Practical Regex 1: Using Named Capturing Groups

Still using numbered group of capture value in Regex? You may forget, or the index changed if the requirement changed. For example, you want to get a csrf value from a form field with the following regex example:

name="csrf" value="(.{32})"

For input field csrf with 32 chars value “4X0ZfDKr71KHCec7SOkoJ5onq1PTCN3v”, you want to get the value, you will need to get index 1 for it with PHP:

<?php

$pattern = '#name="csrf" value="(.{32})"#';
$content = <<<'HTML_CONTENT'
<form>
    <input type="hidden" name="csrf" value="4X0ZfDKr71KHCec7SOkoJ5onq1PTCN3v" />
    <input type="submit" />
</form>
HTML_CONTENT;

preg_match($pattern, $content, $matches);
if ($matches !== []) {
    echo $matches[1];
}

To handle the possible forgotten index or changed index that can create a bug, you can use named capturing groups, so you can change to:

name="csrf" value="(?<csrf_value>.{32})"

Now, you can get it easily:

<?php

$pattern = '#name="csrf" value="(?<csrf_value>.{32})"#';
$content = <<<'HTML_CONTENT'
<form>
    <input type="hidden" name="csrf" value="4X0ZfDKr71KHCec7SOkoJ5onq1PTCN3v" />
    <input type="submit" />
</form>
HTML_CONTENT;

preg_match($pattern, $content, $matches);
if ($matches !== []) {
    echo $matches['csrf_value'];
}

That’s it 😉

Ref: https://www.regular-expressions.info/named.html