cli

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cli.go

cli.go is 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.

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.go comes into play. cli.go makes command line programming fun, organized, and expressive!

Installation

Make sure you have a working Go environment (go 1.1+ is required). See the install instructions.

To install cli.go, simply run:

$ go get github.com/codegangsta/cli

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

export PATH=$PATH:$GOPATH/bin

Getting Started

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

package main

import (
  "os"
  "github.com/codegangsta/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:

package main

import (
  "os"
  "github.com/codegangsta/cli"
)

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

Example

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:

package main

import (
  "os"
  "github.com/codegangsta/cli"
)

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

  app.Run(os.Args)
}

Install our command to the $GOPATH/bin directory:

$ go install

Finally run our new command:

$ greet
Hello friend!

cli.go 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.

...
app.Action = func(c *cli.Context) {
  println("Hello", c.Args()[0])
}
...
Flags

Setting and querying flags is simple.

...
app.Flags = []cli.Flag {
  cli.StringFlag{
    Name: "lang",
    Value: "english",
    Usage: "language for the greeting",
  },
}
app.Action = func(c *cli.Context) {
  name := "someone"
  if len(c.Args()) > 0 {
    name = c.Args()[0]
  }
  if c.String("lang") == "spanish" {
    println("Hola", name)
  } else {
    println("Hello", name)
  }
}
...

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

...
var language string
app.Flags = []cli.Flag {
  cli.StringFlag{
    Name:        "lang",
    Value:       "english",
    Usage:       "language for the greeting",
    Destination: &language,
  },
}
app.Action = func(c *cli.Context) {
  name := "someone"
  if len(c.Args()) > 0 {
    name = c.Args()[0]
  }
  if language == "spanish" {
    println("Hola", name)
  } else {
    println("Hello", name)
  }
}
...

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

Alternate Names

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

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

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.

Values from the Environment

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

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

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

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

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

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

...
var 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) {
       println("completed task: ", c.Args().First())
    },
    BashComplete: func(c *cli.Context) {
      // This will complete if no args are passed
      if len(c.Args()) > 0 {
        return
      }
      for _, t := range tasks {
        fmt.Println(t)
      }
    },
  }
}
...
To Enable

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

To Distribute

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).

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, I 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 have any questions feel free to link @codegangsta to the issue in question and we can review it together.

If you feel like you have contributed to the project but have not yet been added as a collaborator, I probably forgot to add you. Hit @codegangsta up over email and we will get it figured out.

Documentation

Overview

Package cli provides a minimal framework for creating and organizing command line Go applications. cli is designed to be easy to understand and write, the most simple cli application can be written as follows: 

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

Of course this application does not do much, so let's make this an actual application: 

func main() {
  app := cli.NewApp()
  app.Name = "greet"
  app.Usage = "say a greeting"
  app.Action = func(c *cli.Context) {
    println("Greetings")
  }

  app.Run(os.Args)
}

Index

Constants

This section is empty.

Variables

View Source 
var AppHelpTemplate = `` /* 573-byte string literal not displayed */

The text template for the Default help topic. cli.go uses text/template to render templates. You can render custom help text by setting this variable.

View Source 
var BashCompletionFlag = BoolFlag{
	Name: "generate-bash-completion",
}

This flag enables bash-completion for all commands and subcommands

View Source 
var CommandHelpTemplate = `` /* 288-byte string literal not displayed */

The text template for the command help topic. cli.go uses text/template to render templates. You can render custom help text by setting this variable.

View Source 
var HelpFlag = BoolFlag{
	Name:  "help, h",
	Usage: "show help",
}

This flag prints the help for all commands and subcommands Set to the zero value (BoolFlag{}) to disable flag -- keeps subcommand unless HideHelp is set to true)

View Source 
var HelpPrinter helpPrinter = printHelp
View Source 
var SubcommandHelpTemplate = `` /* 318-byte string literal not displayed */

The text template for the subcommand help topic. cli.go uses text/template to render templates. You can render custom help text by setting this variable.

