{"id":1904,"date":"2023-06-01T07:58:41","date_gmt":"2023-06-01T00:58:41","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1904"},"modified":"2023-06-01T07:58:43","modified_gmt":"2023-06-01T00:58:43","slug":"regex-anchors","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-regular-expression\/regex-anchors\/","title":{"rendered":"Regex Anchors"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn about regex anchors and how to use them to match the position at the beginning and then end of a line.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to the regex anchors<\/h2>\n\n\n\n<p>Anchors in regular expressions are special characters that define specific positions within the text for matching.<\/p>\n\n\n\n<p>Unlike the <a href=\"https:\/\/csharptutorial.net\/csharp-regular-expression\/csharp-regex-character-classes\/\">character classes<\/a>, anchors do not match any characters themselves but represent the positions in the text where a match should occur.<\/p>\n\n\n\n<p>Anchors are useful when you want to enforce constraints on where a pattern should match within the input string.<\/p>\n\n\n\n<p>Anchors have two types:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Start of line anchor (^):<\/strong> matches the position at the beginning of a line. When you place the caret (^) at the beginning of a regular expression, it ensures the pattern must appear at the start of the line.<\/li>\n\n\n\n<li><strong>End of line anchor ($):<\/strong> matches the position at the end of a line. When you place the dollar sign ($) at the end of a regular expression, it ensures the preceding pattern must appear at the end of a line.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Regex anchors examples<\/h2>\n\n\n\n<p>The following example uses the <code>\\d<\/code> character class to match two digits in a time string:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">using<\/span> System.Text.RegularExpressions;\n<span class=\"hljs-keyword\">using<\/span> <span class=\"hljs-keyword\">static<\/span> System.Console;\n\n\n<span class=\"hljs-keyword\">var<\/span> time = <span class=\"hljs-string\">\"11:30\"<\/span>;\n<span class=\"hljs-keyword\">var<\/span> pattern = <span class=\"hljs-string\">@\"\\d\\d\"<\/span>;\n\n<span class=\"hljs-keyword\">var<\/span> matches = Regex.Matches(time, pattern);\n<span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> match <span class=\"hljs-keyword\">in<\/span> matches)\n{\n    WriteLine(match);\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-number\">11<\/span>\n<span class=\"hljs-number\">30<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It returns two matches because both <code>\\d\\d<\/code> pattern matches both 11 and 30.<\/p>\n\n\n\n<p>However, if you use the <code>^<\/code> anchor character at the beginning of the regular expression pattern, it will match only 11 like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">using<\/span> System.Text.RegularExpressions;\n<span class=\"hljs-keyword\">using<\/span> <span class=\"hljs-keyword\">static<\/span> System.Console;\n\n\n<span class=\"hljs-keyword\">var<\/span> time = <span class=\"hljs-string\">\"11:30\"<\/span>;\n<span class=\"hljs-keyword\">var<\/span> pattern = <span class=\"hljs-string\">@\"^\\d\\d\"<\/span>;\n\n<span class=\"hljs-keyword\">var<\/span> matches = Regex.Matches(time, pattern);\n<span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> match <span class=\"hljs-keyword\">in<\/span> matches)\n{\n    WriteLine(match);\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-number\">11<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>^\\d\\d<\/code> ensures that the match occurs at the beginning of the input string.<\/p>\n\n\n\n<p>Similarly, when you use the <code>$<\/code> anchor at the end of the regular expression pattern, it will match only at the end of the string:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">using<\/span> System.Text.RegularExpressions;\n<span class=\"hljs-keyword\">using<\/span> <span class=\"hljs-keyword\">static<\/span> System.Console;\n\n\n<span class=\"hljs-keyword\">var<\/span> time = <span class=\"hljs-string\">\"11:30\"<\/span>;\n<span class=\"hljs-keyword\">var<\/span> pattern = <span class=\"hljs-string\">@\"\\d\\d$\"<\/span>;\n\n<span class=\"hljs-keyword\">var<\/span> matches = Regex.Matches(time, pattern);\n<span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> match <span class=\"hljs-keyword\">in<\/span> matches)\n{\n    WriteLine(match);\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-number\">30<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Regex anchors match the position, not the characters.<\/li>\n\n\n\n<li>The caret anchor (<code>^<\/code>) matches at the beginning of a line.<\/li>\n\n\n\n<li>The dollar anchor (<code>$<\/code>) matches at the end of a line.<\/li>\n<\/ul>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful ?<\/div>\n\t\t<div class=\"wth-thumbs\">\n\t\t\t<button\n\t\t\t\tdata-post=\"1904\"\n\t\t\t\tdata-post-url=\"https:\/\/www.csharptutorial.net\/csharp-regular-expression\/regex-anchors\/\"\n\t\t\t\tdata-post-title=\"Regex Anchors\"\n\t\t\t\tdata-response=\"1\"\n\t\t\t\tclass=\"wth-btn-rounded wth-yes-btn\"\n\t\t\t>\n\t\t\t\t<svg\n\t\t\t\t\txmlns=\"http:\/\/www.w3.org\/2000\/svg\"\n\t\t\t\t\tviewBox=\"0 0 24 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