C# Regex Pattern Conundrum

Question

I have a regex that I've verified in 3 separate sources as successfully matching the desired text.

But, when I use the regex in my code. It does not produce a match. I have used other regex with this code and they have resulted in the desired matches. I'm at a loss...

string SampleText = "starttexthere\r\nothertexthereendtexthere";
string RegexPattern = "(?<=starttexthere)(.*?)(?=endtexthere)";
Regex FindRegex = new Regex(@RegexPattern);
Match m = FindRegex.Match(SampleText);

I don't know if the problem is my regex, or my code.

Mike Dinescu · Accepted Answer · 2013-03-07 16:12:29Z

7

The problem is that your text contains a \r\n which means it is split across two lines. If you want to match the whole string you have to set the option to match across multiple lines, and to change the behavior of the . to include the \n (new-line character) in matched

 Regex FindRegex = new Regex(@RegexPattern, RegexOptions.Multiline | RegexOptions.Singleline);

edited Mar 7, 2013 at 16:12

answered Mar 7, 2013 at 15:55

Mike Dinescu

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3 Comments

s15199d Over a year ago

Tried that already. Regex.Match(SampleText, @RegexPattern, RegexOptions.Multiline).Groups[1].Value.ToString() returns an empty string

Mike Dinescu Over a year ago

what if you include the RegexOptions.Multiline | RegexOptions.Singleline as well

s15199d Over a year ago

Thanks Miky! It needed both Multiline and Singleline.

Cristian Lupascu · Accepted Answer · 2013-03-07 16:03:02Z

0

You don't need RegexOptions.Multiline.

The problem in your case is that the dot matches any character except line break characters (\r\ and \n).

So, you'll need to define your regex pattern like so: (?<=starttexthere)[\w\r\n]+(?=endtexthere) in order to specifically match text across line breaks.

Here's an online running sample: http://ideone.com/ZXgKar

answered Mar 7, 2013 at 16:03

Cristian Lupascu

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1 Comment

Cristian Lupascu Over a year ago

@s15199d yes, it does match. Also, the code in the ideone link works.

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