kingpin

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 Go to latest Published: Sep 3, 2019 License: Apache-2.0, MIT Imports: 24 Imported by: 0

README

Kingpin - A Go (golang) command line and flag parser Build Status

Overview

Kingpin is a fluent-style, type-safe command-line parser. It supports flags, nested commands, and positional arguments.

Install it with:

$ go get gopkg.in/alecthomas/kingpin.v2

It looks like this:

var (
  verbose = kingpin.Flag("verbose", "Verbose mode.").Short('v').Bool()
  name    = kingpin.Arg("name", "Name of user.").Required().String()
)

func main() {
  kingpin.Parse()
  fmt.Printf("%v, %s\n", *verbose, *name)
}

More examples are available.

Second to parsing, providing the user with useful help is probably the most important thing a command-line parser does. Kingpin tries to provide detailed contextual help if --help is encountered at any point in the command line (excluding after --).

Features

  • Help output that isn't as ugly as sin.
  • Fully customisable help, via Go templates.
  • Parsed, type-safe flags (kingpin.Flag("f", "help").Int())
  • Parsed, type-safe positional arguments (kingpin.Arg("a", "help").Int()).
  • Parsed, type-safe, arbitrarily deep commands (kingpin.Command("c", "help")).
  • Support for required flags and required positional arguments (kingpin.Flag("f", "").Required().Int()).
  • Support for arbitrarily nested default commands (command.Default()).
  • Callbacks per command, flag and argument (kingpin.Command("c", "").Action(myAction)).
  • POSIX-style short flag combining (-a -b -> -ab).
  • Short-flag+parameter combining (-a parm -> -aparm).
  • Read command-line from files (@<file>).
  • Automatically generate man pages (--help-man).

User-visible changes between v1 and v2

Flags can be used at any point after their definition.

Flags can be specified at any point after their definition, not just immediately after their associated command. From the chat example below, the following used to be required:

$ chat --server=chat.server.com:8080 post --image=~/Downloads/owls.jpg pics

But the following will now work:

$ chat post --server=chat.server.com:8080 --image=~/Downloads/owls.jpg pics
Short flags can be combined with their parameters

Previously, if a short flag was used, any argument to that flag would have to be separated by a space. That is no longer the case.

API changes between v1 and v2

  • ParseWithFileExpansion() is gone. The new parser directly supports expanding @<file>.
  • Added FatalUsage() and FatalUsageContext() for displaying an error + usage and terminating.
  • Dispatch() renamed to Action().
  • Added ParseContext() for parsing a command line into its intermediate context form without executing.
  • Added Terminate() function to override the termination function.
  • Added UsageForContextWithTemplate() for printing usage via a custom template.
  • Added UsageTemplate() for overriding the default template to use. Two templates are included:
    1. DefaultUsageTemplate - default template.
    2. CompactUsageTemplate - compact command template for larger applications.

Versions

Kingpin uses gopkg.in for versioning.

The current stable version is gopkg.in/alecthomas/kingpin.v2. The previous version, gopkg.in/alecthomas/kingpin.v1, is deprecated and in maintenance mode.

V2 is the current stable version

Installation:

$ go get gopkg.in/alecthomas/kingpin.v2
V1 is the OLD stable version

Installation:

$ go get gopkg.in/alecthomas/kingpin.v1

Change History

  • 2015-09-19 -- Stable v2.1.0 release.

    • Added command.Default() to specify a default command to use if no other command matches. This allows for convenient user shortcuts.
    • Exposed HelpFlag and VersionFlag for further customisation.
    • Action() and PreAction() added and both now support an arbitrary number of callbacks.
    • kingpin.SeparateOptionalFlagsUsageTemplate.
    • --help-long and --help-man (hidden by default) flags.
    • Flags are "interspersed" by default, but can be disabled with app.Interspersed(false).
    • Added flags for all simple builtin types (int8, uint16, etc.) and slice variants.
    • Use app.Writer(os.Writer) to specify the default writer for all output functions.
    • Dropped os.Writer prefix from all printf-like functions.

