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Search for a url in a string and remove enclosing tag

I have a string in which I need to search for a url and get its immediate enclosing script tag and remove it.
example
string test="<script>test</script><script
src="https://cdn.getsmartcontent.com/xxxxx.js"></script><script></script>"
should give
string test="<script>test</script><script></script>"
The xxxxx.js can be any alphanumeric name

The correct answer is use the HTML Agility Pack and parse the html properly
However, in regards to you comment
I have 13000 sharepoint sites and for each site I have to parse the
master page and remove the above specific script tag
You can use something nasty like this i guess :/
Regex.Replace(yourPage, #"<script src=""https://cdn.getsmartcontent.com/.+?\/script>", String.Empty);
You could use the multiline option i guess, but this is still a bad idea
Note/Disclaimer/Warning : See bold comment

HTML Decode and Encode

I have tried to decode the html text that i have in the databse in my MVC 3 Razor application.
the html text in the databse is not encoded.
I tries httpUtility.decode , server.decode but none of them work.
finally i managed to make it work with Html.raw(string)
sample of non working code
#Server.HtmlDecode(item.ShortDescription)
#HttpUtility.HtmlDecode(item.ShortDescription)
Do you know why we can not use html.decode in my case !
I thought this would save some one else from looking for few hours.

It works just fine to decode the text, but then it will automatically be encoded again when it's put in the page using the # syntax.
The Html.Raw method wraps the string in an HtmlString, which tells the razor engine not to encode it when it's put in the page.

If you want to display the value as-is without any HTML encoding you could use the Html.Raw helper:
#Html.Raw(item.ShortDescription)
Be warned thought that by doing this you are opening your site to XSS attacks so you should be very careful about what HTML this ShortDescription property contains. If it is the user that enters it you should absolutely ensure that it is safe. You could use the AntiXss library for this.
Do you know why we can not use html.decode in my case !
Because Html.Decode returns a string and when you feed a string to the #() Razor function it automatically Html encodes it again and ruins your previous efforts. That's why the Html.Raw helper exists.

Best way to escape javascript string? (json?)

Using C# .net I am parsing some data with some partial html/javascript inside it (i dont know who made that decision) and i need to pull a link. The link looks like this
http:\/\/fc0.site.net\/fs50\/i\/2009\/name.jpg
It came from this which i assume is javascript and looks like json
"name":{"id":"589","src":"http:\/\/fc0.site.net\/fs50\/i\/2009\/name.jpg"}
But anyways how should i escape the first link so i get
http://fc0.site.net/fs50/i/2009/name.jpg
In this case i could just replace '\' with '' since links dont contain \ nor " so i could do that but i am a fan of knowing the right solution and doing things properly. So how might i escape this. After looking at that link for a minute i thought is that valid? does java script or json escape / with \? It doesnt seem like it should?

In your case:
"name":{"id":"589","src":"http://fc0.site.net/fs50/i/2009/name.jpg"}
"/" is a valid escape sequence. However, it is not required that / be escaped. You may escape it if you need to. The reason JSON explicitly allows escaping of slash is because HTML does not allow a string in a to contain "...
Update:
Check out this post

Odd, it doesn’t look like any JavaScript/JSON escaping you’d expect. You can have forward slashes in JavaScript strings just fine.

Why dont you try a regex on the escaped slashes to replace them in the C# code...
String url = #"http:\/\/fc0.site.net\/fs50\/i\/2009\/name.jpg";
String pattern = #"\\/";
String cleanUrl = Regex.Replace(url, pattern, "/");
Hope it helps!

Actually you want to unescape the string. Answered in this question.

How can I deal with ampersands in a mail client's mailto links?

