Looking for a specific regex

[Dennis Bork]

Hey all, I am a bit disappointed by myself to come up with that question, but hey! there are some regex cracks here that can easily answer this question and maybe deepen my understanding. I really tried to figure out the best regex for my problem - but I am new to programming and regex' still seem to make my head explode. Here's the string I've got:

Directory\Subdirectory\Subdir\Subsubdir\sub_sub_subv009\filename_with_lots_of_ABC123.txt

using this regex:

(?<=_)[a-zA-z0-9]*(?=.txt$)

I get:

of_ABC123

Close call, but what I need is just ABC123 - this are all characters as a string between the LAST '_' and ".txt" Additionally, I did this in Expresso (did not use the designer but did a lot of test runs to see if my regex matches) - will this be the regex to be used in C#? I really appreciate any hint to solve my last problem, Best Dennis

[Pete OHanlon]

First of all, if you have a regex question, there is a regular expression forum that should be used. Secondly, not every string manipulation requires a regex - a much simpler way would be to use string.LastIndexOf for the _ and IndexOf the . character and then just extract the substring from it.

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[savbace]

Here is an example of solution using both Regex and string class methods. In Regex I use a group with "FileCode" name to get result. As Pete said not all cases require using of Regex. And in this case I think would be better to use string methods (alternative variant).

        const string pattern = @"\_(?(\[^\_\]\[a-zA-Z0-9\])+)\\.txt$";
        const string text = @"Directory\\Subdirectory\\Subdir\\Subsubdir\\sub\_sub\_subv009\\filename\_with\_lots\_of\_ABC123.txt";

        var groupFileCode = Regex.Match(text, pattern);

        Console.WriteLine(groupFileCode.Groups\["FileCode"\].Value);

        // alternatively without regullar expressions
        int lastUnderscoreIndex = text.LastIndexOf('\_');
        int lastPointIndex = text.LastIndexOf('.');

        Console.WriteLine(text.Substring(lastUnderscoreIndex + 1, lastPointIndex - lastUnderscoreIndex - 1));

Regards, savbace

[lmoelleb]

Your range is [a-zA-z0-9] - notice the second "z" is lower case, and as "_" falls between uppercase A and lowercase z it is included in your match.

[Dennis Bork]

Thank you so much! I have overseen this. So I have at last understood a little bit of regex and did it right. Thank you also for the other answers, especially the C# code examples. I will try them tomorrow!

[thewazz]

for reference, my regex links: learn: http://www.guistuff.com/articles/regexp\_full\_1.html http://net.tutsplus.com/tutorials/javascript-ajax/you-dont-know-anything-about-regular-expressions/ online testing: http://refiddle.com/ http://www.gethifi.com/tools/regex http://gskinner.com/RegExr/

[PIEBALDconsult]

I'd likely use System.IO.Path.GetFileNameWithoutExtension to narrow it down first, then use LastIndexOf and Substring as others have suggested. Were I to use a Regex, I'd likely use _(?'Name'[^_\.]+)\. I prefer to use named groups to capture what I want. You may want to look at the RightToLeft option as well; very handy for getting stuff that follows other stuff. Oh, and I use this handy tool: RegexTester[^] :-D