  • 2015-05-22 -- Stable v2.0.0 release.

    • Initial stable release of v2.0.0.
    • Fully supports interspersed flags, commands and arguments.
    • Flags can be present at any point after their logical definition.
    • Application.Parse() terminates if commands are present and a command is not parsed.
    • Dispatch() -> Action().
    • Actions are dispatched after all values are populated.
    • Override termination function (defaults to os.Exit).
    • Override output stream (defaults to os.Stderr).
    • Templatised usage help, with default and compact templates.
    • Make error/usage functions more consistent.
    • Support argument expansion from files by default (with @).
    • Fully public data model is available via .Model().
    • Parser has been completely refactored.
    • Parsing and execution has been split into distinct stages.
    • Use go generate to generate repeated flags.
    • Support combined short-flag+argument: -fARG.

  • 2015-01-23 -- Stable v1.3.4 release.

    • Support "--" for separating flags from positional arguments.
    • Support loading flags from files (ParseWithFileExpansion()). Use @FILE as an argument.
    • Add post-app and post-cmd validation hooks. This allows arbitrary validation to be added.
    • A bunch of improvements to help usage and formatting.
    • Support arbitrarily nested sub-commands.

  • 2014-07-08 -- Stable v1.2.0 release.

    • Pass any value through to Strings() when final argument. Allows for values that look like flags to be processed.
    • Allow --help to be used with commands.
    • Support Hidden() flags.
    • Parser for units.Base2Bytes type. Allows for flags like --ram=512MB or --ram=1GB.
    • Add an Enum() value, allowing only one of a set of values to be selected. eg. Flag(...).Enum("debug", "info", "warning").

  • 2014-06-27 -- Stable v1.1.0 release.

    • Bug fixes.
    • Always return an error (rather than panicing) when misconfigured.
    • OpenFile(flag, perm) value type added, for finer control over opening files.
    • Significantly improved usage formatting.

  • 2014-06-19 -- Stable v1.0.0 release.

    • Support cumulative positional arguments.
    • Return error rather than panic when there are fatal errors not caught by the type system. eg. when a default value is invalid.
    • Use gokpg.in.

  • 2014-06-10 -- Place-holder streamlining.

    • Renamed MetaVar to PlaceHolder.
    • Removed MetaVarFromDefault. Kingpin now uses heuristics to determine what to display.

Examples

Simple Example

Kingpin can be used for simple flag+arg applications like so:

$ ping --help
usage: ping [<flags>] <ip> [<count>]

Flags:
  --debug            Enable debug mode.
  --help             Show help.
  -t, --timeout=5s   Timeout waiting for ping.

Args:
  <ip>        IP address to ping.
  [<count>]   Number of packets to send
$ ping 1.2.3.4 5
Would ping: 1.2.3.4 with timeout 5s and count 0

From the following source:

package main

import (
  "fmt"

  "gopkg.in/alecthomas/kingpin.v2"
)

var (
  debug   = kingpin.Flag("debug", "Enable debug mode.").Bool()
  timeout = kingpin.Flag("timeout", "Timeout waiting for ping.").Default("5s").OverrideDefaultFromEnvar("PING_TIMEOUT").Short('t').Duration()
  ip      = kingpin.Arg("ip", "IP address to ping.").Required().IP()
  count   = kingpin.Arg("count", "Number of packets to send").Int()
)

func main() {
  kingpin.Version("0.0.1")
  kingpin.Parse()
  fmt.Printf("Would ping: %s with timeout %s and count %d", *ip, *timeout, *count)
}
Complex Example

Kingpin can also produce complex command-line applications with global flags, subcommands, and per-subcommand flags, like this:

$ chat --help
usage: chat [<flags>] <command> [<flags>] [<args> ...]

