I Built a Tiny Go Library to Ignore CLI Flag Ordering

While building a simple QR code generator CLI in Go, I ran into something interesting with the standard flag package.

Consider executing a simple binary in your terminal:

./myBinary -p item

This works as expected.

But:

./myBinary item -p

The -p flag won't be parsed because Go's flag package stops parsing flags once it encounters a positional argument.

I first encountered this behavior while working on that task tracker tool. I wrote a function to brute-force my way around it, but never took the time to understand why it happened.

This time, I did some research and learned that Go's built-in flag parser follows POSIX-style conventions. In simple terms, it expects flags to appear before positional arguments.

Now I understand why it works that way, but I wanted my CLI to behave more like the tools I regularly use.

I mean, both of these work with Git:

git push -f origin main
git push origin main -f

So I built go-os-input-parser.

It's a small, zero-dependency package that separates command-line inputs from flags regardless of where they appear.

For example:

./myBinary item1 -p item2 --config=default.json

The parser can give you:

Inputs: [item1 item2]
Print: true
Config: default.json

You define the flags you want to support, including either or both their short and long forms, and also pass in os.Args[1:]:

inputs := parser.ParseInput(
    os.Args[1:],
    []parser.AllowedBoolTag{
        {
            Short:     "p",
            Long:      "print",
            Container: &print,
        },
    },
    []parser.AllowedStringTag{
        {
            Short:     "c",
            Long:      "config",
            Container: &config,
        },
    },
)

I know there are larger Go CLI libraries like pflag and Cobra, and this might look like reinventing the wheel. But after running into this problem for the second time, I decided to use it as a fun excuse to practice more Go.

I also used this project to improve my testing and documentation. I had an AI agent review the code, point out flaws I had missed, and help me write better unit tests and documentation.

In the end, it's a small project, but a useful go exercise

Here's the github repo: https://github.com/orashus/go-os-input-parser