<?php
$str = <<<EOT
呵呵 http://www.abc.com 呵呵 <img src="http://www.cba.com/a.jig">呵呵呵呵呵呵 <a href=http://www.aabbcc.com>呵呵呵呵呵呵
EOT;echo preg_replace('|[^=\'"](http://[a-z\.]+)|i','<a href="\1" target="_blank">\1</a>', $str);
?> output:呵呵<a href="http://www.abc.com" target="_blank">http://www.abc.com</a> 呵呵 <img src="http://www.cba.com/a.jig">呵呵呵呵呵呵 <a href=http://www.aabbcc.com>呵呵呵呵呵呵
$str = <<<EOT
呵呵 http://www.abc.com 呵呵 <img src="http://www.cba.com/a.jig">呵呵呵呵呵呵 <a href=http://www.aabbcc.com>呵呵呵呵呵呵
EOT;echo preg_replace('|[^=\'"](http://[a-z\.]+)|i','<a href="\1" target="_blank">\1</a>', $str);
?> output:呵呵<a href="http://www.abc.com" target="_blank">http://www.abc.com</a> 呵呵 <img src="http://www.cba.com/a.jig">呵呵呵呵呵呵 <a href=http://www.aabbcc.com>呵呵呵呵呵呵
<?php
$str = <<<EOT
http://www.abc.com 呵呵 <img src="http://www.cba.com/a.jig">呵呵呵呵呵呵 <a href=http://www.aabbcc.com>呵呵呵呵呵呵
EOT;
$str = <<<EOT
http://www.abc.com 呵呵 <img src="http://www.cba.com/a.jig">呵呵呵呵呵呵 <a href=http://www.aabbcc.com>呵呵呵呵呵呵
EOT;echo preg_replace('|[^=\'"]?(http://[a-z\.]+)|i','<a href="\1" target="_blank">\1</a>', $str);
?>