正则表达式提取匹配组

Question

(50798.3 vol 1 of 14-page 113)

The above is my clipboard content. As in my previous question , I extracted 50798.3 vol 1 of 14 and saved it in pdf_name and 113 as pagenumber. This worked well.

            var current_clipboard = Clipboard.GetText();
            var regEx = @"^\((?<Desc>[^-]*)-page\s(?<Page>\d+)";
            var match = Regex.Match(current_clipboard, regEx);
            string pdf_name = match.Groups["Desc"].Value;
            string pagenumber = match.Groups["Page"].Value;

Now, for a variation of the clipboard content where the -page would be of the format _Page or _Pages, I have used the below and it is not working. By not working, I mean when I use MessageBox.Show for pdf_name and pagenumber, the message box is displaying blank messages. Also, when I test the RegEx, it is showing 3 groups as here . I don't need the second match group.

            var current_clipboard = Clipboard.GetText();
            var regEx = @"^\((?<Desc>[^-]*)_pag(e|es)\s(?<Page>\d+)";
            var match = Regex.Match(current_clipboard, regEx);
            string pdf_name = match.Groups["Desc"].Value;
            string pagenumber = match.Groups["Page"].Value;

So, I am doing something wrong. Please help me save the correct values to pdf_name and pagenumber.

Edit#

@Jerry

I tried your version as below.

            var current_clipboard = Clipboard.GetText();
            var regEx = @"^\((?<Desc>[^-]*)_pages?\s(?<Page>\d+)";
            var match = Regex.Match(current_clipboard, regEx);
            string pdf_name = match.Groups["Desc"].Value;
            string pagenumber = match.Groups["Page"].Value;
            MessageBox.Show(pdf_name);
            MessageBox.Show(pagenumber);

Unfortunately the message box is returning blank messages.

Answer 1

The issue seems to be that, given you no longer have a - separator before your pages, your initial [^-]* pattern is gobbling up your whole string.

If underscores don't appear in your description, you should replace [^-]* with [^_]* . Alternatively, use lazy matching: (?<Desc>.*?) .

Answer 2

You're capturing (e|es) as the 2nd group.

Change it to a non-capturimg group

(?:e|es)

Non-Capturing Groups: (?: Often, you need parentheses in order to write an expression that makes sense. Normally, parentheses capture what they match. Non-capturing groups allow you to use parentheses without capturing anything. Watch out, as the syntax closely resembles that for a lookahead.

Non-Capturing Group Pattern: (?:Bob) Matches Bob, but Bob is not captured.

http://www.rexegg.com/regex-disambiguation.html

Answer 3

Regex are by default, case sensitive, meaning that p will match only p and not P . If you want a case insensitive regex, then you can either use the RegexOptions.IgnoreCase or the inline modifier (?i) , or you use [Pp] in your regex, which will match either p or P (but the other letters will be match in a case sensitive manner.

With the option, the line with .Match will change:

var match = Regex.Match(current_clipboard, regEx, RegexOptions.IgnoreCase);

With the inline modifier, the regex will change:

var regEx = @"(?i)^\((?<Desc>[^-]*)_pag(e|es)\s(?<Page>\d+)";

With the character class, the regex will change:

var regEx = @"^\((?<Desc>[^-]*)_[Pp]ag(e|es)\s(?<Page>\d+)";

To your next issue, the basic way to avoid a capture is to use a non-capture group. Here, you have (e|es) which is a capture group. Change that to (?:e|es) :

var regEx = @"^\((?<Desc>[^-]*)_[Pp]ag(?:e|es)\s(?<Page>\d+)";

Though really, you don't need an alternation here. You can use the ? quantifier meaning 0 or 1 times:

var regEx = @"^\((?<Desc>[^-]*)_[Pp]ages?\s(?<Page>\d+)";

---

Example with the option and ? quantifier:

var current_clipboard = Clipboard.GetText();
var regEx = @"^\((?<Desc>[^-]*)_pages?\s(?<Page>\d+)";
var match = Regex.Match(current_clipboard, regEx, RegexOptions.IgnoreCase);
string pdf_name = match.Groups["Desc"].Value;
string pagenumber = match.Groups["Page"].Value;

And here 's another regex tester site that supports this syntax for named capture groups.