输入为html时，preg_replace返回null（但不是所有时间）

I am reading in html from a few different sources which I have to manipulate. As part of this I have a number of preg_replace() calls where I have to replace some of the information within the html received.

On 90% of the sites I have to do this on, everything works fine, the remaining 10% are returning NULL on each of the preg_replace() calls.

I've tried increasing the pcre.backtrack_limit and pcre.recursion_limit based on other articles I've found which appear to have the same problem, but this has been to no avail.

I have output preg_last_error() which is returning '4' for which the PHP documentation isn't proving very helpful at all, so if anyone can shed any light on this it might start to point me in the right direction, but I'm stumped.

One of the offending examples is:

$html = preg_replace('@<script[^>]*?.*?</script>@siu', '', $html);

but as I said, this works 90% of the time.

Don't parse HTML with regex. Use a real DOM parser:

$dom = new DOMDocument;
$dom->loadHTML($html);
$scripts = $dom->getElementsByTagName('script');
while ($el = $scripts->item(0)) {
    $el->parentNode->removeChild($el);
}
$html = $dom->saveHTML();

You have bad utf-8.

/**
 * Returned by preg_last_error if the last error was
 * caused by malformed UTF-8 data (only when running a regex in UTF-8 mode). Available
 * since PHP 5.2.0.
 * @link http://php.net/manual/en/pcre.constants.php
 */
define ('PREG_BAD_UTF8_ERROR', 4);

However, you should really not use regex to parse html. Use DOMDocument

EDIT: Also I don't think this answer would be complete without including You can't parse [X]HTML with regex.

Your #4 error is a "PREG_BAD_UTF8_ERROR", you should check charset used on sites wich caused this error.

It is possible that you exceeded backtrack and/or internal recursion limits. See http://php.net/manual/en/pcre.configuration.php

Try this before preg_replace:

ini_set('pcre.backtrack_limit', '10000000');
ini_set('pcre.recursion_limit', '10000000');