Question

Since this is my first question here on stackoverflow I hope my question is correctly asked.

Basicly I have a normal .txt file which contains any text like:

car accident
people died
cat without owner


<!-- Text added at 6/29/2011 9:20:38 AM -->

Some addintional Text
other Text added
add Text

I have a write/append function which allows the user to append some text and set a little timestamp.

So my problem is: With another function, you can search and replace text in the textfile, but as you can guess if someone wants to replace the word “Text” it will be replaced in the xml-stylish comment(timestamp) as well.

My result until now is

content = Regex.Replace(content,"[^<+.*"+input+".*>+]*", replace);
//content = content of the .txt file, input = search term, replace = string to replace

But this fails miserably, as some regex pro’s will see without executing it.

Now I hope that some regex pro could help me out here and provide me a search pattern which replaces the normal text but ignores the timestamp.

I’m not realy aware of the logic from regex until now, nevertheless I understand the single expressions so this would be a hook for me to understand Regex more properly.

Thanks in advice.

Answer 1

If I understand your question correctly, you want to replace every instance of “Text” except for the one(s) inside the comment.

The easist way is to use a negative lookbehind (fantastic description here) as below:

content = Regex.Replace(content, @"(?<!<!--.*?)" + input, replace);

What you’re doing is attempting to replace a repetition of any length of a character that is NOT <+.*> or a character contained in input with the value in replace.

If you’re going to be working a lot with Regex, I would HIGHLY recommend giving the website above a good read. It’s hands down the best intro to Regex that I’ve found, the time spent now will save you lots of headaches later!

Edit

Updated to add flexibility thanks to @stema