Using vi, you want to save changes to the file my file with :w!, but vi complains it cannot write to the file. Therefore, you want to check the write permissions on the file. To do this without leaving vi, you type:

A.
:ls-l myfile

B.
:!ls-I myfile

C.
esc :Is -I myfile

D.
:?ls-l myfile

Explanation:
You can execute the external commands in vi editor using:! command. Example:!ls-l displays all contents of current directory.