View Source 
var VersionFlag = BoolFlag{
	Name:  "version, v",
	Usage: "print the version",
}

This flag prints the version for the application

View Source 
var VersionPrinter = printVersion

Prints version for the App

Functions

func DefaultAppComplete 

func DefaultAppComplete(c *Context)

Prints the list of subcommands as the default app completion method

func ShowAppHelp 

func ShowAppHelp(c *Context)

func ShowCommandCompletions 

func ShowCommandCompletions(ctx *Context, command string)

Prints the custom completions for a given command

func ShowCommandHelp 

func ShowCommandHelp(ctx *Context, command string)

Prints help for the given command

func ShowCompletions 

func ShowCompletions(c *Context)

Prints the lists of commands within a given context

func ShowSubcommandHelp 

func ShowSubcommandHelp(c *Context)

Prints help for the given subcommand

func ShowVersion 

func ShowVersion(c *Context)

Prints the version number of the App

Types

type App 

type App struct {
	// The name of the program. Defaults to os.Args[0]
	Name string
	// Full name of command for help, defaults to Name
	HelpName string
	// Description of the program.
	Usage string
	// Description of the program argument format.
	ArgsUsage string
	// Version of the program
	Version string
	// List of commands to execute
	Commands []Command
	// List of flags to parse
	Flags []Flag
	// Boolean to enable bash completion commands
	EnableBashCompletion bool
	// Boolean to hide built-in help command
	HideHelp bool
	// Boolean to hide built-in version flag
	HideVersion bool
	// An action to execute when the bash-completion flag is set
	BashComplete func(context *Context)
	// An action to execute before any subcommands are run, but after the context is ready
	// If a non-nil error is returned, no subcommands are run
	Before func(context *Context) error
	// An action to execute after any subcommands are run, but after the subcommand has finished
	// It is run even if Action() panics
	After func(context *Context) error
	// The action to execute when no subcommands are specified
	Action func(context *Context)
	// Execute this function if the proper command cannot be found
	CommandNotFound func(context *Context, command string)
	// Compilation date
	Compiled time.Time
	// List of all authors who contributed
	Authors []Author
	// Copyright of the binary if any
	Copyright string
	// Name of Author (Note: Use App.Authors, this is deprecated)
	Author string
	// Email of Author (Note: Use App.Authors, this is deprecated)
	Email string
	// Writer writer to write output to
	Writer io.Writer
}

App is the main structure of a cli application. It is recomended that an app be created with the cli.NewApp() function

func NewApp 

func NewApp() *App

Creates a new cli Application with some reasonable defaults for Name, Usage, Version and Action.

func (*App) Command 

func (a *App) Command(name string) *Command

Returns the named command on App. Returns nil if the command does not exist

func (*App) Run 

func (a *App) Run(arguments []string) (err error)

Entry point to the cli app. Parses the arguments slice and routes to the proper flag/args combination

func (*App) RunAndExitOnError 

func (a *App) RunAndExitOnError()

Another entry point to the cli app, takes care of passing arguments and error handling

func (*App) RunAsSubcommand 

func (a *App) RunAsSubcommand(ctx *Context) (err error)

Invokes the subcommand given the context, parses ctx.Args() to generate command-specific flags

type Args 

type Args []string

func (Args) First 

func (a Args) First() string

Returns the first argument, or else a blank string

func (Args) Get 

func (a Args) Get(n int) string

Returns the nth argument, or else a blank string

func (Args) Present 

func (a Args) Present() bool

Checks if there are any arguments present

func (Args) Swap 

func (a Args) Swap(from, to int) error

Swaps arguments at the given indexes

func (Args) Tail 

func (a Args) Tail() []string

Return the rest of the arguments (not the first one) or else an empty string slice

type Author 

type Author struct {
	Name  string // The Authors name
	Email string // The Authors email
}

Author represents someone who has contributed to a cli project.

func (Author) String 

func (a Author) String() string

String makes Author comply to the Stringer interface, to allow an easy print in the templating process

type BoolFlag 

type BoolFlag struct {
	Name        string
	Usage       string
	EnvVar      string
	Destination *bool
}

BoolFlag is a switch that defaults to false

func (BoolFlag) Apply 

func (f BoolFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (BoolFlag) String 

func (f BoolFlag) String() string

String returns a readable representation of this value (for usage defaults)

type BoolTFlag 

type BoolTFlag struct {
	Name        string
	Usage       string
	EnvVar      string
	Destination *bool
}

BoolTFlag this represents a boolean flag that is true by default, but can still be set to false by --some-flag=false

func (BoolTFlag) Apply 

func (f BoolTFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (BoolTFlag) String 

func (f BoolTFlag) String() string

String returns a readable representation of this value (for usage defaults)

type Command 

type Command struct {
	// The name of the command
	Name string
	// short name of the command. Typically one character (deprecated, use `Aliases`)
	ShortName string
	// A list of aliases for the command
	Aliases []string
	// A short description of the usage of this command
	Usage string
	// A longer explanation of how the command works
	Description string
	// A short description of the arguments of this command
	ArgsUsage string
	// The function to call when checking for bash command completions
	BashComplete func(context *Context)
	// An action to execute before any sub-subcommands are run, but after the context is ready
	// If a non-nil error is returned, no sub-subcommands are run
	Before func(context *Context) error
	// An action to execute after any subcommands are run, but after the subcommand has finished
	// It is run even if Action() panics
	After func(context *Context) error
	// The function to call when this command is invoked
	Action func(context *Context)
	// List of child commands
	Subcommands []Command
	// List of flags to parse
	Flags []Flag
	// Treat all flags as normal arguments if true
	SkipFlagParsing bool
	// Boolean to hide built-in help command
	HideHelp bool

