[Linux 常見問題] How do I rename the extension for a batch of files?

Source From Here 
Question 
In a directory, I have a bunch of *.html files. I'd like to rename them all to *.txt by using the bash shell. 

How-To 
- test.sh 

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1. #!/bin/sh  
2. for file in *.html; do  
3.     new_ft=${file%*.html}  
4.     echo "$new_ft"  
5.     mv "$file" "${new_ft}.txt"  
6. done  

Supplement 
* How do I rename the extension for a batch of files? 
* 鳥哥 - 認識與學習 BASH: 變數內容的刪除、取代與替換