At Magnetis we are moving our cloud infrastructure to Kubernetes. To do so I started creating a bunch of shell scripts inside our app. There is no problem with it, but as soon as i got 5 different shell script files it started to get messy.
In one of pair programming sessions that we do in our hiring process, a candidate chose Thor to write the test project. It was organized and seemed easy to get started. So connecting the dots I thought that our scripts probably would be much more expressive with Thor.
Command lines are already part of our everyday living: git, bundler and rails to name a few. Creating one helps you to organize and better share the utilities for daily work.
In this article we will write a simple example inspired by one of the best Breaking Bad scenes. But apart of its simplicity, it is the same process to create a CLI for really anything you want.
Let’s get started by creating a new gem, that will make it easier to distribute our software, in this case the executable file.
To create a new gem, bundler has a handy command (bundler itself is crafted with Thor):
$ bundle gem --exe walter This will generate a skeleton as follows: create walter/Gemfile create walter/lib/walter.rb create walter/lib/walter/version.rb create walter/walter.gemspec create walter/Rakefile create walter/README.md create walter/bin/console create walter/bin/setup create walter/.gitignore create walter/.travis.yml create walter/.rspec create walter/spec/spec_helper.rb create walter/spec/walter_spec.rb create walter/LICENSE.txt create walter/exe/walter
Now we need to add the Thor as a dependency to our project, open up walter.gemspec and add:
spec.add_dependency "thor", "~> 0.20"
We will also need to remove the TODO items in the gemspec file, so go ahead and edit the values for summary, description and homepage. Run the bundle install command and it is all setup to write some Thor lines.
Open up lib/walter.rb and let’s add some code, first thing you need to require and inherit from Thor:
require 'walter' require 'thor' module Walter class CLI < Thor # ... end end
Now, let’s add a simple hello world:
class CLI < Thor desc "hello world", "my first cli yay" def hello puts "Hello world" end end
Come on, hello world in 2017? Let’s make it a Hello Heisenberg!
class CLI < Thor desc "hello [name]", "say my name" def hello(name) if name == "Heisenberg" puts "you are goddman right" else puts "say my name" end end end
We are almost there, last thing is to call our lib from the binary file.
The exe directive we used to create the gem, generated a walter binary at our project. First thing you need to do is to change the permissions so we can actually execute the file:
chmod +x exe/walter
Now, we are able to call it:
$ bundle exec exe/walter
This will give no output, but don’t worry. This is expected. Open up exe/walter in your favorite editor and let’s append this:
We are calling the CLI we just created, and passing the arguments received. Now let’s call it again:
$ bundle exec exe/walter walter hello [name] # say hello walter help [COMMAND] # Describe available commands or one specific command
Thor list all the commands this CLI has available, so sweet.
If you try to call our hello command without the name:
$ bundle exec exe/walter hello ERROR: “walter hello was called with no arguments Usage: “walter hello [name]”
Yeah, it tell us how to use it. Making this in shell script would require some conditionals, but Thor has this built-in.
$ bundle exec exe/walter hello Heisenberg you are goddman right.
To install the gem to your system, this way you can it it from anywhere:
$ rake install
$ walter hello Jesse say my name
If you want to release it to rubygems, just run:
$ rake release
The Ruby ecosystem is beautiful, isn’t it?
Thor makes daily scripts much more expressive and meaningful. It is a nice addition to a team that is already using Ruby as an official language, since all the team members can contribute to make your commands even better.
In our case, it was used to create commands to bring up kubernetes clusters and to deploy our app for the staging environment. You can use to automate some internal process or workflow you have in your company!
To finish this up, some final tips:
- whenever possible try to use command methods that are common to other CLIs: init, status, new, create, update.
- try to expose as CLI the least amount of methods possible, so you can encapsulate things that are only needed inside the code.
- if you need to write some config file use
If you want to go deeper into the subject, here are the official docs.
Previously posted at medium