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	cli
	===

	[![Build Status](https://travis-ci.org/urfave/cli.svg?branch=master)](https://travis-ci.org/urfave/cli)
	[![Windows Build Status](https://ci.appveyor.com/api/projects/status/rtgk5xufi932pb2v?svg=true)](https://ci.appveyor.com/project/urfave/cli)
	[![GoDoc](https://godoc.org/github.com/urfave/cli?status.svg)](https://godoc.org/github.com/urfave/cli)
	[![codebeat](https://codebeat.co/badges/0a8f30aa-f975-404b-b878-5fab3ae1cc5f)](https://codebeat.co/projects/github-com-urfave-cli)
	[![Go Report Card](https://goreportcard.com/badge/urfave/cli)](https://goreportcard.com/report/urfave/cli)
	[![top level coverage](https://gocover.io/_badge/github.com/urfave/cli?0 "top level coverage")](http://gocover.io/github.com/urfave/cli) /
	[![altsrc coverage](https://gocover.io/_badge/github.com/urfave/cli/altsrc?0 "altsrc coverage")](http://gocover.io/github.com/urfave/cli/altsrc)

	Notice: This is the library formerly known as
	`github.com/codegangsta/cli` -- Github will automatically redirect requests
	to this repository, but we recommend updating your references for clarity.

	cli is a simple, fast, and fun package for building command line apps in Go. The
	goal is to enable developers to write fast and distributable command line
	applications in an expressive way.

	<!-- toc -->

	- [Overview](#overview)
	- [Installation](#installation)
	* [Supported platforms](#supported-platforms)
	* [Using the `v2` branch](#using-the-v2-branch)
	* [Pinning to the `v1` releases](#pinning-to-the-v1-releases)
	- [Getting Started](#getting-started)
	- [Examples](#examples)
	* [Arguments](#arguments)
	* [Flags](#flags)
	+ [Placeholder Values](#placeholder-values)
	+ [Alternate Names](#alternate-names)
	+ [Ordering](#ordering)
	+ [Values from the Environment](#values-from-the-environment)
	+ [Values from alternate input sources (YAML, TOML, and others)](#values-from-alternate-input-sources-yaml-toml-and-others)
	* [Subcommands](#subcommands)
	* [Subcommands categories](#subcommands-categories)
	* [Exit code](#exit-code)
	* [Bash Completion](#bash-completion)
	+ [Enabling](#enabling)
	+ [Distribution](#distribution)
	+ [Customization](#customization)
	* [Generated Help Text](#generated-help-text)
	+ [Customization](#customization-1)
	* [Version Flag](#version-flag)
	+ [Customization](#customization-2)
	+ [Full API Example](#full-api-example)
	- [Contribution Guidelines](#contribution-guidelines)

	<!-- tocstop -->

	## Overview

	Command line apps are usually so tiny that there is absolutely no reason why
	your code should not be self-documenting. Things like generating help text and
	parsing command flags/options should not hinder productivity when writing a
	command line app.

	This is where cli comes into play. cli makes command line programming fun,
	organized, and expressive!

	## Installation

	Make sure you have a working Go environment. Go version 1.2+ is supported. [See
	the install instructions for Go](http://golang.org/doc/install.html).

	To install cli, simply run:
	```
	$ go get github.com/urfave/cli
	```

	Make sure your `PATH` includes the `$GOPATH/bin` directory so your commands can
	be easily used:
	```
	export PATH=$PATH:$GOPATH/bin
	```

	### Supported platforms

	cli is tested against multiple versions of Go on Linux, and against the latest
	released version of Go on OS X and Windows. For full details, see
	[`./.travis.yml`](./.travis.yml) and [`./appveyor.yml`](./appveyor.yml).

	### Using the `v2` branch

	Warning: The `v2` branch is currently unreleased and considered unstable.