	// Full name of command for help, defaults to full command name, including parent commands.
	HelpName string
	// contains filtered or unexported fields
}

Command is a subcommand for a cli.App.

func (Command) FullName 

func (c Command) FullName() string

Returns the full name of the command. For subcommands this ensures that parent commands are part of the command path

func (Command) HasName 

func (c Command) HasName(name string) bool

Returns true if Command.Name or Command.ShortName matches given name

func (Command) Names 

func (c Command) Names() []string

func (Command) Run 

func (c Command) Run(ctx *Context) error

Invokes the command given the context, parses ctx.Args() to generate command-specific flags

type Context 

type Context struct {
	App     *App
	Command Command
	// contains filtered or unexported fields
}

Context is a type that is passed through to each Handler action in a cli application. Context can be used to retrieve context-specific Args and parsed command-line options.

func NewContext 

func NewContext(app *App, set *flag.FlagSet, parentCtx *Context) *Context

Creates a new context. For use in when invoking an App or Command action.

func (*Context) Args 

func (c *Context) Args() Args

Returns the command line arguments associated with the context.

func (*Context) Bool 

func (c *Context) Bool(name string) bool

Looks up the value of a local bool flag, returns false if no bool flag exists

func (*Context) BoolT 

func (c *Context) BoolT(name string) bool

Looks up the value of a local boolT flag, returns false if no bool flag exists

func (*Context) Duration 

func (c *Context) Duration(name string) time.Duration

Looks up the value of a local time.Duration flag, returns 0 if no time.Duration flag exists

func (*Context) FlagNames 

func (c *Context) FlagNames() (names []string)

Returns a slice of flag names used in this context.

func (*Context) Float64 

func (c *Context) Float64(name string) float64

Looks up the value of a local float64 flag, returns 0 if no float64 flag exists

func (*Context) Generic 

func (c *Context) Generic(name string) interface{}

Looks up the value of a local generic flag, returns nil if no generic flag exists

func (*Context) GlobalBool 

func (c *Context) GlobalBool(name string) bool

Looks up the value of a global bool flag, returns false if no bool flag exists

func (*Context) GlobalDuration 

func (c *Context) GlobalDuration(name string) time.Duration

Looks up the value of a global time.Duration flag, returns 0 if no time.Duration flag exists

func (*Context) GlobalFlagNames 

func (c *Context) GlobalFlagNames() (names []string)

Returns a slice of global flag names used by the app.

func (*Context) GlobalGeneric 

func (c *Context) GlobalGeneric(name string) interface{}

Looks up the value of a global generic flag, returns nil if no generic flag exists

func (*Context) GlobalInt 

func (c *Context) GlobalInt(name string) int

Looks up the value of a global int flag, returns 0 if no int flag exists

func (*Context) GlobalIntSlice 

func (c *Context) GlobalIntSlice(name string) []int

Looks up the value of a global int slice flag, returns nil if no int slice flag exists

func (*Context) GlobalIsSet 

func (c *Context) GlobalIsSet(name string) bool

Determines if the global flag was actually set

func (*Context) GlobalString 

func (c *Context) GlobalString(name string) string

Looks up the value of a global string flag, returns "" if no string flag exists

func (*Context) GlobalStringSlice 

func (c *Context) GlobalStringSlice(name string) []string

Looks up the value of a global string slice flag, returns nil if no string slice flag exists

func (*Context) Int 

func (c *Context) Int(name string) int

Looks up the value of a local int flag, returns 0 if no int flag exists

func (*Context) IntSlice 

func (c *Context) IntSlice(name string) []int

Looks up the value of a local int slice flag, returns nil if no int slice flag exists

func (*Context) IsSet 

func (c *Context) IsSet(name string) bool

Determines if the flag was actually set

func (*Context) NumFlags 

func (c *Context) NumFlags() int

Returns the number of flags set

func (*Context) Parent 

func (c *Context) Parent() *Context

Returns the parent context, if any

func (*Context) String 

func (c *Context) String(name string) string

Looks up the value of a local string flag, returns "" if no string flag exists

func (*Context) StringSlice 

func (c *Context) StringSlice(name string) []string

Looks up the value of a local string slice flag, returns nil if no string slice flag exists

type DurationFlag 

type DurationFlag struct {
	Name        string
	Value       time.Duration
	Usage       string
	EnvVar      string
	Destination *time.Duration
}

