$re = '/i:\d+;s:\d+:"([^"]*)";/m';
$str = 'a:4:{i:0;s:4:"a’";i:1;s:6:"abcdef";i:2;s:5:"abcde";i:3;s:3:"xyz";}';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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