$re = '/background:\s*#[a-fA-F0-9]*;/';
$str = '.foo {
background:#ffffgg;
}
.bar {
background: #BADA55;
}
.baz {
background: #fff;
}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php