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Regular expression capturing more than expected

New daddy so my eyes are tired and I'm trying to figure out why this code:

var regex = new Regex(@"(https:)?\/");
Console.WriteLine (regex.Replace("https://foo.com", ""));

Outputs:

foo.com

I only have one forward slash, so why were they both grouped for replacement?

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2 answers


Regex.Replace :

All strings that match the regular expression pattern with the specified replacement are replaced in the specified input line.



Each /

matches a regular expression pattern @"(https:)?\/"

. If you try eg. "https://foo/./com/"

, everything /

will be deleted.

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If you check what matches will be generated, it becomes clear. Add this to your code:

var matches = regex.Matches("https://foo.com");
foreach (Match match in matches)
{
    Console.WriteLine(match.Value);
}


And you will see what is https:/

matched and replaced, /

matched and replaced (since it https:

is optional) and foo.com

remains.

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