{"id":1574,"date":"2019-04-19T01:00:00","date_gmt":"2019-04-18T23:00:00","guid":{"rendered":"https:\/\/demo.sidekick.be\/itenium\/regex-in-dotnet\/"},"modified":"2025-11-28T13:31:44","modified_gmt":"2025-11-28T12:31:44","slug":"regex-in-dotnet","status":"publish","type":"post","link":"https:\/\/demo.sidekick.be\/itenium\/blog\/dotnet\/regex-in-dotnet\/","title":{"rendered":".NET Regex Tutorial"},"content":{"rendered":"<p>When executing the same regex many times, prefer the static methods on <code>Regex<\/code> over <code>new Regex()<\/code> as they keep an internal cache for performance.<\/p>\n<p>Its methods may throw a <a href=\"https:\/\/docs.microsoft.com\/en-us\/dotnet\/api\/system.text.regularexpressions.regexmatchtimeoutexception?\"><code>RegexMatchTimeoutException<\/code><\/a><\/p>\n<h1 id=\"creation\">Creation<\/h1>\n<pre><code class=\"language-csharp\">var regex = new Regex(@\"d+\", RegexOptions.None);\n\nvar commentedRegex = new Regex(@\"\n    d    # Any digit\n    [0-9] # With character class\n    \", RegexOptions.IgnorePatternWhitespace);\n<\/code><\/pre>\n<ul>\n<li><code>RegexOptions.Compiled<\/code>: Increased startup time for decreased execution time.<\/li>\n<li><code>RegexOptions.IgnoreCase<\/code>.<\/li>\n<li><code>RegexOptions.ExplicitCapture<\/code>: Only explicitly named\/numbered groups are captured. (Skip the <code>(?:\u2026)<\/code>).<\/li>\n<li><code>RegexOptions.Multiline<\/code>: <code>^<\/code> and <code>$<\/code> match beginning and end of line.<\/li>\n<li><code>RegexOptions.Singleline<\/code>: <code>.<\/code> matches <code>n<\/code>.<\/li>\n<\/ul>\n<h1 id=\"tes-a-match\">Tes A Match<\/h1>\n<pre><code class=\"language-csharp\">Match match = Regex.Match(\"1-22-333\", @\"(d+)-(d+)-(d+)(-d+)?\");\n\nIReadOnlyList&lt;Group&gt; groups = match.Groups;\nAssert.Equal(5, groups.Count);\n\nAssert.Equal(\"1-22-333\", groups.First().Value);\n\nGroup one = match.Groups.Skip(1).First();\nAssert.Equal(\"1\", one.Value);\n\nGroup fours = match.Groups.Last();\nAssert.False(fours.Success);\n<\/code><\/pre>\n<h2 id=\"multiple-named-matches\">Multiple Named Matches<\/h2>\n<pre><code class=\"language-csharp\">string pattern = @\"(?&lt;one&gt;d+)-(?&lt;two&gt;d+)\";\nIReadOnlyList&lt;Match&gt; matches = Regex.Matches(\"1-22, 1-2\", pattern);\n\nAssert.Equal(2, matches.Count);\n\nMatch first = matches.First();\nAssert.Equal(\"1-22\", first.Value);\n\nMatch second = matches.Last();\nAssert.Equal(\"1-2\", second.Value);\n\n\nIReadOnlyList&lt;Group&gt; groups = first.Groups;\nGroup one = groups.Skip(1).First();\nAssert.Equal(\"one\", one.Name);\nAssert.Equal(\"1\", one.Value);\n<\/code><\/pre>\n<h1 id=\"replace\">Replace<\/h1>\n<h4 id=\"basic-usage\">Basic Usage<\/h4>\n<pre><code class=\"language-c#\">var regex = new Regex(@\"(d)-(d+)\");\nvar result = regex.Replace(\"1-22\", \"$1+$2\");\nAssert.Equal(\"1+22\", result);\n\nresult = Regex.Replace(\"1\", @\"(?&lt;amount&gt;d+)\", \"$$ ${amount}\");\nAssert.Equal(\"$ 1\", result);\n<\/code><\/pre>\n<h4 id=\"replace-with-function\">Replace with Function<\/h4>\n<pre><code class=\"language-c#\">string input = \"Hello World!\";\nstring pattern = @\"Hello\";\n\nvar result = Regex.Replace(input, pattern, (Match m) =&gt; $\"&lt;b&gt;{m.Value}&lt;\/b&gt;\");\nAssert.Equal(\"&lt;b&gt;Hello&lt;\/b&gt; World!\", result);\n<\/code><\/pre>\n<h4 id=\"other-substitutions\">Other Substitutions<\/h4>\n<ul>\n<li><code>$&amp;<\/code> : entire match<\/li>\n<li><code>$<\/code>` : before<\/li>\n<li><code>$'<\/code> : after<\/li>\n<li><code>$+<\/code> : last captured group<\/li>\n<li><code>$_<\/code> : entire input string<\/li>\n<\/ul>\n<h1>Also in this series<\/h1>\n<ul>\n<li>Part 1: <a href=\"\/javascript\/regex-in-javascript\/\">JavaScript RegExp Tutorial<\/a><\/li>\n<li>This Part: .NET Regex Tutorial<\/li>\n<li>Part 3: <a href=\"\/productivity\/regex-introduction\/\">Regular Expressions: Introduction<\/a><\/li>\n<li>Part 4: <a href=\"\/productivity\/regex-tutorial\/\">Regular Expressions: Tutorial<\/a><\/li>\n<\/ul>\n<h1>Extras<\/h1>\n<p><b>Other interesting reads<\/b><\/p>\n<ul>\n<li><a href=\"http:\/\/blog.stevenlevithan.com\/archives\/balancing-groups\">Steven Levithan: Fun with .NET Regex Balancing Groups<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Not nearly as confusing as it is in JavaScript.<\/p>\n<pre><code class=\"language-c#\">using System.Text.RegularExpressions;\n\nbool mach = Regex.IsMatch(\"input\", @\"w+\", RegexOptions.None);\nMatch match = Regex.Match(\"input\", @\"w+\");\nIReadOnlyList&lt;Match&gt; matches = Regex.Matches(\"input\", @\"w+\");\nstring result = Regex.Replace(\"input\", @\"(w+)\", \"$1\");\n<\/code><\/pre>\n","protected":false},"author":1,"featured_media":2072,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[11],"tags":[13,34],"class_list":["post-1574","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dotnet","tag-cheat-sheet","tag-regex"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>.NET Regex Tutorial - Itenium<\/title>\n<meta name=\"robots\" content=\"noindex, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\".NET Regex Tutorial - Itenium\" \/>\n<meta property=\"og:description\" content=\"Not nearly as confusing as it is in JavaScript. using System.Text.RegularExpressions; 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