在C＃中使用正则表达式突出显示html中的单词

Question

I found this article on stackoverflow

highlight words in html using regex & javascript - almost there

Using the article above, I am trying to highlight HTML text on the server using c#. The code is shown below:

string replacePattern = "$1<span style=\"background-color:yellow\">$2</span>";
string searchPattern = String.Format("(?<=^|>)(.*?)({0})(?=.*?<|$)", searchString.Trim());
content = Regex.Replace(content, searchPattern, replacePattern, RegexOptions.IgnoreCase);

The code seems to work great except when trying to highlight a word that is contained in an image source:

Search Keyword:

ABC

Search Text:

<div><img src="/site/folder/ABC.PNG" /><br />ABC</div>

The result will highlight both the text and the image name.

Any help would be greatly appreciated.

Answer 1

I'll offer up a solution, but I agree that solely using Regex for parsing HTML can eventually not be worth the effort. That said, you know more about your problem space than the rest of us, so if the HTML you're highlighting is under your control you may be able to test enough of your domain to achieve what you want with regexes.

My solution changes the regex you've supplied to take this approach:

1. Match and capture into $1 the > char, non-greedy capture chars not in set [<>]
2. Match and capture your keyword into $2
3. Match and capture into $3 non-greedy chars not in set [<>], plus the < char

Caveats:

1. well-formed HTML works best, if this html is User-Generated content (UGC), then, good luck you should've used an HTML parser :)
2. this would highlight content within <textarea>...</textarea>
3. this would highlight content within <script>...</script>

Note you could expand the capture on the lefthand side to capture the tag name and conditionally not replace for a set of tags like textarea and script.

string searchString = "ABC";
string content = "<div><img src='/site/folder/ABC.PNG' /><br />ABC</div>";
string replacePattern = "$1<span style=\"background-color:yellow\">$2</span>$3";
string searchPattern = String.Format("(>[^<>]*?)({0})([^<>]*?<)", searchString.Trim());
content = Regex.Replace(content, searchPattern, replacePattern, RegexOptions.IgnoreCase);
Console.WriteLine(content);