`:read` the output of a command into the current buffer
If you want to use the output of a command inside your file, you don’t need
to exit Vim, run the command, copy the output, return to Vim and paste the
contents. You can use :read (or abbreviated to :r) and run a command
with !. For example, :r !ls -a will insert the output of ls -a at
the current cursor position.
You can also insert the content of another file with :r, except this time
you don’t use !, just the file name. For example, :r second_file will
insert the content of second_file at the current cursor position.