干掉文件末尾的^M ( remove trailing ^M characters )

refer to: http://stackoverflow.com/questions/811193/how-to-convert-the-m-linebreak-to-normal-linebreak-in-a-file-opened-in-vim

Within vim, look at the file format — DOS or Unix:

方法1. 

:set filetype=unix

:set fileformat=unix

The file will be written back without carriage return (CR, ^M) characters.

方法2。 （2025.11)

:e ++ff=dos | setl ff=unix | up