A command-line chat application.

Flags:
  --help              Show help.
  --debug             Enable debug mode.
  --server=127.0.0.1  Server address.

Commands:
  help [<command>]
    Show help for a command.

  register <nick> <name>
    Register a new user.

  post [<flags>] <channel> [<text>]
    Post a message to a channel.

$ chat help post
usage: chat [<flags>] post [<flags>] <channel> [<text>]

Post a message to a channel.

Flags:
  --image=IMAGE  Image to post.

Args:
  <channel>  Channel to post to.
  [<text>]   Text to post.

$ chat post --image=~/Downloads/owls.jpg pics
...

From this code:

package main

import (
  "os"
  "strings"
  "gopkg.in/alecthomas/kingpin.v2"
)

var (
  app      = kingpin.New("chat", "A command-line chat application.")
  debug    = app.Flag("debug", "Enable debug mode.").Bool()
  serverIP = app.Flag("server", "Server address.").Default("127.0.0.1").IP()

  register     = app.Command("register", "Register a new user.")
  registerNick = register.Arg("nick", "Nickname for user.").Required().String()
  registerName = register.Arg("name", "Name of user.").Required().String()

  post        = app.Command("post", "Post a message to a channel.")
  postImage   = post.Flag("image", "Image to post.").File()
  postChannel = post.Arg("channel", "Channel to post to.").Required().String()
  postText    = post.Arg("text", "Text to post.").Strings()
)

func main() {
  switch kingpin.MustParse(app.Parse(os.Args[1:])) {
  // Register user
  case register.FullCommand():
    println(*registerNick)

  // Post message
  case post.FullCommand():
    if *postImage != nil {
    }
    text := strings.Join(*postText, " ")
    println("Post:", text)
  }
}

Reference Documentation

Displaying errors and usage information

Kingpin exports a set of functions to provide consistent errors and usage information to the user.

Error messages look something like this:

<app>: error: <message>

The functions on Application are:

Function Purpose
Errorf(format, args) Display a printf formatted error to the user.
Fatalf(format, args) As with Errorf, but also call the termination handler.
FatalUsage(format, args) As with Fatalf, but also print contextual usage information.
FatalUsageContext(context, format, args) As with Fatalf, but also print contextual usage information from a ParseContext.
FatalIfError(err, format, args) Conditionally print an error prefixed with format+args, then call the termination handler

There are equivalent global functions in the kingpin namespace for the default kingpin.CommandLine instance.

Sub-commands

Kingpin supports nested sub-commands, with separate flag and positional arguments per sub-command. Note that positional arguments may only occur after sub-commands.

For example:

var (
  deleteCommand     = kingpin.Command("delete", "Delete an object.")
  deleteUserCommand = deleteCommand.Command("user", "Delete a user.")
  deleteUserUIDFlag = deleteUserCommand.Flag("uid", "Delete user by UID rather than username.")
  deleteUserUsername = deleteUserCommand.Arg("username", "Username to delete.")
  deletePostCommand = deleteCommand.Command("post", "Delete a post.")
)

func main() {
  switch kingpin.Parse() {
  case "delete user":
  case "delete post":
  }
}
Custom Parsers

Kingpin supports both flag and positional argument parsers for converting to Go types. For example, some included parsers are Int(), Float(), Duration() and ExistingFile().

Parsers conform to Go's flag.Value interface, so any existing implementations will work.

