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Akash Articles/RegEx/boundary_matchers.html
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<html>
<head>
<style type="text/css">
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<li><p>There is a slight change in javascript code, we were using up till now. Instead of <code>/____/g</code>, we will now use <code>/____/gm</code>. Modifier 'm' is used to perform multiline search. Notice it in next images!</p></li>
<li><p>Word character can be represented by, <code>[A-Za-z0-9_]</code>.</p></li>
</ul>
<ol>
<li><p><strong>Anchor <code>^</code></strong>: It is used to match patterns at the very start of a line.
For 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/4vtsb" class="embed"></iframe>
</div></li>
</ul>
<p>It will show a match, only if the pattern is occuring at the start of the line.</p>
<ul>
<li><p><strong>Anchor <code>$</code></strong>: Similarly, <code>$</code> is used to match patterns at the very end of a line.</p>
<p><div class="container"></p></li>
</ul>
<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/4vtsb" class="embed"></iframe>
<p></div></p>
</div>
<p>It will show a match, only if the pattern is occuring at the end of a line.</p>
<p>Example, both <code>^</code> and <code>$</code>,
<div class="container"></p>
<p>Example, both <code>^</code> and <code>$</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/4vtsb" class="embed"></iframe>
</div>
<p></div></p>
<ul>
<li><p><strong>Anchors <code>\b</code> &amp; <code>\B</code></strong>: <code>\b</code> is called <strong>word boundary character</strong>. </p>
<p>Below is a list of positions, which qualifies as a <strong>boundary</strong> for <code>\b</code>:
If Regex-pattern is ending(or starting) with,</p>
<ul>
<li>A word character, then boundary is itself(word character). Let's call it a word boundary.</li>
<li>A word character, then boundary is itself(word character). Let's call it a <strong>word boundary</strong>.</li>
<li>A non-word character, then boundary is the next word-character. Let's call it a non-word boundary.</li></ul>
<p>So, in short <code>\b</code> is only looking for word-character at boundaries, so it is called <strong>word boundary character</strong>.</p>
<li>A non-word character, then boundary is the next word-character. Let's call it a <strong>non-word boundary</strong>.</li></ul>
<p>So, in short <code>\b</code> is only looking for word-character at boundaries, so it is called "word boundary character"</strong>.</p>
<p>Let's first observe some examples to understand it's working:</p></li>
</ul>
<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/4vu99" class="embed"></iframe>
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<p>Now, let's look at one more example.</p>
<pre><code>&amp;lt;div class="container"&amp;gt;
</code></pre>
<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/4vu9c" class="embed"></iframe>
<p></div></p>
</div>
<p>Here <code>\+</code> will show a match for <code>+</code>, check it out in appendix.</p>
<p>What did you observe?
<p>What did you observe? <br>
<strong>First observation:</strong> Our pattern is starting with a non-word character and ending with a word character. So, the match occurs only if there is a substring having a non-word boundary at starting and word boundary at the ending.</p>
<p><strong>Second observation:</strong> Non-word character after a word-boundary does not affect the result. </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/4vu9u" class="embed"></iframe>
</div>
</ol>
<p><strong>Note:</strong> <code>\A</code> and <code>\z &amp; \Z</code> are another anchors, which are used to match at the very start of input text and at very end of input text respectively. But it is not supported in Javascript.</p>
<p>Predict the output of the following regex:</p>
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gadfaJ%33
Abjapda454&1 spc
bjaphgu12$
</code>
Answer: </li>
</ol>
</code><br>
Answer:
<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/4vua4" class="embed"></iframe>
</div>
</li>
<ol>
<li><strong>RegEx:</strong> <code>\b\w+:\B</code> <br>
<strong>Text:</strong> <code>1232: , +1232:, abc:, abc:a, abc89, (+abc::)</code>
Answer: </li>
</ol>
<strong>Text:</strong> <code>1232: , +1232:, abc:, abc:a, abc89, (+abc::)</code><br>
Answer:
<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/4vua7" class="embed"></iframe>
</div>
</li>
</ol>
<script type="text/javascript">
document.addEventListener('DOMContentLoaded', (event) => {