	There is currently a long-lived branch named `v2` that is intended to land as
	the new `master` branch once development there has settled down. The current
	`master` branch (mirrored as `v1`) is being manually merged into `v2` on
	an irregular human-based schedule, but generally if one wants to "upgrade" to
	`v2` now and accept the volatility (read: "awesomeness") that comes along with
	that, please use whatever version pinning of your preference, such as via
	`gopkg.in`:

	```
	$ go get gopkg.in/urfave/cli.v2
	```

	``` go
	...
	import (
	"gopkg.in/urfave/cli.v2" // imports as package "cli"
	)
	...
	```

	### Pinning to the `v1` releases

	Similarly to the section above describing use of the `v2` branch, if one wants
	to avoid any unexpected compatibility pains once `v2` becomes `master`, then
	pinning to `v1` is an acceptable option, e.g.:

	```
	$ go get gopkg.in/urfave/cli.v1
	```

	``` go
	...
	import (
	"gopkg.in/urfave/cli.v1" // imports as package "cli"
	)
	...
	```

	This will pull the latest tagged `v1` release (e.g. `v1.18.1` at the time of writing).

	## Getting Started

	One of the philosophies behind cli is that an API should be playful and full of
	discovery. So a cli app can be as little as one line of code in `main()`.

	<!-- {
	"args": ["--help"],
	"output": "A new cli application"
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	cli.NewApp().Run(os.Args)
	}
	```

	This app will run and show help text, but is not very useful. Let's give an
	action to execute and some help documentation:

	<!-- {
	"output": "boom! I say!"
	} -->
	``` go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()
	app.Name = "boom"
	app.Usage = "make an explosive entrance"
	app.Action = func(c *cli.Context) error {
	fmt.Println("boom! I say!")
	return nil
	}

	app.Run(os.Args)
	}
	```

	Running this already gives you a ton of functionality, plus support for things
	like subcommands and flags, which are covered below.

	## Examples

	Being a programmer can be a lonely job. Thankfully by the power of automation
	that is not the case! Let's create a greeter app to fend off our demons of
	loneliness!

	Start by creating a directory named `greet`, and within it, add a file,
	`greet.go` with the following code in it:

	<!-- {
	"output": "Hello friend!"
	} -->
	``` go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()
	app.Name = "greet"
	app.Usage = "fight the loneliness!"
	app.Action = func(c *cli.Context) error {
	fmt.Println("Hello friend!")
	return nil
	}

	app.Run(os.Args)
	}
	```

	Install our command to the `$GOPATH/bin` directory:

	```
	$ go install
	```

	Finally run our new command:

	```
	$ greet
	Hello friend!
	```

	cli also generates neat help text:

	```
	$ greet help
	NAME:
	greet - fight the loneliness!

	USAGE:
	greet [global options] command [command options] [arguments...]

	VERSION:
	0.0.0

	COMMANDS:
	help, h Shows a list of commands or help for one command

	GLOBAL OPTIONS
	--version Shows version information
	```

	### Arguments

	You can lookup arguments by calling the `Args` function on `cli.Context`, e.g.:

	<!-- {
	"output": "Hello \""
	} -->
	``` go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Action = func(c *cli.Context) error {
	fmt.Printf("Hello %q", c.Args().Get(0))
	return nil
	}

	app.Run(os.Args)
	}
	```

	### Flags

	Setting and querying flags is simple.

	<!-- {
	"output": "Hello Nefertiti"
	} -->
	``` go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Flags = []cli.Flag {
	cli.StringFlag{
	Name: "lang",
	Value: "english",
	Usage: "language for the greeting",
	},
	}

	app.Action = func(c *cli.Context) error {
	name := "Nefertiti"
	if c.NArg() > 0 {
	name = c.Args().Get(0)
	}
	if c.String("lang") == "spanish" {
	fmt.Println("Hola", name)
	} else {
	fmt.Println("Hello", name)
	}
	return nil
	}

	app.Run(os.Args)
	}
	```

	You can also set a destination variable for a flag, to which the content will be
	scanned.

	<!-- {
	"output": "Hello someone"
	} -->
	``` go
	package main

	import (
	"os"
	"fmt"

	"github.com/urfave/cli"
	)

	func main() {
	var language string

	app := cli.NewApp()

	app.Flags = []cli.Flag {
	cli.StringFlag{
	Name: "lang",
	Value: "english",
	Usage: "language for the greeting",
	Destination: &language,
	},
	}

	app.Action = func(c *cli.Context) error {
	name := "someone"
	if c.NArg() > 0 {
	name = c.Args()[0]
	}
	if language == "spanish" {
	fmt.Println("Hola", name)
	} else {
	fmt.Println("Hello", name)
	}
	return nil
	}

	app.Run(os.Args)
	}
	```

	See full list of flags at http://godoc.org/github.com/urfave/cli

	#### Placeholder Values

	Sometimes it's useful to specify a flag's value within the usage string itself.
	Such placeholders are indicated with back quotes.

	For example this:

	<!-- {
	"args": ["--help"],
	"output": "--config FILE, -c FILE"
	} -->
	```go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Flags = []cli.Flag{
	cli.StringFlag{
	Name: "config, c",
	Usage: "Load configuration from `FILE`",
	},
	}

	app.Run(os.Args)
	}
	```

	Will result in help output like:

