CODEWITHSUNDEEP
c#regex
Josh
Josh

Reputation: 3611

How to specify to only match first occurrence?

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.

Upvotes: 34

Views: 62176

Answers (6)

womp
womp

Reputation: 116977

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.

Upvotes: 48

Diego
Diego

Reputation: 17

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();

Upvotes: 0

Tim Mahy
Tim Mahy

Reputation: 1319

Use grouping combined with RegExOptions.ExplicitCapture.

Upvotes: 0

Jeremy Ray Brown
Jeremy Ray Brown

Reputation: 1577

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();

Upvotes: 3

AJ.
AJ.

Reputation: 3102

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.

Upvotes: 0

Rich
Rich

Reputation: 36806

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.

Upvotes: 35

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