替換字符串PHP詞多次出現

Question

我只是想替換以下字符串：

This is my first sentence. 
.:. 
This is my second sentence. 
.:. 
This is my third sentence. 
.:. 

輸出應該是這樣的：

This is my first sentence. 
1 
This is my second sentence. 
2 
This is my third sentence. 
3 

我怎麼能做到這一點的更有效，更容易辦法？

Answer 1

echo preg_replace_callback("/@/", 
    function(){static $count=0; return ++$count;}, 
    "A@B@C@");