<?php
 
$html = <<<DATA
<form>
<input type="hidden" name="test[]" />
<input type="hidden" name="old[]" />
<input type="hidden" name="new[]" />
</form>
DATA;
 
$dom = new DOMDocument('1.0', 'UTF-8');
$dom->loadHTML($html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
 
$xpath = new DOMXPath($dom);
$inputs = $xpath->query('//input[@name]');
 
foreach($inputs as $input) { 
	$name = $input->getAttribute('name');
	if (substr($name, -2) === "[]") {
		$newval = substr($name, 0, $input->getAttribute('name')->length - 2);
		$input->setAttribute('name', $newval);
	}
}
 
echo $dom->saveHTML();
 

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