	```
	--config FILE, -c FILE Load configuration from FILE
	```

	Note that only the first placeholder is used. Subsequent back-quoted words will
	be left as-is.

	#### Alternate Names

	You can set alternate (or short) names for flags by providing a comma-delimited
	list for the `Name`. e.g.

	<!-- {
	"args": ["--help"],
	"output": "--lang value, -l value.language for the greeting.default: \"english\""
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Flags = []cli.Flag {
	cli.StringFlag{
	Name: "lang, l",
	Value: "english",
	Usage: "language for the greeting",
	},
	}

	app.Run(os.Args)
	}
	```

	That flag can then be set with `--lang spanish` or `-l spanish`. Note that
	giving two different forms of the same flag in the same command invocation is an
	error.

	#### Ordering

	Flags for the application and commands are shown in the order they are defined.
	However, it's possible to sort them from outside this library by using `FlagsByName`
	or `CommandsByName` with `sort`.

	For example this:

	<!-- {
	"args": ["--help"],
	"output": "add a task to the list\n.complete a task on the list\n.\n\n.\n.Load configuration from FILE\n.Language for the greeting."
	} -->
	``` go
	package main

	import (
	"os"
	"sort"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Flags = []cli.Flag {
	cli.StringFlag{
	Name: "lang, l",
	Value: "english",
	Usage: "Language for the greeting",
	},
	cli.StringFlag{
	Name: "config, c",
	Usage: "Load configuration from `FILE`",
	},
	}

	app.Commands = []cli.Command{
	{
	Name: "complete",
	Aliases: []string{"c"},
	Usage: "complete a task on the list",
	Action: func(c *cli.Context) error {
	return nil
	},
	},
	{
	Name: "add",
	Aliases: []string{"a"},
	Usage: "add a task to the list",
	Action: func(c *cli.Context) error {
	return nil
	},
	},
	}

	sort.Sort(cli.FlagsByName(app.Flags))
	sort.Sort(cli.CommandsByName(app.Commands))

	app.Run(os.Args)
	}
	```

	Will result in help output like:

	```
	--config FILE, -c FILE Load configuration from FILE
	--lang value, -l value Language for the greeting (default: "english")
	```

	#### Values from the Environment

	You can also have the default value set from the environment via `EnvVar`. e.g.

	<!-- {
	"args": ["--help"],
	"output": "language for the greeting.*APP_LANG"
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Flags = []cli.Flag {
	cli.StringFlag{
	Name: "lang, l",
	Value: "english",
	Usage: "language for the greeting",
	EnvVar: "APP_LANG",
	},
	}

	app.Run(os.Args)
	}
	```

	The `EnvVar` may also be given as a comma-delimited "cascade", where the first
	environment variable that resolves is used as the default.

	<!-- {
	"args": ["--help"],
	"output": "language for the greeting.LEGACY_COMPAT_LANG.APP_LANG.*LANG"
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Flags = []cli.Flag {
	cli.StringFlag{
	Name: "lang, l",
	Value: "english",
	Usage: "language for the greeting",
	EnvVar: "LEGACY_COMPAT_LANG,APP_LANG,LANG",
	},
	}

	app.Run(os.Args)
	}
	```

	#### Values from alternate input sources (YAML, TOML, and others)

	There is a separate package altsrc that adds support for getting flag values
	from other file input sources.

	Currently supported input source formats:
	* YAML
	* TOML

	In order to get values for a flag from an alternate input source the following
	code would be added to wrap an existing cli.Flag like below:

	``` go
	altsrc.NewIntFlag(cli.IntFlag{Name: "test"})
	```

	Initialization must also occur for these flags. Below is an example initializing
	getting data from a yaml file below.

	``` go
	command.Before = altsrc.InitInputSourceWithContext(command.Flags, NewYamlSourceFromFlagFunc("load"))
	```

	The code above will use the "load" string as a flag name to get the file name of
	a yaml file from the cli.Context. It will then use that file name to initialize
	the yaml input source for any flags that are defined on that command. As a note
	the "load" flag used would also have to be defined on the command flags in order
	for this code snipped to work.