I have an ASP.NET/C# application, part of which converts WWW links to mailto links in an HTML email.
For example, if I have a link such as:
www.site.com
It gets rewritten as:
mailto:my#address.com?Subject=www.site.com
This works extremely well, until I run into URLs with ampersands, which then causes the subject to be truncated.
For example the link:
www.site.com?val1=a&val2=b
Shows up as:
mailto:my#address.com?Subject=www.site.com?val1=a&val2=b
Which is exactly what I want, but then when clicked, it creates a message with:
subject=www.site.com?val1=a
Which has dropped the &val2, which makes sense as & is the delimiter in a mailto command.
So, I have tried various other was to work around this with no success.
I have tried implicitly quoting the subject='' part and that did nothing.
I (in C#) replace '&' with & which Live Mail and Thunderbird just turn back into:
www.site.com?val1=a&val2=b
I replaced '&' with '%26' which resulted in:
mailto:my#address.com?Subject=www.site.com?val1=a%26amp;val2=b
In the mail with the subject:
www.site.com?val1=a&val2=b
EDIT:
In response to how URL is being built, this is much trimmed down but is the gist of it. In place of the att.Value.Replace I have tried System.Web.HtmlUtility.URLEncode calls which also results in a failure
HtmlAgilityPack.HtmlNodeCollection nodes =doc.DocumentNode.SelectNodes("//a[#href]");
foreach (HtmlAgilityPack.HtmlNode link in nodes)
{
HtmlAgilityPack.HtmlAttribute att = link.Attributes["href"];
att.Value = att.Value.Replace("&", "%26");
}

Try mailto:my#address.com?Subject=www.site.com?val1=a%26val2=b
& is an HTML escape code, whereas %26 is a URL escape code. Since it's a URL, that's all you need.
EDIT: I figured that's how you were building your URL. Don't build URLs that way! You need to get the %26 in there before you let anything else parse or escape it. If you really must do it this way (which you really should try to avoid), then you should search for "&" instead of just "&" because the string has already been HTML escaped at this point.
So, ideally, you build your URL properly before it's HTML escaped. If you can't do it properly, at least search for the right string instead of the wrong one. "&" is the wrong one.

You cant put any character as subject. You could try using System.Web.HttpUtility.URLEncode function on the subject´s value...

Using the URL escape code %26 is the right way.
Sadly this is still not working on the Android OS because of bug 8023

What I ended up doing for my case was eliminating the &.
www.site.com/mytest.php?val1=a=b=c. Where the 2nd and 3rd = would be equivalent to www.site.com?val1=a&val2=b&val3=c
In mytest.php I explode on ? and then explode again on =.
A total hack I know but it does work for me.

Wikilinks - turn the text [[a]] into an internal link

I need to implement something similar to wikilinks on my site. The user is entering plain text and will enter [[asdf]] wherever there is an internal link. Only the first five examples are really applicable in the implementation I need.
Would you use regex, what expression would do this? Is there a library out there somewhere that already does this in C#?

On the pure regexp side, the expression would rather be:
\[\[([^\]\|\r\n]+?)\|([^\]\|\r\n]+?)\]\]([^\] ]\S*)
\[\[([^\]\|\r\n]+?)\]\]([^\] ]\S*)
By replacing the (.+?) suggested by David with ([^\]\|\r\n]+?), you ensure to only capture legitimate wiki links texts, without closing square brackets or newline characters.
([^\] ]\S+) at the end ensures the wiki link expression is not followed by a closing square bracket either.
I am note sure if there is C# libraries already implementing this kind of detection.
However, to make that kind of detection really full-proof with regexp, you should use the pushdown automaton present in the C# regexp engine, as illustrated here.

I don't know if there are existing libraries to do this, but if it were me I'd probably just use regexes:
match \[\[(.+?)\|(.+?)\]\](\S+) and replace with \1\3
match \[\[(.+?)\]\](\S+) and replace with \1\2
Or something like that, anyway.

Although this is an old question and already answered, I thought I'd add this as an addendum for anyone else coming along. The existing two answers do all the real work and got me 90% there, but here is the last bit for anyone looking for code to get straight on with trying:
string html = "Some text with a wiki style [[page2.html|link]]";
html = Regex.Replace(html, #"\[\[([^\]\|\r\n]+?)\|([^\]\|\r\n]+?)\]\]([^\] ]\S*)", #"$2$3");
html = Regex.Replace(html, #"\[\[([^\]\|\r\n]+?)\]\]([^\] ]\S*)", #"$1$2");
The only change to the actual regex is I think the original answer had the replacement parts the wrong way around, so the href was set to the display text and the link was shown on the page. I've therefore swapped them.