How to get value from matching in grouping by name?

Question

    string input = "aaaabbbccc12345677XXXXsfsfsrfsd";
    MessageBox.Show(Regex.Match(input, "7(?<x1>.*)s").Groups["x1"].Value);

That Result

---

7XXXXsfsfsrf

OK

but i want XXXX Value Only HOW?

   MessageBox.Show(Regex.Match(input, ".*7(?<x1>.*?)s").Groups["x1"].Value);

Answer 1

"7(?<x1>.*)s"

You need to use the right syntax: Naming a group works like this (?<NameHere>ExpressionHere), see for example here or here.

Answer 2

You can ask your regex not to be too greedy

"7(?<x1>.*?)s"

Answer 3

Remember that regular expressions have longest-leftmost semantics. You seem to want the rightmost start with the leftmost end, so that's spelled

MessageBox.Show(Regex.Match(input, "^.*7(?<x1>.*?)s").Groups["x1"].Value);

The subpattern ^.*7 means “starting after the last 7 in the string…” Note that the caret (beginning of string) is redundant, but I like to use it for emphasis with ^.*x meaning the last x.

In contrast, .*? means match as few characters as possible, starting with none.