Use C# to extract and replace href attribute value

Question

I am having following set of image map tags;

<map name="planetmap">
  <area shape="rect" coords="0,0,82,126" href="sun.htm" alt="Sun">
  <area shape="circle" coords="90,58,3" href="mercur.htm" alt="Mercury">
  <area shape="circle" coords="124,58,8" href="venus.htm" alt="Venus">
</map>

I need to extract href attribute and replace it with another url

I am using following code but does not seems to work;

string input = @"<area shape=""rect"" href=""http://www.google.com"">";
            string pattern = "(href=([^ ]+))";
Regex rgx = new Regex(pattern);
string result2 = rgx.Replace(input, m => m.Groups[1].Value.Replace(result,"test.com"));

Could someone please help me.

Thanks

Please delineate exactly what you mean by "it doesn't work", it will be helpful to those answering the question. — jonsca, Oct 09 '12 at 03:17
[You should not use regular expressions to parse HTML](http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags) — Guillaume, Oct 09 '12 at 03:18

score 0 · Accepted Answer · answered Oct 09 '12 at 03:21

I can see two things that may be causing an issue. The first is, your regex is checking for a string in the format of href=http://example.com. Note, there are no quotes around the URL. So, we'll need to update the regex to handle the double-quotes like your input contains.

The second is that you're using the matched group 1, but your regex is actually matching two separate groups (and you want to replace the second one). You don't need the first matching group at all, so we can actually drop this part.

In all, try updating your regex to:

href="([^"]+)"

In your variable, it will look like:

string pattern = @"href=""([^""]+)""";

Thanks I used your solution to improve mine – user778930 Oct 09 '12 at 05:17 — user778930, Oct 09 '12 at 05:17

score 0 · Answer 2 · answered Oct 09 '12 at 03:38

0

Have a look in this example:

StreamReader reader = new StreamReader("D:\\stack.html");
string testString = reader.ReadToEnd();

string replacedString = Regex.Replace(testString, @"(?<=href=).+?(?=\s)", "\"test.com\"");

StreamWriter writer = new StreamWriter("D:\\stack1.html");
writer.WriteLine(replacedString);

writer.Close();
reader.Close();

Hope you got it.

answered Oct 09 '12 at 03:38

jomsk1e

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Hay It works if you have only one href. if you have multiple it will not.. I am new to regex and often confuses me. – user778930 Oct 09 '12 at 05:05
No, it will replace all href. – jomsk1e Oct 09 '12 at 05:41

Use C# to extract and replace href attribute value

2 Answers2