cli: Command Line Interface Made Simpler

The cli package provides a framework-agnostic way to define command-line interfaces in Go. Its primary goal is to decouple your application's CLI logic from specific CLI frameworks like spf13/cobra or urfave/cli. This allows for easier testing, greater flexibility, and the ability to switch between underlying CLI frameworks without significant code changes.

Motivation

Existing CLI frameworks, while powerful, often lead to tight coupling. Changing frameworks can require extensive rewrites.

cli aims to solve this by:

• Abstraction: Providing a simple, consistent interface for defining commands.
• Testability: Making it easy to test command logic in isolation, without framework dependencies.
• Flexibility: Allowing you to choose (and change) the underlying CLI framework that best suits your needs.
• Simplicity: Focusing on core CLI functionality, avoiding unnecessary complexity.

Usage

Basic Command

The simplest command implements the Command interface:

package main

import (
    "context"
    "os"

    "github.com/krostar/cli"
    spf13cobra "github.com/krostar/cli/mapper/spf13/cobra"
)

type myCommand struct{}

func (myCommand) Execute(ctx context.Context, args []string, dashedArgs []string) error {
    // Your command logic here.
    // args: Positional arguments.
    // dashedArgs: Arguments after a "--".
    return nil
}

func main() {
    cmd := cli.New(myCommand{})
    err := spf13cobra.Execute(context.Background(), os.Args, cmd)
    cli.Exit(context.Background(), err)
}

Adding Subcommands

type subCommand struct{}

func (subCommand) Execute(ctx context.Context, args []string, dashedArgs []string) error {
    // Subcommand logic.
    return nil
}

func main() {
    cmd := cli.New(myCommand{}).AddCommand("sub", subCommand{}) // Add a subcommand named "sub".

    // Or, mount a complete CLI as a subcommand:
    subCLI := cli.New(subCommand{})
    cmd.Mount("another", subCLI)

    err := spf13cobra.Execute(context.Background(), os.Args, cmd)
    cli.Exit(context.Background(), err)
}

Flags

type flagCommand struct {
    name string
    age  int
    tags []string
}

func (c *flagCommand) Flags() []cli.Flag {
    return []cli.Flag{
        cli.NewBuiltinFlag("name", "", &c.name, "Your name"),
        cli.NewBuiltinFlag("age", "", &c.age, "Your age"),
        cli.NewBuiltinSliceFlag("tags", "t", &c.tags, "Comma-separated tags"),
    }
}

func (c *flagCommand) Execute(ctx context.Context, args []string, dashedArgs []string) error {
    // Access flag values: c.name, c.age, c.tags
    return nil
}

Hooks

type hookedCommand struct{}

func (hookedCommand) Execute(ctx context.Context, args []string, dashedArgs []string) error {
    // command logic
    return nil
}

func (c hookedCommand) Hook() *cli.Hook {
    return &cli.Hook{
        BeforeCommandExecution: func(ctx context.Context) error {
            // Code to run before Execute.
            return nil
        },
        AfterCommandExecution: func(ctx context.Context) error {
            // Code to run after Execute.
            return nil
        },
    }
}

Signal Handling

func main() {
    ctx, cancel := cli.NewContextCancelableBySignal(syscall.SIGINT, syscall.SIGTERM)
    defer cancel()

    err := spf13cobra.Execute(ctx, os.Args, /* ... */)
    cli.Exit(ctx, err)
}

Configuration Management

The cli package provides a powerful configuration system through the cfg package that allows loading configuration from multiple sources with precedence.

Configuration Sources

The following sources are supported out of the box:

• Default Values: Set default values for your configuration
• Environment Variables: Load configuration from environment variables
• Configuration Files: Load configuration from YAML/JSON files
• Command-line Flags: Load configuration from command-line flags

Configuration Example

import (
    "github.com/krostar/cli"
    clicfg "github.com/krostar/cli/cfg"
    "github.com/krostar/cli/cfg/source/default"
    "github.com/krostar/cli/cfg/source/env"
    "github.com/krostar/cli/cfg/source/file"
    "github.com/krostar/cli/cfg/source/flag"
)

// Config structure with environment variable mappings
type Config struct {
    Server struct {
        Host string `env:"SERVER_HOST"`
        Port int    `env:"SERVER_PORT"`
    }
    LogLevel   string `env:"LOG_LEVEL"`
    ConfigFile string `env:"CONFIG_FILE"`
}

// SetDefault implements the default values
func (cfg *Config) SetDefault() {
    cfg.Server.Host = "localhost"
    cfg.Server.Port = 8080
    cfg.LogLevel = "info"
    cfg.ConfigFile = "config.yaml"
}

// Command with configuration
type MyCommand struct {
    config Config
}

// Define flags that map to your configuration
func (cmd *MyCommand) Flags() []cli.Flag {
    return []cli.Flag{
        cli.NewBuiltinFlag("config", "c", &cmd.config.ConfigFile, "Path to config file"),
        cli.NewBuiltinFlag("host", "", &cmd.config.Server.Host, "Server host"),
        cli.NewBuiltinFlag("port", "p", &cmd.config.Server.Port, "Server port"),
        cli.NewBuiltinFlag("log-level", "l", &cmd.config.LogLevel, "Log level"),
    }
}

// Use hooks to load configuration in order of precedence
func (cmd *MyCommand) Hook() *cli.Hook {
    return &cli.Hook{
        BeforeCommandExecution: clicfg.BeforeCommandExecutionHook(
            &cmd.config,
            // Sources are applied in order, with later sources taking precedence
            sourcedefault.Source[Config](),                              // 1. Defaults
            sourcefile.Source(getConfigFilePath, yamlUnmarshaler, true), // 2. Config file
            sourceenv.Source[Config]("APP"),                             // 3. Environment variables
            sourceflag.Source[Config](cmd),                              // 4. Command-line flags
        ),
    }
}

License

This project is licensed under the MIT License - see the LICENSE file for details.