Building CLI Tools in Go

Go is a strong fit for command-line tools because it produces fast, portable binaries and has a capable standard library.

Start with a small command boundary

Keep argument parsing and process orchestration near main, while placing the actual work in testable functions:

package main

import (
	"fmt"
	"os"
)

func run(args []string) error {
	if len(args) == 0 {
		return fmt.Errorf("usage: tool <name>")
	}

	fmt.Println("hello", args[0])
	return nil
}

func main() {
	if err := run(os.Args[1:]); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

Design guidelines

• Write useful errors to standard error and return non-zero exit codes on failure.
• Support -h and document examples in the command help output.
• Accept input from files, standard input, or arguments where that improves composability.
• Keep output stable when users may pipe it into another command.
• Add table-driven tests for parsing, validation, and error cases.

Build and test the tool with:

go test ./...
go build -o bin/tool ./cmd/tool

As the tool grows, split subcommands into packages and keep shared configuration, logging, and filesystem behavior behind small interfaces.