	Currently only the aboved specified formats are supported but developers can
	add support for other input sources by implementing the
	altsrc.InputSourceContext for their given sources.

	Here is a more complete sample of a command using YAML support:

	<!-- {
	"args": ["test-cmd", "--help"],
	"output": "&#45-test value.*default: 0"
	} -->
	``` go
	package notmain

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	"github.com/urfave/cli/altsrc"
	)

	func main() {
	app := cli.NewApp()

	flags := []cli.Flag{
	altsrc.NewIntFlag(cli.IntFlag{Name: "test"}),
	cli.StringFlag{Name: "load"},
	}

	app.Action = func(c *cli.Context) error {
	fmt.Println("yaml ist rad")
	return nil
	}

	app.Before = altsrc.InitInputSourceWithContext(flags, altsrc.NewYamlSourceFromFlagFunc("load"))
	app.Flags = flags

	app.Run(os.Args)
	}
	```

	### Subcommands

	Subcommands can be defined for a more git-like command line app.

	<!-- {
	"args": ["template", "add"],
	"output": "new task template: .+"
	} -->
	```go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Commands = []cli.Command{
	{
	Name: "add",
	Aliases: []string{"a"},
	Usage: "add a task to the list",
	Action: func(c *cli.Context) error {
	fmt.Println("added task: ", c.Args().First())
	return nil
	},
	},
	{
	Name: "complete",
	Aliases: []string{"c"},
	Usage: "complete a task on the list",
	Action: func(c *cli.Context) error {
	fmt.Println("completed task: ", c.Args().First())
	return nil
	},
	},
	{
	Name: "template",
	Aliases: []string{"t"},
	Usage: "options for task templates",
	Subcommands: []cli.Command{
	{
	Name: "add",
	Usage: "add a new template",
	Action: func(c *cli.Context) error {
	fmt.Println("new task template: ", c.Args().First())
	return nil
	},
	},
	{
	Name: "remove",
	Usage: "remove an existing template",
	Action: func(c *cli.Context) error {
	fmt.Println("removed task template: ", c.Args().First())
	return nil
	},
	},
	},
	},
	}

	app.Run(os.Args)
	}
	```

	### Subcommands categories

	For additional organization in apps that have many subcommands, you can
	associate a category for each command to group them together in the help
	output.

	E.g.

	```go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()

	app.Commands = []cli.Command{
	{
	Name: "noop",
	},
	{
	Name: "add",
	Category: "template",
	},
	{
	Name: "remove",
	Category: "template",
	},
	}

	app.Run(os.Args)
	}
	```

	Will include:

	```
	COMMANDS:
	noop

	Template actions:
	add
	remove
	```

	### Exit code

	Calling `App.Run` will not automatically call `os.Exit`, which means that by
	default the exit code will "fall through" to being `0`. An explicit exit code
	may be set by returning a non-nil error that fulfills `cli.ExitCoder`, or a
	`cli.MultiError` that includes an error that fulfills `cli.ExitCoder`, e.g.:

	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	app := cli.NewApp()
	app.Flags = []cli.Flag{
	cli.BoolTFlag{
	Name: "ginger-crouton",
	Usage: "is it in the soup?",
	},
	}
	app.Action = func(ctx *cli.Context) error {
	if !ctx.Bool("ginger-crouton") {
	return cli.NewExitError("it is not in the soup", 86)
	}
	return nil
	}

	app.Run(os.Args)
	}
	```

	### Bash Completion

	You can enable completion commands by setting the `EnableBashCompletion`
	flag on the `App` object. By default, this setting will only auto-complete to
	show an app's subcommands, but you can write your own completion methods for
	the App or its subcommands.

	<!-- {
	"args": ["complete", "--generate-bash-completion"],
	"output": "laundry"
	} -->
	``` go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	tasks := []string{"cook", "clean", "laundry", "eat", "sleep", "code"}

