Programming language: Go
License: MIT License
Tags: Command Line     Standard CLI    

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CLIF - Command line interface framework

Go framework for rapid command line application development.



package main

import "gopkg.in/ukautz/clif.v0"

func main() {
    c := cli.New("My App", "1.0.0", "An example application").
        New("hello", "The obligatory hello world", func(out cli.Output) {
            out.Printf("Hello World\n")


$ go get gopkg.in/ukautz/clif.v0

Getting started

One the one side, CLIF's builder-like API can be easily used for rapid development of small, single purpose tools. On the other side, CLIF is designed with complex console applications in mind.

clif.New("My App", "1.0.0", "An example application").
    New("ls", "", func() { fmt.Printf("Foo\n") }).
    New("bar", "", func() { fmt.Printf("Bar\n") }).


Commands must have a unique name and can have additional arguments and options.

cmd1 := cli.NewCommand("name", "A description", callBackFunction)
cmd2 := cli.NewCommand("other", "Another description", callBackFunction2)

The name is used from the command line to call the command:

$ ./app name
$ ./app other

Callback functions

Callback functions can have arbitrary parameters. CLIF uses a small, built-in dependency injection container which allows you to register any kind of object (struct or interface) beforehand.

CLIF pre-populates the dependency container with a couple of built-in objects:

  • The Output (formatted output helper, see below)
  • The Input (input helper, see below)
  • The *Cli instance itself
  • The current *Command instance
package main

import "gopkg.in/ukautz/clif.v0"

type MyFoo struct {}

// ... MyFoo implementation

func callMe(out clif.Output, foo *MyFoo) {
    out.Printf("Foo: %s\n", foo)

func main() {
    cli := clif.New("my-app", "My kewl App", "0.8.5").
        New("call", "Call me", callMe).

If you want to register an interface, you need to use the Go'ish way:

package main

import "gopkg.in/ukautz/clif.v0"

// the interface
type MyFoo interface {
    Bar() string

// the struct implementing the interface
type MyBar struct {}

// ... MyBar implementation

func callMe(out clif.Output, foo MyFoo) {
    out.Printf("Foo: %s\n", foo)

func main() {
    t := reflect.TypeOf((*MyFoo)(nil)).Elem()
    cli := clif.New("my-app", "My kewl App", "0.8.5").
        New("call", "Call me", callMe).
        RegisterAs(t.String(), new(MyBar))

Arguments and Options

CLIF can deal with arguments and options. The difference being:

  • Arguments come after the command name. They are identified by their position.
  • Options have no fixed position. They are identified by their --opt-name (or alias, eg -O)

Of course you can use arguments and options at the same time..


Arguments are additional command line parameters which come after the command name itself.

cmd := cli.NewCommand("hello", "A description", callBackFunction)
    .NewArgument("name", "Name for greeting", "", true, false)

arg := clif.NewAgument("other", "Something ..", "default", false, true)

Arguments consist of a name, a description, an optional default value a required flag and a multiple flag.

$ ./my-app hello the-name other1 other2 other3
#            ^      ^       ^       ^     ^
#            |      |       |       |     |
#            |      |       |       | third "other" arg
#            |      |       |  second "other" arg
#            |      |  first "other" arg
#            |  the "name" arg
#        command name

Position of arguments matters. Make sure you add them in the right order. And: required arguments must come before optional arguments (makes sense, right?). There can be only one multiple argument at all.

You can access the arguments by injecting the command instance into the callback and calling the Argument() method. You can choose to interpret the argument as String(), Int(), Float(), Bool(), Time() or Json(). Multiple arguments can be accessed with Strings(), Ints() .. and so on. Count() gives the amount of (provided) multiple arguments and Provided() returns bool for optional arguments. Pleas see [parameter.go](parameter.go) for more.

func callbackFunctionI(c *clif.Command) {
    name := c.Argument("name").String()
    others := c.Argument("other").Strings()
    // .. do something ..

Options have no fixed position. They are referenced by their name (eg --name) or alias (eg -n).

cmd := cli.NewCommand("hello", "A description", callBackFunction)
    .NewOption("name", "n", "Name for greeting", "", true, false)

arg := clif.NewOption("other", "O", "Something ..", "default", false, true)


$ ./my-app hello --other bar -n Me -O foo
#                       ^       ^    ^
#                       |       |    |
#                       |       |  second other opt
#                       |   name opt
#                  first other opt

You can access options the same way as arguments, just use Option() instead.

func callbackFunctionI(c *clif.Command) {
    name := c.Option("name").String()
    others := c.Option("other").Strings()
    // .. do something ..

There is a special kind of option, which does not expect a parameter: the flag.

flag := clif.NewOption("my-flag", "f", "Something ..", "", false, false).IsFlag()
cmd := cli.NewCommand("hello", "A description", callBackFunction).AddOption(flag)

Usually, you want to use Bool() on flags:

func callbackFunctionI(c *clif.Command) {
    if c.Option("my-flag").Bool() {
        // ..

You can provide argument or option validators, which are executed on parsing the command line input, before it is delegated to your callback.

arg := clif.NewArgument("my-int", "An integer", "", true, false)
arg.SetValidator(func(name, value string) error {
    if _, err := strconv.Atoi(value); err != nil {
        return fmt.Errorf("Oops: %s is not an integer: %s", name, err)
    } else {
        return nil

There are a couple of built-in validators you can use out of the box:

  • clif.IsInt - Checks for integer
  • clif.IsFloat - Checks for float

See [validators.go](validators.go).

Input & Output

Of course, you can just use fmt and os.Stdin, but for convenience (and fancy output) there are clif.Output and clif.Input.

func callbackFunctionI(in clif.Input, out clif.Output) {
    name := in.Ask("Who are you? ", func(v string) error {
        if len(v) > 0 {
            return nil
        } else {
            return fmt.Errorf("Didn't catch that")
    father := in.Choose("Who is your father?", map[string]string{
        "yoda":  "The small, green guy",
        "darth": "NOOOOOOOO!",
        "obi":   "The old man with the light thingy",

    out.Printf("Well, %s, ", name)
    if father != "darth" {
        out.Printf("<success>may the force be with you!<reset>\n")
    } else {
        out.Printf("<error>u bad!<reset>\n")


Customizing Input

There is not much. Check out RenderChooseQuestion, RenderChooseOption and RenderChooseQuery in [input.go](input.go).

Extending Output

Output comes with a set of tokens, such as <success> or <error>, which inject ASCII color codes into the output stream. If you don't want fancy colors, you can just:

cli := clif.New("my-app", "0.1.0", "Boring output")

To extend or change the fancy style, please modify clif.DefaultStyles in [formatter.go](formatter.go).

See also

There are a lot of other approaches you should have a look at.