Regex to change text case

Question

I want to replace the text between the tags upcase to its uppercase version. Is there a way to do it by only using Regex.Replace method? (without using IndexOf)

Below is the code I was trying:

string texto = "We are living in a <upcase>yellow submarine</upcase>. We don't have <upcase>anything</upcase> else.";                
Console.WriteLine(Regex.Replace(texto, "<upcase>(.*)</upcase>", "$1".ToUpper()));

The expected result is:

We are living in YELLOW SUBMARINE. We don't have ANYTHING else.

but I get:

We are living in yellow submarine. We don't have anything else.

Answer 1

I would do like,

string str = "We are living in a <upcase>yellow submarine</upcase>. We don't have <upcase>anything</upcase> else.";
string result = Regex.Replace(str, "(?<=<upcase>).*?(?=</upcase>)",  m => m.ToString().ToUpper());
Console.WriteLine(Regex.Replace(result, "</?upcase>", ""));

Output:

We are living in a YELLOW SUBMARINE. We don't have ANYTHING else.

IDEONE

Explanation:

• (?<=<upcase>).*?(?=</upcase>) - Matches the text which was present inbetween <upcase> ,</upcase> tags. (?<=...) called positive lookbehind assertion, here it asserts that the match must be preceded by <upcase> string. (?=</upcase>) called positive lookahead which asserts that the match must be followed by </upcase> string. So the second line of code changes all the matched characters to uppercase and stores the result to the result variable.

• /? optional / (forward slash). So the third line of code replaces all the <upcase> or </upcase> tags present in the result variable with an empty string and prints the final output.