mirror of
https://github.com/dholerobin/Lecture_Notes.git
synced 2025-03-16 22:29:57 +00:00
148 lines
4.2 KiB
HTML
148 lines
4.2 KiB
HTML
|
|
<html>
|
|
<head>
|
|
<style type="text/css">
|
|
.container {
|
|
position: static;
|
|
width: 800px;
|
|
height: 350px;
|
|
overflow: hidden;
|
|
}
|
|
.embed {
|
|
height: 100%;
|
|
width: 100%;
|
|
min-width: 1000px;
|
|
margin-left: -360px;
|
|
margin-top: -57px;
|
|
overflow: hidden;
|
|
}
|
|
body {
|
|
width: 800px;
|
|
margin: auto;
|
|
padding: 1em;
|
|
font-family: "Open Sans", sans-serif;
|
|
line-height: 150%;
|
|
letter-spacing: 0.1pt;
|
|
}
|
|
img {
|
|
width: 90%;
|
|
text-align: center;
|
|
margin: auto;
|
|
box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
|
|
}
|
|
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 => {
|
|
if (event.target.readyState === "complete")
|
|
document.activeElement.blur();
|
|
});
|
|
</script>
|
|
|
|
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/styles/default.min.css">
|
|
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/highlight.min.js"></script>
|
|
</head>
|
|
<body>
|
|
|
|
|
|
|
|
|
|
<h2 id="lazymatching">Lazy matching:</h2>
|
|
|
|
<p>As we have seen, the default nature of quantifiers is greedy, so it will match as many characters as possible.</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/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 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><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>
|
|
|
|
<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>
|
|
|
|
|
|
|
|
<script type="text/javascript">
|
|
document.addEventListener('DOMContentLoaded', (event) => {
|
|
document.querySelectorAll('pre code').forEach((block) => {
|
|
hljs.highlightBlock(block);
|
|
});
|
|
});
|
|
</script>
|
|
</body>
|
|
</html>
|