Question

I am having trouble capturing parentheses.

I have a big file with data of this form:

I.u[12] = {n: "name1",...};
I.u[123] = {n: "name2",...};
I.u[1234] = {n: "name3",...};

I want to create a system which helps me get the name (here name1, name2, name3) out of the file if I provide the id (here 12, 123, 1234). I have the following code:

    public static string GetItemName(int id)
    {
        Regex regex = new Regex(@"^I.u\["+id+@"\]\s=\s{n:\s(.+),.+};$");
        Match m= GetMatch(regex,filepath);
        if(m.Success) return m.Groups[0].Value;
        else return "unavailable";
    }

    public static Match GetMatch(Regex regex, string filePath)
    {
        Match res = null;
        using (StreamReader r = new StreamReader(filePath))
        {
            string line;
            while ((line = r.ReadLine()) != null)
            {
                res = regex.Match(line);
                if (res.Success) break;
            }
        }
        return res;
    }

The regex finds the correct line in the file but I really don’t know why it doesn’t extract the name as I wanted and,

if(m.Success) return m.Groups[0].Value;

returns me the whole line in the file and not the name… I tried a lot of things, even changing m.Groups[0] to m.Groups[1] but it didn’t work.

I have searched for a moment now without success. Would you have an idea of what is wrong?

Answer 1

Based on your updated question, I can see that you are using a greed quantifier: .+. This will match as much as possible. You want a passive modifier, which will only match as much as necessary: .+?

Try this:

Regex regex = new Regex(@"^I.u\["+id+@"\]\s=\s\{n:\s(?<Name>.+?),.+\};$", RegexOptions.Multiline);

Then:

if(m.Success) return m.Groups["Name"].Value;