	app := cli.NewApp()
	app.EnableBashCompletion = true
	app.Commands = []cli.Command{
	{
	Name: "complete",
	Aliases: []string{"c"},
	Usage: "complete a task on the list",
	Action: func(c *cli.Context) error {
	fmt.Println("completed task: ", c.Args().First())
	return nil
	},
	BashComplete: func(c *cli.Context) {
	// This will complete if no args are passed
	if c.NArg() > 0 {
	return
	}
	for _, t := range tasks {
	fmt.Println(t)
	}
	},
	},
	}

	app.Run(os.Args)
	}
	```

	#### Enabling

	Source the `autocomplete/bash_autocomplete` file in your `.bashrc` file while
	setting the `PROG` variable to the name of your program:

	`PROG=myprogram source /.../cli/autocomplete/bash_autocomplete`

	#### Distribution

	Copy `autocomplete/bash_autocomplete` into `/etc/bash_completion.d/` and rename
	it to the name of the program you wish to add autocomplete support for (or
	automatically install it there if you are distributing a package). Don't forget
	to source the file to make it active in the current shell.

	```
	sudo cp src/bash_autocomplete /etc/bash_completion.d/<myprogram>
	source /etc/bash_completion.d/<myprogram>
	```

	Alternatively, you can just document that users should source the generic
	`autocomplete/bash_autocomplete` in their bash configuration with `$PROG` set
	to the name of their program (as above).

	#### Customization

	The default bash completion flag (`--generate-bash-completion`) is defined as
	`cli.BashCompletionFlag`, and may be redefined if desired, e.g.:

	<!-- {
	"args": ["--compgen"],
	"output": "wat\nhelp\nh"
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	cli.BashCompletionFlag = cli.BoolFlag{
	Name: "compgen",
	Hidden: true,
	}

	app := cli.NewApp()
	app.EnableBashCompletion = true
	app.Commands = []cli.Command{
	{
	Name: "wat",
	},
	}
	app.Run(os.Args)
	}
	```

	### Generated Help Text

	The default help flag (`-h/--help`) is defined as `cli.HelpFlag` and is checked
	by the cli internals in order to print generated help text for the app, command,
	or subcommand, and break execution.

	#### Customization

	All of the help text generation may be customized, and at multiple levels. The
	templates are exposed as variables `AppHelpTemplate`, `CommandHelpTemplate`, and
	`SubcommandHelpTemplate` which may be reassigned or augmented, and full override
	is possible by assigning a compatible func to the `cli.HelpPrinter` variable,
	e.g.:

	<!-- {
	"output": "Ha HA. I pwnd the help!!1"
	} -->
	``` go
	package main

	import (
	"fmt"
	"io"
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	// EXAMPLE: Append to an existing template
	cli.AppHelpTemplate = fmt.Sprintf(`%s

	WEBSITE: http://awesometown.example.com

	SUPPORT: support@awesometown.example.com

	`, cli.AppHelpTemplate)

	// EXAMPLE: Override a template
	cli.AppHelpTemplate = `NAME:
	{{.Name}} - {{.Usage}}
	USAGE:
	{{.HelpName}} {{if .VisibleFlags}}[global options]{{end}}{{if .Commands}} command [command options]{{end}} {{if .ArgsUsage}}{{.ArgsUsage}}{{else}}[arguments...]{{end}}
	{{if len .Authors}}
	AUTHOR:
	{{range .Authors}}{{ . }}{{end}}
	{{end}}{{if .Commands}}
	COMMANDS:
	{{range .Commands}}{{if not .HideHelp}} {{join .Names ", "}}{{ "\t"}}{{.Usage}}{{ "\n" }}{{end}}{{end}}{{end}}{{if .VisibleFlags}}
	GLOBAL OPTIONS:
	{{range .VisibleFlags}}{{.}}
	{{end}}{{end}}{{if .Copyright }}
	COPYRIGHT:
	{{.Copyright}}
	{{end}}{{if .Version}}
	VERSION:
	{{.Version}}
	{{end}}
	`

	// EXAMPLE: Replace the `HelpPrinter` func
	cli.HelpPrinter = func(w io.Writer, templ string, data interface{}) {
	fmt.Println("Ha HA. I pwnd the help!!1")
	}

	cli.NewApp().Run(os.Args)
	}
	```

	The default flag may be customized to something other than `-h/--help` by
	setting `cli.HelpFlag`, e.g.:

