Opts

Update 6th December, 2023

The v2 of this library has been released, and you should probably use that instead:

$ go get -u git.sr.ht/~mango/opts/v2

Opts

Opts is a simple Go library implementing unicode-aware getopt(3)- and getopt_long(3) flag parsing in Go. For details, check out the godoc documentation.

Note that unlike the getopt() C function, the ‘:’ and ‘?’ flags are not returned on errors — the errors are instead returned via the err return value of opts.Get() and opts.GetLong(). Additionally, a leading ‘:’ in the opt-string provided to opts.Get() is not supported; you are responsible for your own I/O.

Example Usage

The following demonstrates an example usage of the opts.Get() function…

package main

import (
    "fmt"
    "os"

    "git.sr.ht/~mango/opts/v2"
)

func usage() {
    fmt.Fprintf(os.Stderr, "Usage: %s [-ßλ] [-a arg]\n", os.Args[0])
    os.Exit(1)
}

func main() {
    flags, rest, err := opts.Get(os.Args, "a:ßλ")
    if err != nil {
        fmt.Fprintf(os.Stderr, "%s: %s\n", os.Args[0], err)
        usage()
    }

    for _, f := range flags {
        switch f.Key {
        case 'a':
            fmt.Println("-a given with argument", f.Value)
        case 'ß':
            fmt.Println("-ß given")
        case 'λ':
            fmt.Println("-λ given")
        }
    }

    fmt.Println("The remaining arguments are:", rest)
}

…and the following demonstrates an example usage of the opts.GetLong() function:

package main

import (
    "fmt"
    "os"

    "git.sr.ht/~mango/opts"
)

func usage() {
    fmt.Fprintf(os.Stderr, "Usage: %s [-ßλ] [-a arg] [--no-short]\n", os.Args[0])
    os.Exit(1)
}

func main() {
    // The fourth long-option has no short-option equivalent
    flags, rest, err := opts.GetLong(os.Args, []opts.LongOpt{
        {Short: 'a', Long: "add", Arg: opts.Required},
        {Short: 'ß', Long: "sheiße", Arg: opts.None},
        {Short: 'λ', Long: "λεωνίδας", Arg: opts.None},
        {Short: -1, Long: "no-short", Arg: opts.None},
    })
    if err != nil {
        fmt.Fprintf(os.Stderr, "%s: %s\n", os.Args[0], err)
        usage()
    }

    for _, f := range flags {
        switch f.Key {
        case 'a':
            fmt.Println("-a or --add given with argument", f.Value)
        case 'ß':
            fmt.Println("-ß or --sheiße given")
        case 'λ':
            fmt.Println("-λ or --λεωνίδας given")
        case -1:
            fmt.Println("--no-short given")
        }
    }

    // The remaining arguments
    fmt.Println("The remaining arguments are:", rest)
}