match, but it is not a named group.

When I try to name the group like this: \\b(?<test>[0-9]{0,3}\\-{0,1}[0-9]{3})EM\\b I get an error message "Unknown look-behind group near index 34"

I need this to work in the .NET RegEx class

Thanks!

Answer 1

resultString = Regex.Match(subjectString, @"\b(?<number>\d+(?:-\d+)?)EM\b").Groups["number"].Value;

This should do the trick. If you provide more input I could make it more robust.

Explanation:

    @"
\b            # Assert position at a word boundary
(?<number>    # Match the regular expression below and capture its match into backreference with name “number”
   \d            # Match a single digit 0..9
      +             # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
   (?:           # Match the regular expression below
      -             # Match the character “-” literally
      \d            # Match a single digit 0..9
         +             # Between one and unlimited times, as many times as possible, giving back as needed (greedy)
   )?            # Between zero and one times, as many times as possible, giving back as needed (greedy)
)
EM            # Match the characters “EM” literally
\b            # Assert position at a word boundary
"