Delete blank lines in vim

Thanks to stackoverflow for this one.

:g/^$/d will delete all blank lines in a file

Why? Because :g will execute a command on lines which match the regex and :d deletes :)

Put the results of a command in the current vim buffer

:r will read a file into the current buffer in vim
:! will execute a command
You can use them together to read the results of a command and put them in the current buffer
e.g. :r ! ls -1 /home/user/directory | sort -r