Question

How do I use named captures when performing Regex.Replace? I have gotten this far and it does what I want but not in the way I want it:

[TestCase("First Second", "Second First")]
public void NumberedReplaceTest(string input, string expected)
{
    Regex regex = new Regex("(?<firstMatch>First) (?<secondMatch>Second)");
    Assert.IsTrue(regex.IsMatch(input));
    string replace = regex.Replace(input, "$2 $1");
    Assert.AreEqual(expected, replace);
}

I want to match the two words with named captures and then use the (named) captures when performing the replace.

Answer 1

Instead of "$2 $1", you can use "${secondMatch} ${firstMatch}".

There is a list of all the replacements you can do here.

Here is an abbreviated list:

$number – The captured group by number.

${name} – The captured group by name.

$$ – $ literal.

$& – Entire match.

$` – The input string before the match.

$’ – The input string after the match.

$+ – The last group captured.

$_ – The entire input string.