Flago

🐉 Simple and Flexible Command line flag parser

Install ⭐️

go get github.com/Gers2017/flago

Basic Usage 🔥

Import flago

import (
    "github.com/Gers2017/flago"
)

Populate the flagset

get := flago.NewFlagSet("get")
get.Bool("all", false)
get.Switch("verbose") // Same as get.Bool("verbose", false)

Builder

get := flago.NewFlagSet("get").
    Bool("all", false).
    Switch("verbose") // Same as get.Bool("verbose", false)

Using the Cli struct

cli := flago.NewCli()
cli.Handle(get, func(fs *flago.FlagSet) error {
    HandleFlagset(fs) // do something with parsed get
    return nil
})

if err := cli.Execute(os.Args); err != nil {
    log.Fatal(err)
}

func HandleFlagset(fs *flago.FlagSet) {
    if fs.Bool("help") {
		fmt.Println("Some helpful help message")
		return
	}

    // Do something...
    fmt.Println(todos)
}

Without the Cli struct

Parse the arguments into flags

// os.Args = []string{ "cli", "all", "help" }
if err := get.ParseFlags(os.Args[1:]); err != nil {
    log.Fatal(err)
    return
}

Then use the parsed flagset

if get.IsParsed("all") {
    if get.Bool("help") {
        fmt.Println("Some helpful help message")
        return
    }
    // Do something...
    fmt.Println(todos)
}

Demo 🐲

A complete example can be found here

New FlagSet

get := flago.NewFlagSet("get")

Add flags

get.SetSwitch("verbose")
get.Int("x", 0)

Check if a flag was parsed

It's highly recommended to use this method to check first if a flag was parsed correctly.

get.IsParsed("your-flag-name")

The FlagSet.[Bool, Int, Float, Str] methods are just a shortcut for:

Get values

verbose := get.Bool("verbose")
x := get.Int("x")

If the flag name inside the getter method is not registered in the flagset, you'll get an error at runtime.

wrong := get.Bool("some-invalid-flag")

About the API

Why so many strings? Isn't that error-prone?

1. The FlagSet.[Bool, Int, Float, Str] method can raise an error at runtine (use FlagSet.IsParsed to avoid this)

2. A note on golang's generics Behind the scenes flago uses maps + generics + type parsing The Flag struct contains a Value property of type any.

   Because if we try to use generics we'd need to declare a map for every type of flag inside Flagset, and Flags map[string]*Flag wouldn't work anymore leading to repeated code.

   The flag module in the standard library solves this by using pointers to the underliying values.