正则表达式匹配句子的第二个单词并修剪前导空格

Question

I'm trying to write a regex that matches the second word of a sentence.

What I have so far is

\s+[^\s]+

Which matches

The quick brown fox jumps over the lazy dog

Unfortunately I can't come up with a solution that removes the leading white space.

For an example see http://regex101.com/r/nB9yD9

So, is there an easy way to match just "quick" without the white space? The weapon of choice here is C#, if it makes any difference.

And it HAS to be regex, I know String.Split would be much nicer in this specific situation.

On a side note, is it possible to match the n-th word of sentence in regex? For what I know regex can't group into a unknown number of groups, is that correct?

EDIT : I had a typo in the example. The underscore I put there was meant to highlight the white space.

Answer 1

The regular expression you are using is correct. To go around your problem, you could use capture groups , something like so:

        string str = "The quick brown fox jumps over the lazy dog";
        Regex r = new Regex(@"\s+([^\s]+)");
        Match m = r.Match(str);
        System.Console.WriteLine(m.Groups[1]);

This will yield quick , without the trailing space.

Alternatively, you could use the trim() method on your result as well.

Also, as per your side note, you can match the nth word of a given sentence by combining C# and regex, something like so should do what you need:

        string str = "The quick brown fox jumps over the lazy dog";
        Regex r = new Regex(@"(^|\s)+([^\s]+)");
        MatchCollection mc = r.Matches(str);                        
        for (int i = 0; i < mc.Count; i++)
        {
            System.Console.WriteLine(mc[i].Groups[2]);
        } 

Yields:

The
quick
brown
fox
jumps
over
the
lazy
dog

I had to make amendments to the regex to take in consideration the first word as well. This allows the regex to pick words which are either preceeded by a white space or else, the beginning of the string.

As per your comment, please take a look at this link.

Answer 2

string str = "The quick brown fox jumps over the lazy dog";
Regex r = new Regex(@"\w+");  //Find words

MessageBox.Show(r.Matches(str)[1].Value); // Get all words and show value at 1st position