How to use named groups when performing a Regex.Replace()

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.

Kendall Frey · Accepted Answer · 2012-10-18 19:29:58Z

133

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.

edited Oct 18, 2012 at 19:29

answered Oct 18, 2012 at 19:21

Kendall Frey

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1 Comment

Shimmy Weitzhandler Over a year ago

How can I replace a named group with some other value while keeping the rest of the string intact?

Josh M. · Accepted Answer · 2013-01-22 19:42:09Z

20

Simply replace with ${groupName}

[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, "${secondMatch} ${firstMatch}");
    Assert.AreEqual(expected, replace);
}

edited Jan 22, 2013 at 19:42

Josh M.

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answered Oct 18, 2012 at 19:24

CaffGeek

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