- var_dump: documentation ( source)
- preg_replace_callback: documentation ( source)
- trim: documentation ( source)
<?php
$pattern = '/((?<!\w)#\w+)/i';
$subject = <<<EOT
Blablalb #toto zdjsdf #ho_yeah
EOT;
$hashtags = [];
$result = preg_replace_callback('/(\s#\w+)/i', function ($matches) use(&$hastags) {
$hashtags[] = trim($matches[0]);
return '';
}, $subject);
var_dump($result);