Mindpsill - Technology

You can execute shell commands from vi by typing ! [shell command]. To count the number of words in the current document run the wc (word count) program as a shell command in vi and specify % as the wc argument. The % references the current open file in vi. The file must be saved for this to work otherwise, a file not found exception is returned.

To use the result of any shell output command use the :r! instead of the ! before the shell command. This will append the output of the command to the end of the current open file.

Sources: Vim tips: Working with external commands