For example, a parser for accumulating HTTP header values might look like this:

type HTTPHeaderValue http.Header

func (h *HTTPHeaderValue) Set(value string) error {
  parts := strings.SplitN(value, ":", 2)
  if len(parts) != 2 {
    return fmt.Errorf("expected HEADER:VALUE got '%s'", value)
  }
  (*http.Header)(h).Add(parts[0], parts[1])
  return nil
}

func (h *HTTPHeaderValue) String() string {
  return ""
}

As a convenience, I would recommend something like this:

func HTTPHeader(s Settings) (target *http.Header) {
  target = &http.Header{}
  s.SetValue((*HTTPHeaderValue)(target))
  return
}

You would use it like so:

headers = HTTPHeader(kingpin.Flag("header", "Add a HTTP header to the request.").Short('H'))
Repeatable flags

Depending on the Value they hold, some flags may be repeated. The IsCumulative() bool function on Value tells if it's safe to call Set() multiple times or if an error should be raised if several values are passed.

The built-in Values returning slices and maps, as well as Counter are examples of Values that make a flag repeatable.

Boolean values

Boolean values are uniquely managed by Kingpin. Each boolean flag will have a negative complement: --<name> and --no-<name>.

Default Values

The default value is the zero value for a type. This can be overridden with the Default(value...) function on flags and arguments. This function accepts one or several strings, which are parsed by the value itself, so they must be compliant with the format expected.

Place-holders in Help

The place-holder value for a flag is the value used in the help to describe the value of a non-boolean flag.

The value provided to PlaceHolder() is used if provided, then the value provided by Default() if provided, then finally the capitalised flag name is used.

Here are some examples of flags with various permutations:

--name=NAME           // Flag(...).String()
--name="Harry"        // Flag(...).Default("Harry").String()
--name=FULL-NAME      // flag(...).PlaceHolder("FULL-NAME").Default("Harry").String()
Consuming all remaining arguments

A common command-line idiom is to use all remaining arguments for some purpose. eg. The following command accepts an arbitrary number of IP addresses as positional arguments:

./cmd ping 10.1.1.1 192.168.1.1

Such arguments are similar to repeatable flags, but for arguments. Therefore they use the same IsCumulative() bool function on the underlying Value, so the built-in Values for which the Set() function can be called several times will consume multiple arguments.

To implement the above example with a custom Value, we might do something like this:

type ipList []net.IP

func (i *ipList) Set(value string) error {
  if ip := net.ParseIP(value); ip == nil {
    return fmt.Errorf("'%s' is not an IP address", value)
  } else {
    *i = append(*i, ip)
    return nil
  }
}

func (i *ipList) String() string {
  return ""
}

func (i *ipList) IsCumulative() bool {
  return true
}

func IPList(s Settings) (target *[]net.IP) {
  target = new([]net.IP)
  s.SetValue((*ipList)(target))
  return
}

And use it like so:

ips := IPList(kingpin.Arg("ips", "IP addresses to ping."))
Struct tag interpolation

Kingpin v3 now supports defining flags, arguments and commands via struct reflection. If desired, this can (almost) completely replace the fluent-style interface.

The name of the flag will default to the CamelCase name transformed to camel- case. This can be overridden with the "long" tag.

All basic Go types are supported including floats, ints, strings, time.Duration, and slices of same.

For compatibility, also supports the tags used by https://github.com/jessevdk/go-flags

type MyFlags struct {
  Arg string `arg:"true" help:"An argument"`
  Debug bool `help:"Enable debug mode."`
  URL string `help:"URL to connect to." default:"localhost:80"`

  Login struct {
    Name string `help:"Username to authenticate with." args:"true"`
  } `help:"Login to server."`
}

flags := &MyFlags{}
kingpin.Struct(flags)

Supported struct tags are:

Tag Description
help Help text.
placeholder Placeholder text.
default Default value.
short Short name, if flag.
long Long name, for overriding field name.
required If present, flag/arg is required.
hidden If present, flag/arg/command is hidden.
enum For enums, a comma separated list of cases.
arg If true, field is an argument.
Bash/ZSH Shell Completion

By default, all flags and commands/subcommands generate completions internally.

Out of the box, CLI tools using kingpin should be able to take advantage of completion hinting for flags and commands. By specifying --completion-bash as the first argument, your CLI tool will show possible subcommands. By ending your argv with --, hints for flags will be shown.

