replace all occurrences of a string - php

Question

I want to add a class to all p tags that contain arabic text in it. For example:
<p>لمبارة وذ</p>
<p>do nothing</p>
<p>خمس دقائق يخ</p>
<p>مراعاة إبقاء 3 لاعبين</p>
should become
<p class="foo">لمبارة وذ</p>
<p>do nothing</p>
<p class="foo">خمس دقائق يخ</p>
<p class="foo">مراعاة إبقاء 3 لاعبين</p>
I am trying to use PHP preg_replace function to match the pattern (arabic) with following expression:
preg_replace("~(\p{Arabic})~u", "<p class=\"foo\">$1", $string, 1);
However it is not working properly. It has two problems:
It only matches the first paragraph.
Adds an empty <p>.
Sandbox Link

Answer 1

It only matches the first paragraph.
This is because you added the last argument, indicating you want only to replace the first occurrence. Leave that argument out.
Adds an empty <p>.
This is in fact the original <p> which you did not match. Just add it to the matching pattern, but keep it outside of the matching group, so it will be left out when you replace with $1.
Here is a corrected version, also on sandbox:
$text = preg_replace("~<p>(\p{Arabic}+)~u", "<p class=\"foo\">$1", $string);

Answer 2

Your first problem is that you weren't telling it to match the <p>, so it didn't.
Your main problem is that spaces aren't Arabic. Simply adding the alternative to match them fixes your problem:
$text = preg_replace("~<p>(\p{Arabic}*|\s*)~u", "<p class=\"foo\">$1", $string);

Answer 3

Using DOMDocument and DOMXPath:
$html = <<<'EOD'
<p>لمبارة وذ</p>
<p>خمس دقائق يخ</p>
<p>مراعاة إبقاء 3 لاعبين</p>
EOD;
libxml_use_internal_errors(true);
$dom = new DOMDocument;
$dom->loadHTML('<div>'.$html.'</div>', LIBXML_HTML_NOIMPLIED);
$xpath = new DOMXPath($dom);
// here you register the php namespace and the preg_match function
// to be able to use it in the XPath query
$xpath->registerNamespace("php", "http://php.net/xpath");
$xpath->registerPhpFunctions('preg_match');
// select only p nodes with at least one arabic letter
$pNodes = $xpath->query("//p[php:functionString('preg_match', '~\p{Arabic}~u', .) > 0]");
foreach ($pNodes as $pNode) {
$pNode->setAttribute('class', 'foo');
}
$result = '';
foreach ($dom->documentElement->childNodes as $childNode) {
$result .= $dom->saveHTML($childNode);
}
echo $result;