Regex + Remove all text before match

Question

I\'m trying to figure out a way to remove all text in a string before match in Regex. I\'m coding this in C#.

For example, if the string is \"hello, test matching\

Answer 1

*Updated, using matchcollection

string test = "hello, test matching";

string regexStrTest;
regexStrTest = @"test\s\w+";       
MatchCollection m1 = Regex.Matches(test, regexStrTest);
//gets the second matched value
string value = m1[1].Value;   

Answer 2

For a simple solution, just replace "start-of-line anything test" with "test":

newString = Regex.Replace(oldString, "^.*test", "test");

Since * is greedy, this will replace as much as possible, i.e. a test b test c will become test c. To replace as little as possible, use *? instead of *.

If you want to avoid duplicating the search word, you can use a Zero-width positive lookahead assertion:

newString = Regex.Replace(oldString, "^.*(?=test)", "");

Answer 3

You can use positive lookahead to match a string but not capture it:

(?=test)

So you want to capture the stuff before the last occurrence of test:

^.*(?=test)

If you want to make it so that it is the first occurrence of test, use lazy matching:

^.*?(?=test)