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copied!<p>The notion that regex doesn't support inverse matching is not entirely true. You can mimic this behavior by using negative look-arounds:</p> <pre><code>^((?!hede).)*$ </code></pre> <p>The regex above will match any string, or line without a line break, <strong>not</strong> containing the (sub)string 'hede'. As mentioned, this is not something regex is "good" at (or should do), but still, it <em>is</em> possible. </p> <p>And if you need to match line break chars as well, use the <a href="http://perldoc.perl.org/perlre.html#Modifiers" rel="noreferrer">DOT-ALL modifier</a> (the trailing <code>s</code> in the following pattern):</p> <pre><code>/^((?!hede).)*$/s </code></pre> <p>or use it inline:</p> <pre><code>/(?s)^((?!hede).)*$/ </code></pre> <p><em>(where the <code>/.../</code> are the regex delimiters, i.e., not part of the pattern)</em></p> <p>If the DOT-ALL modifier is not available, you can mimic the same behavior with the character class <code>[\s\S]</code>:</p> <pre><code>/^((?!hede)[\s\S])*$/ </code></pre> <h2>Explanation</h2> <p>A string is just a list of <code>n</code> characters. Before, and after each character, there's an empty string. So a list of <code>n</code> characters will have <code>n+1</code> empty strings. Consider the string <code>"ABhedeCD"</code>:</p> <pre><code> ┌──┬───┬──┬───┬──┬───┬──┬───┬──┬───┬──┬───┬──┬───┬──┬───┬──┐ S = │e1│ A │e2│ B │e3│ h │e4│ e │e5│ d │e6│ e │e7│ C │e8│ D │e9│ └──┴───┴──┴───┴──┴───┴──┴───┴──┴───┴──┴───┴──┴───┴──┴───┴──┘ index 0 1 2 3 4 5 6 7 </code></pre> <p>where the <code>e</code>'s are the empty strings. The regex <code>(?!hede).</code> looks ahead to see if there's no substring <code>"hede"</code> to be seen, and if that is the case (so something else is seen), then the <code>.</code> (dot) will match any character except a line break. Look-arounds are also called <em>zero-width-assertions</em> because they don't <em>consume</em> any characters. They only assert/validate something. </p> <p>So, in my example, every empty string is first validated to see if there's no <code>"hede"</code> up ahead, before a character is consumed by the <code>.</code> (dot). The regex <code>(?!hede).</code> will do that only once, so it is wrapped in a group, and repeated zero or more times: <code>((?!hede).)*</code>. Finally, the start- and end-of-input are anchored to make sure the entire input is consumed: <code>^((?!hede).)*$</code></p> <p>As you can see, the input <code>"ABhedeCD"</code> will fail because on <code>e3</code>, the regex <code>(?!hede)</code> fails (there <em>is</em> <code>"hede"</code> up ahead!).</p>

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