很多图书配备的源码都是txt格式，以前示例直接修改为SQL文件，方便编辑器直接打开
tree /f
ren *.txt *.sql
for /R %x in (*.txt) do ren "%x" *.sql
参考：
Recursively batch rename file extensions
The following command will rename files from one extension to another, in all subfolders:
forfiles /S /M *.ext1 /C "cmd /c rename @file @fname.ext2"
or
FOR /R %f IN (*.kar) DO REN "%f" *.mid
For example, if you want to rename all jpg files to png files, the command would be as below:
forfiles /S /M *.jpg /C "cmd /c rename @file @fname.png"
---
@ECHO OFF PUSHD . FOR /R %%d IN (.) DO ( cd "%%d" IF EXIST *.old-extension ( REN *.old-extension *.new-extension ) ) POPD
