While working on a small CLI for encrypting and decrypting files, I found myself unstatisfied with the practice of writing, and testing, and reasoning about a CLI in Go. The flag package was not pleasant to work with. Testing was hard and inelegant, and the whole concept of a CLI is leaky. So I pulled out my hair, and cursed at the sky.
Then, I distilled the problem down its constiuent parts, and wrapped them in Flargs. At it’s heart, Flargs is a very simple framework that forces you to do a few things, and in return gives you ease, power, and reproducibility. This is the Hermetic promise: If you never touch the world, you will become divine.
Flargs has three run-time phases:
Parsing. This execution phase gives you no access to your command or the environment it will run against. All you have is a “Konf”, a []string{}, and the logic to turn the latter into the former. If you return an error here, the program stops.
Loading. In this phase you do have access to the environment. Here you can decide if you Konf makes sense in this environment. For instance, you can check to see that a file actually exists. If you return an error, execution stops.
Running. This is actually what makes your CLI useful. The run phase has no access to the original []string{}. It has a Konf and an Environment.
Read Moar: seanmacdonald.ca/posts/flargs