Command line subcommands

Context

For complex CLI tools (like git with git add, git commit), you need subcommands. The flag package alone is not enough; you can implement subcommands by using flag.NewFlagSet for each subcommand.

Example

A simple CLI with add and list subcommands.

Code example

package main

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

func main() {
    if len(os.Args) < 2 {
        fmt.Println("Expected 'add' or 'list' subcommand")
        os.Exit(1)
    }

    switch os.Args[1] {
    case "add":
        addCmd := flag.NewFlagSet("add", flag.ExitOnError)
        task := addCmd.String("task", "", "task description")
        addCmd.Parse(os.Args[2:])
        fmt.Printf("Adding task: %s\n", *task)

    case "list":
        listCmd := flag.NewFlagSet("list", flag.ExitOnError)
        all := listCmd.Bool("all", false, "list all tasks")
        listCmd.Parse(os.Args[2:])
        fmt.Printf("Listing tasks (all=%v)\n", *all)

    default:
        fmt.Println("Unknown subcommand")
        os.Exit(1)
    }
}

Output

Adding task: buy milk
Listing tasks (all=true)

Useful links

• flag.NewFlagSet documentation
• Go by Example: Command-Line Subcommands