	<!-- {
	"args": ["-&#45halp"],
	"output": "haaaaalp.*HALP"
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	cli.HelpFlag = cli.BoolFlag{
	Name: "halp, haaaaalp",
	Usage: "HALP",
	EnvVar: "SHOW_HALP,HALPPLZ",
	}

	cli.NewApp().Run(os.Args)
	}
	```

	### Version Flag

	The default version flag (`-v/--version`) is defined as `cli.VersionFlag`, which
	is checked by the cli internals in order to print the `App.Version` via
	`cli.VersionPrinter` and break execution.

	#### Customization

	The default flag may be customized to something other than `-v/--version` by
	setting `cli.VersionFlag`, e.g.:

	<!-- {
	"args": ["-&#45print-version"],
	"output": "partay version 19\\.99\\.0"
	} -->
	``` go
	package main

	import (
	"os"

	"github.com/urfave/cli"
	)

	func main() {
	cli.VersionFlag = cli.BoolFlag{
	Name: "print-version, V",
	Usage: "print only the version",
	}

	app := cli.NewApp()
	app.Name = "partay"
	app.Version = "19.99.0"
	app.Run(os.Args)
	}
	```

	Alternatively, the version printer at `cli.VersionPrinter` may be overridden, e.g.:

	<!-- {
	"args": ["-&#45version"],
	"output": "version=19\\.99\\.0 revision=fafafaf"
	} -->
	``` go
	package main

	import (
	"fmt"
	"os"

	"github.com/urfave/cli"
	)

	var (
	Revision = "fafafaf"
	)

	func main() {
	cli.VersionPrinter = func(c *cli.Context) {
	fmt.Printf("version=%s revision=%s\n", c.App.Version, Revision)
	}

	app := cli.NewApp()
	app.Name = "partay"
	app.Version = "19.99.0"
	app.Run(os.Args)
	}
	```

	#### Full API Example

	Notice: This is a contrived (functioning) example meant strictly for API
	demonstration purposes. Use of one's imagination is encouraged.

	<!-- {
	"output": "made it!\nPhew!"
	} -->
	``` go
	package main

	import (
	"errors"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"time"

	"github.com/urfave/cli"
	)

	func init() {
	cli.AppHelpTemplate += "\nCUSTOMIZED: you bet ur muffins\n"
	cli.CommandHelpTemplate += "\nYMMV\n"
	cli.SubcommandHelpTemplate += "\nor something\n"

	cli.HelpFlag = cli.BoolFlag{Name: "halp"}
	cli.BashCompletionFlag = cli.BoolFlag{Name: "compgen", Hidden: true}
	cli.VersionFlag = cli.BoolFlag{Name: "print-version, V"}

	cli.HelpPrinter = func(w io.Writer, templ string, data interface{}) {
	fmt.Fprintf(w, "best of luck to you\n")
	}
	cli.VersionPrinter = func(c *cli.Context) {
	fmt.Fprintf(c.App.Writer, "version=%s\n", c.App.Version)
	}
	cli.OsExiter = func(c int) {
	fmt.Fprintf(cli.ErrWriter, "refusing to exit %d\n", c)
	}
	cli.ErrWriter = ioutil.Discard
	cli.FlagStringer = func(fl cli.Flag) string {
	return fmt.Sprintf("\t\t%s", fl.GetName())
	}
	}

	type hexWriter struct{}

	func (w *hexWriter) Write(p []byte) (int, error) {
	for _, b := range p {
	fmt.Printf("%x", b)
	}
	fmt.Printf("\n")

