`shellcheck` and You Should Too

#linux #devops #tutorial #bash

I'll start off by saying it's been a while since I've been a traditional sysadmin.
I've transitioned over the last few years from "Production Engineer" to "DevOps Engineer" then to a talking head AKA Developer Advocate. (That's supposed to be tongue and cheek, but keeping technical as a Developer Advocate is HARD.) I do still write some code and scripts, but all in all I don't have a production environment to care and feed for. I'll say this, I miss it, and maybe one day I'll go back to help run a team, but right now I'm not in the right career place.

But I digress; this post is about shellcheck and the power that can come of it. As a Developer Advocate, I write a lot of code that glues things together, being I spend my time on Linux and Mac, bash is the obvious choice. I started talking to people at different conferences I go to, and the idea of linting code is still considered a Developer practice instead of an Operator practice. I'm here to try to set the record straight.

Why?

First thing first, why. Standardizing on coding practices, and yes you now code, will save you from insane overhead and tech debt in the future. When your teams' bash scripts start to look the same, it's easier to read, and with that, people start paying attention to what's happening instead of where the do or the ; is; shellcheck enforces this. I should say, you can over ride these in shellcheck but that's a team decision and out of scope of this post. (Read up here if you need to go down this path.)

How?

Now we come to how. There's a handful of ways to get it, apt, yum, homebrew and even a docker container can be ran to run this application. It's really easy to add to your CI/CD pipeline too, pulling out every .sh file, and running shellcheck against it.

Adding it to your Makefile is simple:

check-scripts:
    # Fail if any of these files have warnings
    shellcheck myscripts/*.sh

And even Travis CI, has it built in with just adding this to your .travis.yml:

script:
  # Fail if any of these files have warnings
  - shellcheck myscripts/*.sh

Personally I use the docker container on my local laptop. I wrote a simple script that I named shellcheck.sh and any time I save a script .sh I run shellcheck.sh script.sh against it. As you can see, it's very straight forward.

#!/bin/bash

if [ $# -eq 0 ]
  then
    echo "You need to add an script to this check, shellcheck.sh script.sh"
    exit 1
else
  if [[ "$(ping www.google.com -c 1 | grep '100% packet loss' )" != "" ]]
  then
    echo "You can't seem to connect to the internet, you should proobly fix that."
    exit 1
  fi
  docker pull koalaman/shellcheck:latest
  docker run -v "$PWD:/mnt" koalaman/shellcheck "$1"
fi

It gives me a piece of mind that my code all is standardized and just "works" as expected. The output of shellcheck also tells you exactly why your offending code is, with a dedicated wiki page here with some very explicit why you shouldn't do it this way.
I applaud the main developer Vidar Holen and team to help make use better developers.

Wrap Up

Honestly, I'm just here to convince you, dear reader, to give this linter a shot. The overhead is minimal, and the benefits are immense. This is one of those things that you shouldn't waste time on debating, it will just make your life, and your team's life easier. You can get it into CI, run locally and make sure everyone writes their scripts with a unified pattern with only a tad bit of work.

NOTE: Yes, I ran the above script through shellcheck too.