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https://github.com/dholerobin/Lecture_Notes.git
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100 lines
3.3 KiB
HTML
100 lines
3.3 KiB
HTML
<html>
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<head>
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<style type="text/css">
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.container {
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position: static;
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width: 800px;
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height: 350px;
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overflow: hidden;
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}
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.embed {
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height: 100%;
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width: 100%;
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min-width: 1000px;
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margin-left: -360px;
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margin-top: -57px;
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overflow: hidden;
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}
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body {
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width: 800px;
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margin: auto;
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padding: 1em;
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font-family: "Open Sans", sans-serif;
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line-height: 150%;
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letter-spacing: 0.1pt;
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}
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img {
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width: 90%;
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text-align: center;
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margin: auto;
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box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
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}
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pre, code {
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padding: 1em;
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}
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</style>
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<script>
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document.addEventListener('readystatechange', event => {
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if (event.target.readyState === "complete")
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document.activeElement.blur();
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});
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</script>
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<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/styles/default.min.css">
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<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/highlight.min.js"></script>
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</head>
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<body>
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<h2 id="lazymatching">Lazy matching:</h2>
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<p>As we have seen, the default nature of quantifiers is greedy, so it will match as many characters as possible.</p>
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<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/4vtqc" class="embed"></iframe>
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</div>
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<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>
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<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/4vtqf" class="embed"></iframe>
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</div>
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<p>So, now we can match html tags as below:</p>
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<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/4vtqr" class="embed"></iframe>
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</div>
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<p>Let's have one more example,</p>
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<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/4vthc" class="embed"></iframe>
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</div>
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<p><strong>Problem</strong></p>
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<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>
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<p>Answer: <code>href=".*?"</code></p>
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<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/4vu96" class="embed"></iframe>
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</div>
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<p>We will see how to extract things(like, urls) from the text using regex, in the "group and capturing" concept.</p>
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<script type="text/javascript">
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document.addEventListener('DOMContentLoaded', (event) => {
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document.querySelectorAll('pre code').forEach((block) => {
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hljs.highlightBlock(block);
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});
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});
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</script>
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</body>
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</html>
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