正则，如果img标签里没有alt，则加上alt=""
正则，如果img标签里没有alt，则加上alt= " "

<img   src= "asdfas.gif "   width= " "         heigth= " "   alt= "dsafa ">
-->
<img   src= "asdfas.gif "   width= " "         heigth= " "   alt= "dsafa ">

<img   src= "asdfas.gif "   width= " "         heigth= " ">
-->
<img   src= "asdfas.gif "   width= " "         heigth= " "   alt= "dsafa ">

意思就是，有的话不管，没有则加上一个


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DC关注
------解决方案--------------------
( <img(?![^\x3E]*?alt[^\x3E]*?> ).*?)> 
可以吗？
------解决方案--------------------
jf