htmlspecialchars only on code tags

htmlspecialchars-only-code-tags.php

<?php
// htmlspecialchars only on <code></code> tags.

// test data
$textToScan = "Hi <code>test12</code><br>
    Line 2 <code><br>
    Test <b>Bold</b><br></code><br>
    ";

// the regex pattern (case insensitive & multiline
$search = "~<code>(.*?)</code>~is";

// first look for all CODE tags and their content
preg_match_all($search, $textToScan, $matches);

// now replace all the CODE tags and their content with a htmlspecialchars() content
foreach($matches[1] as $match){
    $replace = htmlspecialchars($match);
    // now replace the previously found CODE block
    $textToScan = str_replace($match, $replace, $textToScan);
}

// output result
echo $textToScan;