To allow your end users to take advantage you must package a /etc/bash_completion.d script with your distribution (or the equivalent for your target platform/shell). An alternative is to instruct your end user to source a script from their bash_profile (or equivalent).

Fortunately Kingpin makes it easy to generate or source a script for use with end users shells. ./yourtool --completion-script-bash and ./yourtool --completion-script-zsh will generate these scripts for you.

Installation by Package

For the best user experience, you should bundle your pre-created completion script with your CLI tool and install it inside /etc/bash_completion.d (or equivalent). A good suggestion is to add this as an automated step to your build pipeline, in the implementation is improved for bug fixed.

Installation by bash_profile

Alternatively, instruct your users to add an additional statement to their bash_profile (or equivalent):

eval "$(your-cli-tool --completion-script-bash)"

Or for ZSH

eval "$(your-cli-tool --completion-script-zsh)"
Additional API

To provide more flexibility, a completion option API has been exposed for flags to allow user defined completion options, to extend completions further than just EnumVar/Enum.

Provide Static Options

When using an Enum or EnumVar, users are limited to only the options given. Maybe we wish to hint possible options to the user, but also allow them to provide their own custom option. HintOptions gives this functionality to flags.

app := kingpin.New("completion", "My application with bash completion.")
app.Flag("port", "Provide a port to connect to").
    Required().
    HintOptions("80", "443", "8080").
    IntVar(&c.port)

Provide Dynamic Options

Consider the case that you needed to read a local database or a file to provide suggestions. You can dynamically generate the options

func listHosts(args []string) []string {
  // Provide a dynamic list of hosts from a hosts file or otherwise
  // for bash completion. In this example we simply return static slice.

  // You could use this functionality to reach into a hosts file to provide
  // completion for a list of known hosts.
  return []string{"sshhost.example", "webhost.example", "ftphost.example"}
}

app := kingpin.New("completion", "My application with bash completion.")
app.Flag("flag-1", "").HintAction(listHosts).String()

EnumVar/Enum

When using Enum or EnumVar, any provided options will be automatically used for bash autocompletion. However, if you wish to provide a subset or different options, you can use HintOptions or HintAction which will override the default completion options for Enum/EnumVar.

Examples

You can see an in depth example of the completion API within examples/completion/main.go

Supporting -h for help

kingpin.CommandLine.GetFlag("help").Short('h')

Custom help

Kingpin supports templatised help using the text/template library.

You can specify the template to use with the Application.UsageTemplate() function.

There are four included templates: kingpin.DefaultUsageTemplate is the default, kingpin.CompactUsageTemplate provides a more compact representation for more complex command-line structures, and kingpin.ManPageTemplate is used to generate man pages.

See the above templates for examples of usage, and the the function UsageForContextWithTemplate() method for details on the context.

Adding a new help command

It is often useful to add extra help formats, such as man pages, etc. Here's how you'd add a --help-man flag:

kingpin.Flag("help-man", "Generate man page.").
  UsageActionTemplate(kingpin.ManPageTemplate).
  Bool()
Default help template
$ go run ./examples/curl/curl.go --help
usage: curl [<flags>] <command> [<args> ...]

An example implementation of curl.

Flags:
  --help            Show help.
  -t, --timeout=5s  Set connection timeout.
  -H, --headers=HEADER=VALUE
                    Add HTTP headers to the request.

Commands:
  help [<command>...]
    Show help.

  get url <url>
    Retrieve a URL.

  get file <file>
    Retrieve a file.

  post [<flags>] <url>
    POST a resource.
Compact help template
$ go run ./examples/curl/curl.go --help
usage: curl [<flags>] <command> [<args> ...]

An example implementation of curl.

Flags:
  --help            Show help.
  -t, --timeout=5s  Set connection timeout.
  -H, --headers=HEADER=VALUE
                    Add HTTP headers to the request.