	return len(p), nil
	}

	type genericType struct{
	s string
	}

	func (g *genericType) Set(value string) error {
	g.s = value
	return nil
	}

	func (g *genericType) String() string {
	return g.s
	}

	func main() {
	app := cli.NewApp()
	app.Name = "kənˈtrīv"
	app.Version = "19.99.0"
	app.Compiled = time.Now()
	app.Authors = []cli.Author{
	cli.Author{
	Name: "Example Human",
	Email: "human@example.com",
	},
	}
	app.Copyright = "(c) 1999 Serious Enterprise"
	app.HelpName = "contrive"
	app.Usage = "demonstrate available API"
	app.UsageText = "contrive - demonstrating the available API"
	app.ArgsUsage = "[args and such]"
	app.Commands = []cli.Command{
	cli.Command{
	Name: "doo",
	Aliases: []string{"do"},
	Category: "motion",
	Usage: "do the doo",
	UsageText: "doo - does the dooing",
	Description: "no really, there is a lot of dooing to be done",
	ArgsUsage: "[arrgh]",
	Flags: []cli.Flag{
	cli.BoolFlag{Name: "forever, forevvarr"},
	},
	Subcommands: cli.Commands{
	cli.Command{
	Name: "wop",
	Action: wopAction,
	},
	},
	SkipFlagParsing: false,
	HideHelp: false,
	Hidden: false,
	HelpName: "doo!",
	BashComplete: func(c *cli.Context) {
	fmt.Fprintf(c.App.Writer, "--better\n")
	},
	Before: func(c *cli.Context) error {
	fmt.Fprintf(c.App.Writer, "brace for impact\n")
	return nil
	},
	After: func(c *cli.Context) error {
	fmt.Fprintf(c.App.Writer, "did we lose anyone?\n")
	return nil
	},
	Action: func(c *cli.Context) error {
	c.Command.FullName()
	c.Command.HasName("wop")
	c.Command.Names()
	c.Command.VisibleFlags()
	fmt.Fprintf(c.App.Writer, "dodododododoodododddooooododododooo\n")
	if c.Bool("forever") {
	c.Command.Run(c)
	}
	return nil
	},
	OnUsageError: func(c *cli.Context, err error, isSubcommand bool) error {
	fmt.Fprintf(c.App.Writer, "for shame\n")
	return err
	},
	},
	}
	app.Flags = []cli.Flag{
	cli.BoolFlag{Name: "fancy"},
	cli.BoolTFlag{Name: "fancier"},
	cli.DurationFlag{Name: "howlong, H", Value: time.Second * 3},
	cli.Float64Flag{Name: "howmuch"},
	cli.GenericFlag{Name: "wat", Value: &genericType{}},
	cli.Int64Flag{Name: "longdistance"},
	cli.Int64SliceFlag{Name: "intervals"},
	cli.IntFlag{Name: "distance"},
	cli.IntSliceFlag{Name: "times"},
	cli.StringFlag{Name: "dance-move, d"},
	cli.StringSliceFlag{Name: "names, N"},
	cli.UintFlag{Name: "age"},
	cli.Uint64Flag{Name: "bigage"},
	}
	app.EnableBashCompletion = true
	app.HideHelp = false
	app.HideVersion = false
	app.BashComplete = func(c *cli.Context) {
	fmt.Fprintf(c.App.Writer, "lipstick\nkiss\nme\nlipstick\nringo\n")
	}
	app.Before = func(c *cli.Context) error {
	fmt.Fprintf(c.App.Writer, "HEEEERE GOES\n")
	return nil
	}
	app.After = func(c *cli.Context) error {
	fmt.Fprintf(c.App.Writer, "Phew!\n")
	return nil
	}
	app.CommandNotFound = func(c *cli.Context, command string) {
	fmt.Fprintf(c.App.Writer, "Thar be no %q here.\n", command)
	}
	app.OnUsageError = func(c *cli.Context, err error, isSubcommand bool) error {
	if isSubcommand {
	return err
	}

	fmt.Fprintf(c.App.Writer, "WRONG: %#v\n", err)
	return nil
	}
	app.Action = func(c *cli.Context) error {
	cli.DefaultAppComplete(c)
	cli.HandleExitCoder(errors.New("not an exit coder, though"))
	cli.ShowAppHelp(c)
	cli.ShowCommandCompletions(c, "nope")
	cli.ShowCommandHelp(c, "also-nope")
	cli.ShowCompletions(c)
	cli.ShowSubcommandHelp(c)
	cli.ShowVersion(c)

	categories := c.App.Categories()
	categories.AddCommand("sounds", cli.Command{
	Name: "bloop",
	})

	for _, category := range c.App.Categories() {
	fmt.Fprintf(c.App.Writer, "%s\n", category.Name)
	fmt.Fprintf(c.App.Writer, "%#v\n", category.Commands)
	fmt.Fprintf(c.App.Writer, "%#v\n", category.VisibleCommands())
	}

	fmt.Printf("%#v\n", c.App.Command("doo"))
	if c.Bool("infinite") {
	c.App.Run([]string{"app", "doo", "wop"})
	}

