正则表达式＃从<a>标签中</a>提取url

Question

I am trying to extract URL from an tag, however, instead of getting https://website.com/-id1 , I am getting tag link text. Here is my code:

string text="<a style=\"font - weight: bold; \" href=\"https://website.com/-id1\">MyLink</a>";

 string parsed = Regex.Replace(text, " <[^>] + href =\"([^\"]+)\"[^>]*>", "$1 " );

    parsed = Regex.Replace(parsed, "<[^>]+>", "");

    Console.WriteLine(parsed);

The result I got was MyLink which is not what I want. I want something like

https://website.com/-id1

Any help or a link will be highly appreciated.

Answer 1

Regular expressions can be used in very specific, simple cases with HTML. For example, if the text contains only a single tag, you can use "href\\\\s*=\\\\s*\\"(?<url>.*?)\\"" to extract the URL, eg:

var url=Regex.Match(text,"href\\s*=\\s*\"(?<url>.*?)\"").Groups["url"].Value;

This pattern will return :

https://website.com/-id1

This regex doesn't do anything fancy. It looks for href= with possible whitespace and then captures anything between the first double quote and the next in a non-greedy manner ( .*? ). This is captured in the named group url .

Anything more fancy and things get very complex. For example, supporting both single and double quotes would require special handling to avoid starting on a single and ending on a double quote. The string could multiple <a> tags that used both types of quotes.

For complex parsing it would be better to use a library like AngleSharp or HtmlAgilityPack

Answer 2

Try this:

var input = "<a style=\"font - weight: bold; \" href=\"https://website.com/-id1\">MyLink</a><a style=\"font - weight: bold; \" href=\"https://website.com/-id2\">MyLink2</a>";
var r = new Regex("<a.*?href=\"(.*?)\".*?>");
var output = r.Matches(input);
var urls = new List<string>();
foreach (var item in output) {
    urls.Add((item as Match).Groups[1].Value);
}

It will find all a tags and extract their href values then store it in urls List.

Explanation

<a match begining of <a> tag
.*?href= match anything until href=
"(.*?)" match and capture anything inside ""
.*?> match end of <a> tag