Question

I need some help on Regex. I need to find a word that is surrounded by whatever element, for example – *. But I need to match it only if it has spaces or nothing on the ether sides. For example if it is at start of the text I can’t really have space there, same for end.

Here is what I came up to

    string myString = "You will find *me*, and *me* also!";
    string findString = @"(\*(.*?)\*)";
    string foundText;
    MatchCollection matchCollection = Regex.Matches(myString, findString);
    foreach (Match match in matchCollection)
    {
        foundText = match.Value.Replace("*", "");
        myString = myString.Replace(match.Value, "->" + foundText + "<-");
        match.NextMatch();
    }
    Console.WriteLine(myString);

You will find ->me<-, and ->me<- also!

Works correct, the problem is when I add * in the middle of text, I don’t want it to match then.

Example: You will find *m*e*, and *me* also!
Output: You will find ->m<-e->, and <-me* also!

How can I fix that?

Answer 1

Try the following pattern:

string findString = @"(?<=\s|^)\*(.*?)\*(?=\s|$)";

• (?<=\s|^)X will match any X only if preceded by a space-char (\s), or the start-of-input, and
• X(?=\s|$) matches any X if followed by a space-char (\s), or the end-of-input.

Note that it will not match *me* in foo *me*, bar since the second * has a , after it! If you want to match that too, you need to include the comma like this:

string findString = @"(?<=[\s,]|^)\*(.*?)\*(?=[\s,]|$)";

You’ll need to expand the set [\s,] as you see fit, of course. You might want to add !, ? and . at the very least: [\s,!?.] (and no, . and ? do not need to be escaped inside a character-set!).

EDIT

A small demo:

string Txt = "foo *m*e*, bar";
string Pattern = @"(?<=[\s,]|^)\*(.*?)\*(?=[\s,]|$)";
Console.WriteLine(Regex.Replace(Txt, Pattern, ">$1<"));

which would print:

>m*e<