How to replace all match with another format using Regex

June 7, 2023

Here I have html contains hrefs as follows:

<a href="https://www.test.com/help">a</a><br/>
...
other html text
...
<a href="https://www.test.com/help2">b</a><br/>
...
other html text
...
<a href="https://www.test.com/help3">c</a>

How to use Regex to replace all . character to space character in href?

<a href="https://www test com/help">a</a><br/>
<a href="https://www test com/help2">b</a><br/>
<a href="https://www test com/help3">c</a>

I am trying the follwing, but not work:

string textToHandle = "html text here";
string newUrl = string.Empty;
Regex rg = new Regex("(?<=(href=\"))[.\\s\\S]*?(?=(\"))", RegexOptions.IgnoreCase);

MatchCollection collection = rg.Matches(textToHandle);
foreach (Match match in collection)
{
    string u = match.Groups[0].Value;
    newUrl = rg.Replace(textToHandle, u.Replace(".", " "));
    Console.WriteLine(newUrl);
}

Console.WriteLine(newUrl);

>Solution :

In order to replace all . characters with spaces within the href attribute, you can modify your regex pattern to (?<=href="")[^""]*(?="") and use the Regex.Replace() method with a MatchEvaluator:

string textToHandle = "<a href=\"https://www.test.com/help3\">c</a>";
string newUrl = string.Empty;

// Updated regex pattern to match href values
string pattern = @"(?<=href="")[^""]*(?="")";
Regex rg = new Regex(pattern, RegexOptions.IgnoreCase);

// Match evaluator to replace '.' with ' '
MatchEvaluator evaluator = match => match.Value.Replace(".", " ");

// Replace all occurrences in the input text
newUrl = rg.Replace(textToHandle, evaluator);

Console.WriteLine(newUrl);
Console.ReadKey();

Regex Explaination

(?<=href="") Positive lookbehind to ensure the match is preceded by href=".
[^""]* Match any character except " (double quotes), zero or more times.
(?="") Positive lookahead to ensure the match is followed by a double quote ".