Regex - split by "_" and exclude file extension

user_15045775 0
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I need to split the following string AAA_BBB_CCC.extension by "_" and exclude from the results any file extension. Where A, B and C can be any character or space. I wish to get AAA, BBB and CCC.

I know that \.(?:.(?!\.))+$ will match .extension but I could not combine it with matching "_" for splitting.

regex c#
3 Answers

Use the Path.GetFileNameWithoutExtension function to strip the extension from the file name.

Then use String.Split to get an array with three items:

var fileName = Path.GetFileNameWithoutExtension(fullName);
var parts = fileName.Split('_');
var partAAA = parts[0];
var partBBB = parts[1];
var partCCC = parts[2];

If the parts are always the same fixed number of characters long, you can as well extract them using the Substring function. No need to resort to regex here.

user_11323340

Another option is to make use of the .NET Group.Captures property and capture any char except an _ in a named capture group, which you can extract from the match using a named group.

^(?'val'[^_]+)(?:_(?'val'[^_]+))+\.\w+$

Explanation

  • ^ Start of string
  • (?'val'[^_]+) Named group val, match 1+ chars other than _ using a negated character class
  • (?: Non caputure group
    • _(?'val'[^_]+) Match an _ and capture again 1+ chars other than _ in same named group val
  • )+ Close the non capture group and repeat 1+ times for at least 1 occurrence with _
  • \.\w+ Match a . and 1+ word chars
  • $ End of string

Regex demo

string pattern = @"^(?'val'[^_]+)(?:_(?'val'[^_]+))+\.\w+$";
string input = @"AAA_BBB_CCC.extension";            
Match m = Regex.Match(input, pattern);
foreach (Capture capture in m.Groups["val"].Captures) {
   Console.WriteLine(capture.Value);
}

Output

AAA
BBB
CCC

enter image description here

user_54249880

If you wanted to use a regex based approach here, you could try doing a find all on the following regex pattern:

[^_]+(?=.*\.\w+$)

This pattern will match every term in between underscore, except for the portion after the extension, which will be excluded by the lookahead.

Regex rx = new Regex(@"[^_]+(?=.*\.\w+$)");
string text = "AAA_BBB_CCC.extension";
MatchCollection matches = rx.Matches(text);
foreach (Match match in matches)
{
    Console.WriteLine(match.Groups[0].Value);
}

This prints:

AAA
BBB
CCC
user_18632290
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