Parse Subcommand Flags

Post Example

Some command-line tools, like the go tool or git have many subcommands, each with its own set of flags.

Examples Filter
Parse Subcommand Flags in Go
by yhuang Go fmt.Println os.Args flag.ExitOnError flag.NewFlagSet os.Exit
The flag package lets us easily define simple subcommands that have their own flags.
package main

import (
    "flag"
    "fmt"
    "os"
)

func main() {

    // We declare a subcommand using the NewFlagSet function,
    // and proceed to define new flags specific for this subcommand.
    fooCmd := flag.NewFlagSet("foo", flag.ExitOnError)
    fooEnable := fooCmd.Bool("enable", false, "enable")
    fooName := fooCmd.String("name", "", "name")

    // For a different subcommand we can define different supported flags.
    barCmd := flag.NewFlagSet("bar", flag.ExitOnError)
    barLevel := barCmd.Int("level", 0, "level")

    if len(os.Args) < 2 {
        fmt.Println("expected 'foo' or 'bar' subcommands")
        os.Exit(1)
    }

    switch os.Args[1] {

    // For every subcommand, we parse its own flags and have access to trailing positional arguments.
    case "foo":
        fooCmd.Parse(os.Args[2:])
        fmt.Println("subcommand 'foo'")
        fmt.Println("  enable:", *fooEnable)
        fmt.Println("  name:", *fooName)
        fmt.Println("  tail:", fooCmd.Args())
    case "bar":
        barCmd.Parse(os.Args[2:])
        fmt.Println("subcommand 'bar'")
        fmt.Println("  level:", *barLevel)
        fmt.Println("  tail:", barCmd.Args())
    default:
        fmt.Println("expected 'foo' or 'bar' subcommands")
        os.Exit(1)
    }
}