trim string before character but still keep the remain part after it

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So I have this string which I have to trim and manipulate a little with it. My string example:

string test = "studentName_123.pdf";

Now, what I want to do is somehow extract only the _123 part and at the end I need to have studentName.pdf

What I have tried:

string test_extracted = test.Substring(0, test.LastIndexOf("_") )+".pdf";

This also works but the thing is that I don't want to add the ".pdf" suffix at the end of the string manually because I can have strings that are not pdf, for ex. studentName.docx , studentName.png. So basically I just want the "_123" part removed but still keep the remain part after that.

c#
4 Answers

I think this might help you:

        string test = "studentName_123.pdf";
        string test_extracted = test.Substring(0, test.LastIndexOf("_") )+ test.Substring(test.LastIndexOf("."),test.Length - test.LastIndexOf(".") );

Using Remove(int startIndex, int count):

        string test = "studentName_123.pdf";
        string test_extracted = test.Remove(test.LastIndexOf("_"), test.LastIndexOf(".") - test.LastIndexOf("_"));
user_100700070

Sounds like you mean something like this?

string extension = Path.GetExtension(test);
string pdfName = Path.GetFileNameWithoutExtension(test).Split('_')[0];
string fullName = pdfName + extension;
user_25995080

Since you know what value you will always be replacing in your strings, "_123", to base on your example, just utilize the replace method and replace it with nothing since the method expects two arguments;

string test_extracted = test.replace('_123', '');
user_173180040

This could be solved with a regular expression like this (\w*)_.*(\.\w*) where the first capture group (\w*) matches everything before the underscore and the second group (\.\w*) matches the file extensions.
Lastly we just have to concat the groups without the stuff inbetween like so:

string test = "studentName_123.pdf";
var regex = Regex.Match(test, @"(\w*)_.*(\.\w*)");
string newString = regex.Groups[1].Value + regex.Groups[2].Value;
user_84604360
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