How to specify to only match first occurrence?

Question

How can I specify to only match the first occurrence of a regular expression in C# using Regex method?

Here's an example:

string text = @"<link href=""/_layouts/OracleBI/OracleBridge.ashx?RedirectURL=res/sk_oracle10/b_mozilla_4/common.css"" type=""text/css"" rel=""stylesheet""></link></link>";
string pattern = @"(<link).+(link>)";
Regex myRegex = new Regex(pattern, RegexOptions.IgnoreCase);

Match m = myRegex.Match(text);   // m is the first match
while (m.Success)
{
    // Do something with m
    Console.Write(m.Value + "\n");
    m = m.NextMatch();              // more matches
}
Console.Read();

I would like this to only replace up to the first <\link>. And then also do the same for the rest of these matches.

Yes. I am trying to first understand how to get the first occurrence and then next would like to find each match and replace. Example: String str = "Hello this Hello Hello World"; String pattern = @"(H.+o)"; Regex re = new Regex(pattern, RegexOptions.IgnoreCase); String result = re.Replace(str, "Replacement"); Result of str: Replacement this Hello Hello World then: I would like to replace all occurrences of Hello with Replacement (I tried womps example below but it did not work). The whole thing is that I need to use complex regexs rather than jus replacing Hello with Replacment — Josh, Apr 13 '10 at 16:49
then: I would like to replace all occurrences of Hello with Replacement (I tried womps example below but it did not work). The whole thing is that I need to use complex regexs rather than just replacing Hello with Replacement — Josh, Apr 13 '10 at 16:50
@Josh - could you post the entire code by editing your question? We can analyze it a bit better that way. — womp, Apr 13 '10 at 17:06
@Josh - agh... you're parsing HTML with Regex? http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags — womp, Apr 13 '10 at 17:21

score 47 · Answer 1 · edited Nov 23 '17 at 06:25

47

Regex.Match(myString) returns the first match it finds.

Subsequent calls to NextMatch() on the resultant object from Match() will continue to match the next occurrences, if any.

For example:

  string text = "my string to match";
  string pattern = @"(\w+)\s+";
  Regex myRegex = new Regex(pattern, RegexOptions.IgnoreCase);

  Match m = myRegex.Match(text);   // m is the first match
  while (m.Success)
  {
       // Do something with m

       m = m.NextMatch();              // more matches
  }

EDIT: If you're parsing HTML, I would seriously consider using the HTML Agility Pack. You will save yourself many, many headaches.

edited Nov 23 '17 at 06:25

carla

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answered Apr 13 '10 at 16:15

womp

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this solution (with the addition of m = m.NextMatch();) still doesn't do the first match. Seems to find the last occurrence. – Josh Apr 13 '10 at 16:55
Here's an example: string text = @""; string pattern = @"()"; – Josh Apr 13 '10 at 17:04
Make sure you write **m =** `m.NextMatch()` in your loop or it will be infinite. – Saeb Amini Mar 04 '11 at 12:17
... speaking of parsing HTML with regex: http://stackoverflow.com/a/1732454/837703 – Jan 01 '15 at 00:09

score 35 · Accepted Answer · answered Apr 13 '10 at 17:19

I believe you just need to add a lazy qualifier on the first example. Whenever a wild card is "eating too much", you either need a lazy qualifier on the wild card or, in a more complicated scenario, look ahead. Add a lazy qualifier at the top (.+? in place of .+), and you should be good.

score 3 · Answer 3 · edited Jan 26 '12 at 16:41

string text = @"<link href=""/_layouts/OracleBI/OracleBridge.ashx?RedirectURL=res/sk_oracle10/b_mozilla_4/common.css"" type=""text/css"" rel=""stylesheet""></link></link>"; 
string pattern = @"(<link).+(link>)"; 
//Regex myRegex = new Regex(pattern, RegexOptions.IgnoreCase); 
//Match m = myRegex.Match(text);   // m is the first match
Match m = Regex.Match(text, pattern, RegexOptions.IgnoreCase);
/*while (m.Success)         
{             
    // Do something with m             
    Console.Write(m.Value + "\n");             
    m = m.NextMatch();              // more matches         
}*/
// use if statement; you only need 1st match
if (m.Success)
{
    // Do something with m.Value
    // m.Index indicates its starting location in text
    // m.Length is the length of m.Value
    // using m.Index and m.Length allows for easy string replacement and manipulation of text
}
Console.Read();

Also Regex.Match(input, pattern, Regex Options) will shorten your code — Jeremy Ray Brown, Aug 11 '11 at 20:14

score 0 · Answer 4 · answered Jul 04 '13 at 19:23

try this

string text = @"<link href=""/_layouts/OracleBI/OracleBridge.ashx?RedirectURL=res/sk_oracle10/b_mozilla_4/common.css"" type=""text/css"" rel=""stylesheet"">      </link></link>";
string pattern = @"(<link).+(link>)";
Regex myRegex = new Regex(pattern, RegexOptions.IgnoreCase);


MatchCollection matches = myRegex.Matches(text);
        foreach (Match m in matches) {
            Console.Write(m.Value + "\n");
        }
Console.Read();

score 0 · Answer 5 · edited Jan 26 '12 at 16:41

0

Use grouping combined with RegExOptions.ExplicitCapture.

edited Jan 26 '12 at 16:41

bluish

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answered Apr 13 '10 at 16:15

Tim Mahy

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score 0 · Answer 6 · edited May 23 '17 at 11:47

0

Maybe a little over-simplified, but if you get a collection of matches back and want to get the first occurrence you could look at the Match.Index property to find the lowest index.

Here's the MSDN documentation on it.

If it is just a scope issue, then I agree with Rich's comment - you need to use non-greedy modifiers to stop your expression from 'eating' too much.

edited May 23 '17 at 11:47

Community

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answered Apr 13 '10 at 17:19

AJ.

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How to specify to only match first occurrence?

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