Commands:
  help [<command>...]
  get [<flags>]
    url <url>
    file <file>
  post [<flags>] <url>

Documentation

Overview

Package kingpin provides command line interfaces like this: 

$ chat
usage: chat [<flags>] <command> [<flags>] [<args> ...]

Flags:
  --debug              enable debug mode
  --help               Show help.
  --server=127.0.0.1   server address

Commands:
  help <command>
    Show help for a command.

  post [<flags>] <channel>
    Post a message to a channel.

  register <nick> <name>
    Register a new user.

$ chat help post
usage: chat [<flags>] post [<flags>] <channel> [<text>]

Post a message to a channel.

Flags:
  --image=IMAGE   image to post

Args:
  <channel>   channel to post to
  [<text>]    text to post
$ chat post --image=~/Downloads/owls.jpg pics

From code like this: 

package main

import "gopkg.in/alecthomas/kingpin.v1"

var (
  debug    = kingpin.Flag("debug", "enable debug mode").Default("false").Bool()
  serverIP = kingpin.Flag("server", "server address").Default("127.0.0.1").IP()

  register     = kingpin.Command("register", "Register a new user.")
  registerNick = register.Arg("nick", "nickname for user").Required().String()
  registerName = register.Arg("name", "name of user").Required().String()

  post        = kingpin.Command("post", "Post a message to a channel.")
  postImage   = post.Flag("image", "image to post").ExistingFile()
  postChannel = post.Arg("channel", "channel to post to").Required().String()
  postText    = post.Arg("text", "text to post").String()
)

func main() {
  switch kingpin.Parse() {
  // Register user
  case "register":
    println(*registerNick)

  // Post message
  case "post":
    if *postImage != nil {
    }
    if *postText != "" {
    }
  }
}

nolint: golint

Index

Constants

This section is empty.

Variables

View Source 
var BashCompletionTemplate = `` /* 327-byte string literal not displayed */
View Source 
var (
	// CommandLine is the default Kingpin parser.
	CommandLine = New(filepath.Base(os.Args[0]), "")
)
View Source 
var CompactUsageTemplate = `` /* 1320-byte string literal not displayed */

CompactUsageTemplate is a template with compactly formatted commands for large command structures.

View Source 
var DefaultUsageTemplate = `` /* 996-byte string literal not displayed */

DefaultUsageTemplate is the default usage template.

View Source 
var ManPageTemplate = `` /* 890-byte string literal not displayed */
View Source 
var T = initI18N()

T is a translation function.

View Source 
var (
	TokenEOLMarker = Token{-1, TokenEOL, ""}
)
View Source 
var ZshCompletionTemplate = `` /* 470-byte string literal not displayed */

Functions

func Errorf 

func Errorf(format string, args ...interface{})

Errorf prints an error message to stderr.

func ExpandArgsFromFile 

func ExpandArgsFromFile(filename string) (out []string, err error)

Expand arguments from a file. Lines starting with # will be treated as comments.

func FatalIfError 

func FatalIfError(err error, format string, args ...interface{})

FatalIfError prints an error and exits if err is not nil. The error is printed with the given prefix.

func FatalUsage 

func FatalUsage(format string, args ...interface{})

FatalUsage prints an error message followed by usage information, then exits with a non-zero status.

func FatalUsageContext 

func FatalUsageContext(context *ParseContext, format string, args ...interface{})

FatalUsageContext writes a printf formatted error message to stderr, then usage information for the given ParseContext, before exiting.

func Fatalf 

func Fatalf(format string, args ...interface{})

Fatalf prints an error message to stderr and exits.

func MustParse 

func MustParse(command string, err error) string

MustParse can be used with app.Parse(args) to exit with an error if parsing fails.

func Parse 

func Parse() string

Parse and return the selected command. Will call the termination handler if an error is encountered.

func SetLanguage 

func SetLanguage(lang string, others ...string) error

SetLanguage sets the language for Kingpin.

func TError 

func TError(msg string, args ...interface{}) error

TError is an error that translates itself.

