C# regex - not matching my string

Question

I'm using NET 2.0 with WinForms on C#. I am having a big problem with regex. I'm trying to add a colon to 4 or more letter words in a simple string. It should only append the colon once, after that the code shouldn't append any more.

Regex lbls = new Regex(@"^\s*(?<lbl>[A-Za-z0-9_]{4,})", RegexOptions.Multiline); // Use a regex to obtain all 4 letter words in string
MatchCollection matches = lbls.Matches(text); // text is my string

foreach (Match m in matches)
{
  string mm = m.Groups["lbl"].Value; // Matches are stored in this group.
  if (!Regex.IsMatch(text, @"^\s*\b" + mm + @":\b", RegexOptions.Multiline))
  {
    text = Regex.Replace(text, @"\b" + mm + @"\b", mm + ":", RegexOptions.Multiline);
  }
}

Suppose the string is "TEST". That means the output should be "TEST:" which it is. However if code is run once more, the text should remain "TEST:" but it does not and it is "TEST::" instead. Colons keep being added. Why is this? My if statement looks fully correct.

fge · Accepted Answer · 2011-12-23 18:43:33Z

2

Try and replace ^([A-Za-z0-9_]{4})(?!:) with $1:, where $1 is the first group.

answered Dec 23, 2011 at 18:43

fge

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2 Comments

dnclem Over a year ago

? Not quite sure what you mean.

fge Over a year ago

The regex matches 4 alphanumeric characters from the beginning of input, captures them, and checks that they are not followed by a column.

Steve Dignan · Accepted Answer · 2011-12-23 19:08:53Z

1

The first time you run your code, you're searching for the value "TEST" in your input (which is simply "TEST") and replacing it with "TEST" and appending a colon to the end.

So after the first iteration, the result will be "TEST:".

The second time you run your code, you're searching for the value "TEST" in your input (which is now "TEST:") and replacing it with "TEST" and appending a colon to the end.

So after the second iteration, the result will be "TEST::".

Seems like you only want to append a colon to the end only when no colon exists(maybe?).

Try changing you "if" line to this...

if ( !Regex.IsMatch( text , @"\b" + mm + @"\b:" , RegexOptions.Multiline ) )

edited Dec 23, 2011 at 19:08

answered Dec 23, 2011 at 18:53

Steve Dignan

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3 Comments

dnclem Over a year ago

Yes, but I'm confused. Where is the problem? Also, am I not searching for the value "TEST:" in the first iteration, not "TEST"? There's a colon in the search too.

Steve Dignan Over a year ago

I just updated my answer to address your comment. I believe moving the colon in your IF statement should get you what you need... I hope.

dnclem Over a year ago

Yeah, that fixed it and I see the problem now. I placed the : INSIDE the word boundary instead of outside, silly mistake. Thanks for pointing that out.

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