runtimeterror/content/posts/read-content-into-file-vim/index.md

title	date	draft	description	featured	toc	reply	categories	tags
Read Content Into a File with Vim	2024-12-10 21:42:17-06:00	false	Using Vim's :r[ead] command to import content from another file or insert command output without leaving the editor.	false	true	true	Tips	linux shell

I've been comfortable working with Vim for what feels like ages, but I still regularly learn about features and capabilities I'd overlooked.

I recently discovered Vim's :r[ead] command which makes it easy to insert data from another file. I put this to use when I was configuring Netplan on a Linux VM while connected through a remote console session (without copy/paste support) and needed to include an interface's MAC address. Through the magic of Vim, I was able to pull that data straight into the file. For example:

network:
  ethernets:
    ens18:
      [...]
      match:
        macaddress: # and then I entered...
`<Esc>:r /sys/class/net/ens18/address<CR>`

I hit <Esc> to switch to normal mode, invoked the :r[ead] command, and pointed it to the /sys file which holds the MAC address for the interface. The address was then inserted straight into the file:

network:
  ethernets:
    ens18:
      [...]
      match:
        macaddress:
de:ad:be:ef:ca:fe # [tl! ~~]

:r[ead] inserts the extracted content on the line after the cursor so I just needed to quickly back it up to the macaddress line but that was still a pretty easy exercise.

network:
  ethernets:
    ens18:
      [...]
      match:
        macaddress: de:ad:be:ef:ca:fe # [tl! ~~]

This approach also works well for capturing output from a command with :r !command, such as generating a random password for a Docker Compose stack:

services:
  my_app:
    [...]
    environment:
      DB_SECRET:
`<Esc>:r !apg -M NCL -m 32 -a 1 -n 1`

would yield something like:

services:
  my_app:
    [...]
    environment:
      DB_SECRET:
Cn6kp5y2BBk0VvAisULO4dxkXaGyFJ4f # [tl! ~~]

And again just a quick bit of rearranging...

services:
  my_app:
    [...]
    environment:
      DB_SECRET: Cn6kp5y2BBk0VvAisULO4dxkXaGyFJ4f # [tl! ~~]

Being able to merge in data from elsewhere without leaving the editor is a pretty slick trick, don't you think?