It has the same signature and usage as T().

func Usage 

func Usage()

Usage prints usage to stderr.

Types

type Action 

type Action func(app *Application, element *ParseElement, context *ParseContext) error

Action callback triggered during parsing.

"element" is the flag, argument or command associated with the callback. It contains the Clause and the string value.

"context" contains the full parse context, including all other elements that have been parsed.

type Application 

type Application struct {
	Name string
	Help string
	// contains filtered or unexported fields
}

An Application contains the definitions of flags, arguments and commands for an application.

func New 

func New(name, help string) *Application

New creates a new Kingpin application instance.

func Struct 

func Struct(v interface{}) *Application

Struct creates a command-line from a struct.

func UsageTemplate 

func UsageTemplate(template string) *Application

UsageTemplate associates a template with a flag. The flag must be a Bool() and must already be defined.

func Version 

func Version(version string) *Application

Version adds a flag for displaying the application version number.

func (*Application) Action 

func (a *Application) Action(action Action) *Application

Action is an application-wide callback. It is used in two situations: first, with a nil "element" parameter when parsing is complete, and second whenever a command, argument or flag is encountered.

func (*Application) Author 

func (a *Application) Author(author string) *Application

Author sets the author name for usage templates.

func (*Application) CmdCompletion 

func (c *Application) CmdCompletion(context *ParseContext) []string

CmdCompletion returns completion options for arguments, if that's where parsing left off, or commands if there aren't any unsatisfied args.

func (*Application) Command 

func (a *Application) Command(name, help string) *CmdClause

Command adds a new top-level command.

func (*Application) DefaultEnvars 

func (a *Application) DefaultEnvars() *Application

DefaultEnvars configures all flags (that do not already have an associated envar) to use a default environment variable in the form "<app>_<flag>".

For example, if the application is named "foo" and a flag is named "bar- waz" the environment variable: "FOO_BAR_WAZ".

func (*Application) Errorf 

func (a *Application) Errorf(format string, args ...interface{})

Errorf prints an error message to w in the format "<appname>: error: <message>".

func (*Application) FatalIfError 

func (a *Application) FatalIfError(err error, format string, args ...interface{})

FatalIfError prints an error and exits if err is not nil. The error is printed with the given formatted string, if any.

func (*Application) FatalUsage 

func (a *Application) FatalUsage(format string, args ...interface{})

FatalUsage prints an error message followed by usage information, then exits with a non-zero status.

func (*Application) FatalUsageContext 

func (a *Application) FatalUsageContext(context *ParseContext, format string, args ...interface{})

FatalUsageContext writes a printf formatted error message to w, then usage information for the given ParseContext, before exiting.

func (*Application) Fatalf 

func (a *Application) Fatalf(format string, args ...interface{})

Fatalf writes a formatted error to w then terminates with exit status 1.

func (*Application) FlagCompletion 

func (c *Application) FlagCompletion(flagName string, flagValue string) (choices []string, flagMatch bool, optionMatch bool)

func (*Application) Interspersed 

func (a *Application) Interspersed(interspersed bool) *Application

Interspersed control if flags can be interspersed with positional arguments

true (the default) means that they can, false means that all the flags must appear before the first positional arguments.

func (*Application) Model 

func (a *Application) Model() *ApplicationModel

func (*Application) Parse 

func (a *Application) Parse(args []string) (command string, err error)

Parse parses command-line arguments. It returns the selected command and an error. The selected command will be a space separated subcommand, if subcommands have been configured.

