Software Development by Riley

Regular Expression (RegEx)

A regular expression (shortened as regex or regexp;[1] also referred to as rational expression[2][3]) is a sequence of characters that specifies a search pattern. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation. It is a technique developed in theoretical computer science and formal language theory.

How To Replace Link Target using Regular Expression

private string ReplaceBlankTarget(string text)
{
    string pattern = @"<a href=""https:\/\/(?<link>[^""]+)"" target=""_blank"">";
    string substitution = @"<a href=""https:\/\/${link}"" target=""_self"">";

    RegexOptions options = RegexOptions.Multiline;

    Regex regex = new Regex(pattern, options);
    return regex.Replace(text, substitution);
}

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Regular Expression Tools

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RegEx to extract link (a) with href only

string pattern = @"(<a.*?(?<href>href=\x22.*?\x22).*?>)";
string substitution = "<a ${href}>";
RegexOptions options = RegexOptions.Multiline;

Regex regex = new Regex(pattern, options);
string result = regex.Replace(input, substitution);

Additional information for Substitutions in Regular Expressions

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How to Select Script Tag in HTML using RegEx

Regular expression to select script tag:

(<script[\s\S]*?>[\s\S]*?<\/script>)

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How to get href URL from HTML anchor tags using RegEx

This will capture the URL as well as the text.

string input = @"<a href=""\page1.htm"">Page 1</a><a href=""\page2.htm"">Page 2</a>";
				
var matches = Regex.Matches(input, @"<a\shref=""(?<url>.*?)"">(?<text>.*?)</a>");

foreach (Match m in matches)
{
	Console.WriteLine("URL: " + m.Groups["url"].Value + "; Text: " + m.Groups["text"].Value);
}

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How to Match Semantic Version Numbers with Regex

When working with software versions like 1.0.2 or 3.45.12-SNAPSHOT, it's common to use regular expressions (regex) to validate or extract these patterns. This Snipp shows you a simple and effective way to match such version numbers using regex.