:read command to read from an external sources into the current buffer.
Read from File
:read FILENAME to read the content of FILENAME into the current buffer.
Read from Commands
Read can also insert results from external commands. Combine read with
:read ! [shell command] to execute the shell command and insert the output into the current buffer.
An example I use for grabbing the salt for a WordPress config:
:read ! curl --silent https://api.wordpress.org/secret-key/1.1/salt/
Read from curl example
Bash Programming the Vim Way
I will often use the read command to grab a list of files to manipulate. I'm terrible at bash programming and often find it easier to do things the hard way like this:
Not bash programming