Lecture_Notes/articles/Akash Articles/rendered/RegEx/Practial_applications.html

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<h2 id="practicalapplicationsofregex">Practical Applications of RegEx</h2>
<ol>
<li>Syntax highlighting systems</li>
<li>Data scraping and wrangling</li>
<li>In find and replace facility of text editors</li>
</ol>
<p>Let's look at some classical examples of RegEx.</p>
<h2 id="numberranges">Number Ranges</h2>
<p>Can you find a regex matching all integers from 0 to 255?</p>
<p>First, Let's look at how can we match all integers from 0 to 59:</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/4vubt" class="embed"></iframe>
</div>
<p>As you can see, we have used <code>?</code> quantifier to make the first digit(0-5) optional. Now, can you solve it for 0-255?</p>
<p>Hint : Use OR operator.</p>
<p>We can divide the range 0-255 into three ranges: 0-199, 200-249 &amp; 250-255. Now, creating an expression, for each of them independently, is easy.</p>
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<table>
<tr>
<td>Range</td>
<td>RegEx</td>
</tr>
<tr>
<td>0-199</td>
<td>[01][0-9][0-9]</td>
</tr>
<tr>
<td>200-249</td>
<td>2[0-4][0-9]</td>
</tr>
<tr>
<td>250-255</td>
<td>25[0-5]</td>
</tr>
</table>
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<p>Now, by using OR operator, we can match the whole 0-255 range.</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/4vuc0" class="embed"></iframe>
</div>
<p>As you can see, the above regex is not going to match 0, but 000. So, how can you modify the regex which matches 0 as well, rather than matching 001 only?</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/4vuc3" class="embed"></iframe>
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<p>We have just used <code>?</code> quantifier.</p>
<h2 id="validateanipaddress">Validate an IP address</h2>
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<p>IP address consists of digits from 0-255 and 3 points(<code>.</code>). Valid IP address format is <br> (0-255).(0-255).(0-255).(0-255).</p>
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<p>For example, 10.10.11.4, 255.255.255.255, 234.9.64.43, 1.2.3.4 are Valid IP addresses.</p>
<p>Can you find a regex to match an IP-address?</p>
<p>We have already seen, how to match number ranges and to match a point, we use escaped-dot(<code>\.</code>). But in IP address, we don't allow leading zeroes in numbers like 001. </p>
<p>So, We have to divide the range in four sub-ranges: 0-99, 100-199, 200-249, 250-255. And finally we use OR-operator.</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/4vuc9" class="embed"></iframe>
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<p>So, Regex to match IP Address is as below:
<img src="https://lh3.googleusercontent.com/n2CaC-8Q8NH-H5RkDrCM4AQQkV2PamIAlA3dwljdRsW33WWoj18qJEIN5iyzjLzfifHj-dh-IW-u=s1600" alt="enter image description here" /></p>
<p><strong>Note:</strong> The whole expression is contiguous, for the shake of easy understanding it is shown the way it is.</p>
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