DurationFlag is a flag that takes a duration specified in Go's duration format: https://golang.org/pkg/time/#ParseDuration

func (DurationFlag) Apply 

func (f DurationFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (DurationFlag) String 

func (f DurationFlag) String() string

String returns a readable representation of this value (for usage defaults)

type Flag 

type Flag interface {
	fmt.Stringer
	// Apply Flag settings to the given flag set
	Apply(*flag.FlagSet)
	// contains filtered or unexported methods
}

Flag is a common interface related to parsing flags in cli. For more advanced flag parsing techniques, it is recomended that this interface be implemented.

type Float64Flag 

type Float64Flag struct {
	Name        string
	Value       float64
	Usage       string
	EnvVar      string
	Destination *float64
}

Float64Flag is a flag that takes an float value Errors if the value provided cannot be parsed

func (Float64Flag) Apply 

func (f Float64Flag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (Float64Flag) String 

func (f Float64Flag) String() string

String returns the usage

type Generic 

type Generic interface {
	Set(value string) error
	String() string
}

Generic is a generic parseable type identified by a specific flag

type GenericFlag 

type GenericFlag struct {
	Name   string
	Value  Generic
	Usage  string
	EnvVar string
}

GenericFlag is the flag type for types implementing Generic

func (GenericFlag) Apply 

func (f GenericFlag) Apply(set *flag.FlagSet)

Apply takes the flagset and calls Set on the generic flag with the value provided by the user for parsing by the flag

func (GenericFlag) String 

func (f GenericFlag) String() string

String returns the string representation of the generic flag to display the help text to the user (uses the String() method of the generic flag to show the value)

type IntFlag 

type IntFlag struct {
	Name        string
	Value       int
	Usage       string
	EnvVar      string
	Destination *int
}

IntFlag is a flag that takes an integer Errors if the value provided cannot be parsed

func (IntFlag) Apply 

func (f IntFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (IntFlag) String 

func (f IntFlag) String() string

String returns the usage

type IntSlice 

type IntSlice []int

StringSlice is an opaque type for []int to satisfy flag.Value

func (*IntSlice) Set 

func (f *IntSlice) Set(value string) error

Set parses the value into an integer and appends it to the list of values

func (*IntSlice) String 

func (f *IntSlice) String() string

String returns a readable representation of this value (for usage defaults)

func (*IntSlice) Value 

func (f *IntSlice) Value() []int

Value returns the slice of ints set by this flag

type IntSliceFlag 

type IntSliceFlag struct {
	Name   string
	Value  *IntSlice
	Usage  string
	EnvVar string
}

IntSliceFlag is an int flag that can be specified multiple times on the command-line

func (IntSliceFlag) Apply 

func (f IntSliceFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (IntSliceFlag) String 

func (f IntSliceFlag) String() string

String returns the usage

type MultiError 

type MultiError struct {
	Errors []error
}

func NewMultiError 

func NewMultiError(err ...error) MultiError

func (MultiError) Error 

func (m MultiError) Error() string

type StringFlag 

type StringFlag struct {
	Name        string
	Value       string
	Usage       string
	EnvVar      string
	Destination *string
}

StringFlag represents a flag that takes as string value

func (StringFlag) Apply 

func (f StringFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (StringFlag) String 

func (f StringFlag) String() string

String returns the usage

type StringSlice 

type StringSlice []string

StringSlice is an opaque type for []string to satisfy flag.Value

func (*StringSlice) Set 

func (f *StringSlice) Set(value string) error

Set appends the string value to the list of values

func (*StringSlice) String 

func (f *StringSlice) String() string

String returns a readable representation of this value (for usage defaults)

func (*StringSlice) Value 

func (f *StringSlice) Value() []string

Value returns the slice of strings set by this flag

type StringSliceFlag 

type StringSliceFlag struct {
	Name   string
	Value  *StringSlice
	Usage  string
	EnvVar string
}

StringSlice is a string flag that can be specified multiple times on the command-line

func (StringSliceFlag) Apply 

func (f StringSliceFlag) Apply(set *flag.FlagSet)

Apply populates the flag given the flag set and environment

func (StringSliceFlag) String 

func (f StringSliceFlag) String() string

String returns the usage

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