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Akash Articles/RegEx/Quantifier.html
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<html>
<head>
<style type="text/css">
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<h2 id="quantifiersrepetition">Quantifiers (Repetition)</h2>
<h2 id="quantifiersrepetition">Quantifiers (Repetition)</h2>
<p>To match 3 digit patterns, we can use <code>[0-9][0-9][0-9]</code>. What if we have n digit patterns? We have to write <code>[0-9]</code> n times, but that is a waste of time. Here is when quantifiers come for help.</p>
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<div class="container">
<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vtp2" class="embed"></iframe>
</div></li>
</ol>
</div>
<p><strong>Note:</strong> If you don't write the upper bound(<code>{min,}</code>), then it basically means, there is no limit for maximum repetitions.</p>
</li>
<ol>
<li><p><strong><code>+</code> quantifier:</strong> It is equivalent to <code>{1,}</code>-at least one occurrence.</p>
<div class="container">
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<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vtpb" class="embed"></iframe>
</div>
<ol>
<li><strong><code>?</code> quantifier:</strong> It is equivalent to <code>{0,1}</code>, either zero or one occurrence. <code>?</code> is very useful for optional occurrences in patterns.</li></ol>
<li><strong><code>?</code> quantifier:</strong> It is equivalent to <code>{0,1}</code>, either zero or one occurrence. <code>?</code> is very useful for optional occurrences in patterns.</li>
<p>Let's see an example to match negative and positive numbers.</p>
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<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vtpk" class="embed"></iframe>
</div></li>
<li><p>Predict the output of the following regex:
<li><p>Predict the output of the following regex:<br>
<strong>RegEx</strong>: <code>[abc]{2,}</code> <br>
<strong>Text</strong>:
<code>aaa
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<h3 id="natureofquantifiers">Nature of Quantifiers</h3>
<p>HTML tag is represented as <tag_name>some text</tag_name>. For example, <code>&lt;title&gt;Regular expression&lt;/title&gt;</code></p>
<p>HTML tag is represented as <code>&lt;tag_name>some text&lt;/tag_name></code>. For example, <code>&lt;title&gt;Regular expression&lt;/title&gt;</code></p>
<p>So, can you figure out an expression that will match both <tag_name> &amp; </tag_name>?</p>
<p>So, can you figure out an expression that will match both <code>&lt;tag_name></code> &amp; <code>&lt;/tag_name></code>?</p>
<p>Most of the people will say, it is <code>&lt;.*&gt;</code>. But it gives different result.</p>
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<p>To solve this issue, we use <code>?</code> quantifier and it is called <strong>lazy matching</strong>. We will discuss it next.</p>
<p>Predict the output of the following regex:
<p>Predict the output of the following regex: <br>
<strong>RegEx</strong>: <code>(var|let)\s[a-zA-Z0-9_]\w* =\s"?\w+"?;</code> <br>
<strong>Text</strong>:
<code>var carname = "volvo";