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Aakash Panchal 2020-03-08 15:13:07 +05:30 committed by GitHub
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Akash Articles/RegEx/lazy_matching.html
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<html>
<head>
<style type="text/css">
@ -32,6 +33,22 @@
pre, code {
padding: 1em;
}
table {
border:1px solid black;
border-collapse: collapse;
min-width:60%;
}
th, td{
border:1px solid black;
border-collapse: collapse;
text-align: center;
}
tr:nth-child(even) {background-color: #f2f2f2;}
</style>
<script>
document.addEventListener('readystatechange', event => {
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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/4vtqc" class="embed"></iframe>
</div>
<p>To make it lazy, we use <code>?</code> quantifier, which turns the regex engine to match as less characters as possible which satisfies the regex.</p>
<p>To make it lazy, we use <code>?</code> quantifier, which turns the regex engine to match as less characters as possible which satisfies the expression.</p>
<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/4vtqf" class="embed"></iframe>
</div>
<p>Below is a table showing lazy version of all quantifiers:</p>
<table>
<tr>
<td>Quantifier</td>
<td>Lazy version</td>
</tr>
<tr>
<td>{n,m}</td>
<td>{n,m}?</td>
</tr>
<tr>
<td>{n,}</td>
<td>{n,}?</td>
</tr>
<tr>
<td>+</td>
<td>+?</td>
</tr>
<tr>
<td>*</td>
<td>*?</td>
</tr>
<tr>
<td>?</td>
<td>??</td>
</tr>
</table>
<p>So, now we can match html tags as below:</p>
<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/4vtqr" class="embed"></iframe>
</div>
<p>Let's have one more example,</p>
<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/4vthc" class="embed"></iframe>
</div>
<p><strong>Problem</strong></p>
<ol>
<li>
<p>Find an expression to match <code>href="url"</code> in html file. Note that url can be anything, like <code>https://xyz.com</code>, <code>http://abc.io/app</code>, <code>https://cde.org</code>.</p>
<p>Answer: <code>href=".*?"</code></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/4vu96" class="embed"></iframe>
</div>
</li>
<li>
What will be the match for expression <code>\w+? \w+?</code> in <code>abc cde, 123 456</code>.
<br>Answer: <code>123 4</code> and <code>abc d</code>
<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/4vuek" class="embed"></iframe>
</div>
</li>
<p>We will see how to extract things(like, urls) from the text using regex, in the "group and capturing" concept.</p>