.Net正则表达式是否有小写表达式？

Question

Perl has the \\u operator to lowercase a match when using string replacement and regular expressions. Does .Net have anything similar? For example, uppercase all words that start with a <

s/<\(\w*\)/<\U\1/

Answer 1

The way to do these kind of things in .NET is using the MatchEvaluator parameter:

string pattern = @"<(\w*)";
string replaced = Regex.Replace(line, pattern, 
                  x => "<" + x.Groups[1].ToString().ToUpper());     

This reads: Whenever you find the regular expression, replace it with the first group uppercased.

Answer 2

You've got some errors in your Perl code. In both Perl and .NET regexes, \\( and \\) match the literal characters, ( and ) ; to use parentheses as grouping operators, leave the backslashes off. Also, \\u\u003c/code> does not lowercase a match , it titlecases (usually the same as uppercasing) the next character . What you're thinking of is \\L , which lowercases all characters until the end of the string or \\E , whichever comes first.

In Perl, \\U , \\L and such aren't really a regex feature, they're a string feature, like the more common escape sequences: \\n , \\t , etc.. They're listed redundantly in the regex docs because they're especially useful in regex substitutions. C# has no equivalent for them, either in string literals or the regex classes, but as @steinar pointed out, it does have MatchEvaluator and (since .NET 3.0) lambda expressions:

string s = "ABC<XYZ!";
Console.WriteLine(Regex.Replace(s, @"<(\w+)", m => m.Value.ToLower()));

output:

ABC<xyz!

edit: The parentheses aren't really necessary in my example, but I left them in to demonstrate their proper use as grouping operators. I also changed the original \\w* to \\w+ ; there's no point matching zero word characters when your only goal is to change the case of word characters.