	if c.Bool("forevar") {
	c.App.RunAsSubcommand(c)
	}
	c.App.Setup()
	fmt.Printf("%#v\n", c.App.VisibleCategories())
	fmt.Printf("%#v\n", c.App.VisibleCommands())
	fmt.Printf("%#v\n", c.App.VisibleFlags())

	fmt.Printf("%#v\n", c.Args().First())
	if len(c.Args()) > 0 {
	fmt.Printf("%#v\n", c.Args()[1])
	}
	fmt.Printf("%#v\n", c.Args().Present())
	fmt.Printf("%#v\n", c.Args().Tail())

	set := flag.NewFlagSet("contrive", 0)
	nc := cli.NewContext(c.App, set, c)

	fmt.Printf("%#v\n", nc.Args())
	fmt.Printf("%#v\n", nc.Bool("nope"))
	fmt.Printf("%#v\n", nc.BoolT("nerp"))
	fmt.Printf("%#v\n", nc.Duration("howlong"))
	fmt.Printf("%#v\n", nc.Float64("hay"))
	fmt.Printf("%#v\n", nc.Generic("bloop"))
	fmt.Printf("%#v\n", nc.Int64("bonk"))
	fmt.Printf("%#v\n", nc.Int64Slice("burnks"))
	fmt.Printf("%#v\n", nc.Int("bips"))
	fmt.Printf("%#v\n", nc.IntSlice("blups"))
	fmt.Printf("%#v\n", nc.String("snurt"))
	fmt.Printf("%#v\n", nc.StringSlice("snurkles"))
	fmt.Printf("%#v\n", nc.Uint("flub"))
	fmt.Printf("%#v\n", nc.Uint64("florb"))
	fmt.Printf("%#v\n", nc.GlobalBool("global-nope"))
	fmt.Printf("%#v\n", nc.GlobalBoolT("global-nerp"))
	fmt.Printf("%#v\n", nc.GlobalDuration("global-howlong"))
	fmt.Printf("%#v\n", nc.GlobalFloat64("global-hay"))
	fmt.Printf("%#v\n", nc.GlobalGeneric("global-bloop"))
	fmt.Printf("%#v\n", nc.GlobalInt("global-bips"))
	fmt.Printf("%#v\n", nc.GlobalIntSlice("global-blups"))
	fmt.Printf("%#v\n", nc.GlobalString("global-snurt"))
	fmt.Printf("%#v\n", nc.GlobalStringSlice("global-snurkles"))

	fmt.Printf("%#v\n", nc.FlagNames())
	fmt.Printf("%#v\n", nc.GlobalFlagNames())
	fmt.Printf("%#v\n", nc.GlobalIsSet("wat"))
	fmt.Printf("%#v\n", nc.GlobalSet("wat", "nope"))
	fmt.Printf("%#v\n", nc.NArg())
	fmt.Printf("%#v\n", nc.NumFlags())
	fmt.Printf("%#v\n", nc.Parent())

	nc.Set("wat", "also-nope")

	ec := cli.NewExitError("ohwell", 86)
	fmt.Fprintf(c.App.Writer, "%d", ec.ExitCode())
	fmt.Printf("made it!\n")
	return ec
	}

	if os.Getenv("HEXY") != "" {
	app.Writer = &hexWriter{}
	app.ErrWriter = &hexWriter{}
	}

	app.Metadata = map[string]interface{}{
	"layers": "many",
	"explicable": false,
	"whatever-values": 19.99,
	}

	app.Run(os.Args)
	}

	func wopAction(c *cli.Context) error {
	fmt.Fprintf(c.App.Writer, ":wave: over here, eh\n")
	return nil
	}
	```

	## Contribution Guidelines

	Feel free to put up a pull request to fix a bug or maybe add a feature. I will
	give it a code review and make sure that it does not break backwards
	compatibility. If I or any other collaborators agree that it is in line with
	the vision of the project, we will work with you to get the code into
	a mergeable state and merge it into the master branch.

	If you have contributed something significant to the project, we will most
	likely add you as a collaborator. As a collaborator you are given the ability
	to merge others pull requests. It is very important that new code does not
	break existing code, so be careful about what code you do choose to merge.

	If you feel like you have contributed to the project but have not yet been
	added as a collaborator, we probably forgot to add you, please open an issue.

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