PHP实现把文本中的URL转换为链接的函数

/**
* Author: SeeDZ
* From: http://code.seebz.net/p/autolink-php/
**/
function autolink($str, $attributes = array()) {
$attrs = '';
foreach ($attributes as $attribute=>$value) {
$attrs .= " {$attribute}=\"{$value}\"";
}
$str = ' '.$str;
$str = preg_replace('`([^"=\'>])((http|https|ftp|ftps)://[^\s< ]+[^\s<\.)])`i', '$1<a href="$2" rel="external nofollow" '.$attrs.'>$2</a>', $str);
$str = substr($str, 1);
return $str;
}

<?php
$str = 'A link : http://example.com/?param=value#anchor.';
$str = autolink($str);
echo $str; // A link : <a href="http://example.com/?param=value#anchor" rel="external nofollow" >http://example.com/?param=value#anchor</a>.
?>

<?php
$str = 'http://example.com/';
$str = autolink($str, array("target"=>"_blank","rel"=>"nofollow"));
echo $str; // <a href="http://example.com/" rel="external nofollow" target="_blank" >http://example.com/</a>
?>