如何修复此字符串替换php问题？(How to fix this string replace php problem?)

 我想用链接替换单词（不包括：，。。stc。）。 我怎样才能做到这一点？ 
 
<?php
$string = "wordey; string, boom";
$string = preg_replace("/[^a-z]/i", "<a href='x'>/[^a-z]/i</a>", $string); //??
echo $string; // <a href='wordey'>wordey</a>; <a href='string'>string</a>, <a href='boom'>boom</a>
?>
 
 请注意; ，。 - 等等很重要。 

I want to replace the words(excluding: , ; . stc.) with links. How can I do this?
 
<?php
$string = "wordey; string, boom";
$string = preg_replace("/[^a-z]/i", "<a href='x'>/[^a-z]/i</a>", $string); //??
echo $string; // <a href='wordey'>wordey</a>; <a href='string'>string</a>, <a href='boom'>boom</a>
?>
 
Please note that the ; , . - etc are important. 

原文：https://stackoverflow.com/questions/6946757