This will populate all flag and argument values, call all callbacks, and so on.

func (*Application) ParseContext 

func (a *Application) ParseContext(args []string) (*ParseContext, error)

ParseContext parses the given command line and returns the fully populated ParseContext.

func (*Application) PreAction 

func (a *Application) PreAction(action Action) *Application

PreAction is an application-wide callback. It is in two situations: first, with a nil "element" parameter, and second, whenever a command, argument or flag is encountered.

func (*Application) Struct 

func (a *Application) Struct(v interface{}) error

Struct allows applications to define flags with struct tags.

Supported struct tags are: help, placeholder, default, short, long, required, hidden, env, enum, and arg.

The name of the flag will default to the CamelCase name transformed to camel-case. This can be overridden with the "long" tag.

All basic Go types are supported including floats, ints, strings, time.Duration, and slices of same.

For compatibility, also supports the tags used by https://github.com/jessevdk/go-flags

func (*Application) Terminate 

func (a *Application) Terminate(terminate func(int)) *Application

Terminate specifies the termination handler. Defaults to os.Exit(status). If nil is passed, a no-op function will be used.

func (*Application) Usage 

func (a *Application) Usage(args []string)

Usage writes application usage to Writer. It parses args to determine appropriate help context, such as which command to show help for.

func (*Application) UsageContext 

func (a *Application) UsageContext(context *UsageContext) *Application

UsageContext specifies the UsageContext to use when displaying usage information via --help.

func (*Application) UsageForContext 

func (a *Application) UsageForContext(context *ParseContext) error

UsageForContext displays usage information from a ParseContext (obtained from Application.ParseContext() or Action(f) callbacks).

func (*Application) UsageForContextWithTemplate 

func (a *Application) UsageForContextWithTemplate(usageContext *UsageContext, parseContext *ParseContext) error

UsageForContextWithTemplate is for fine-grained control over usage messages. You generally don't need to use this.

func (*Application) UsageTemplate 

func (a *Application) UsageTemplate(template string) *Application

UsageTemplate specifies the text template to use when displaying usage information via --help. The default is DefaultUsageTemplate.

func (*Application) Version 

func (a *Application) Version(version string) *Application

Version adds a --version flag for displaying the application version.

func (*Application) Writers 

func (a *Application) Writers(out, err io.Writer) *Application

Writer specifies the writer to use for usage and errors. Defaults to os.Stderr.

type ApplicationModel 

type ApplicationModel struct {
	Name    string
	Help    string
	Version string
	Author  string
	*ArgGroupModel
	*CmdGroupModel
	*FlagGroupModel
}

func (*ApplicationModel) AppSummary 

func (a *ApplicationModel) AppSummary() string

func (*ApplicationModel) FindModelForCommand 

func (a *ApplicationModel) FindModelForCommand(cmd *CmdClause) *CmdModel

type ArgGroupModel 

type ArgGroupModel struct {
	Args []*ClauseModel
}

func (*ArgGroupModel) ArgSummary 

func (a *ArgGroupModel) ArgSummary() string

type Clause 

type Clause struct {
	// contains filtered or unexported fields
}

A Clause represents a flag or an argument passed by the user.

func Arg 

func Arg(name, help string) *Clause

Arg adds a new argument to the top-level of the default parser.

func Flag 

func Flag(name, help string) *Clause

Flag adds a new flag to the default parser.

func NewClause 

func NewClause(name, help string) *Clause

func (*Clause) Action 

func (c *Clause) Action(action Action) *Clause

func (*Clause) Bool 

func (p *Clause) Bool() (target *bool)

Bool parses the next command-line value as bool.

func (*Clause) BoolList 

func (p *Clause) BoolList() (target *[]bool)

BoolList accumulates bool values into a slice.

func (*Clause) BoolListVar 

func (p *Clause) BoolListVar(target *[]bool)

func (*Clause) BoolVar 

func (p *Clause) BoolVar(target *bool)

func (*Clause) Bytes 

func (c *Clause) Bytes() (target *units.Base2Bytes)

Bytes parses numeric byte units. eg. 1.5KB

func (*Clause) BytesVar 

func (c *Clause) BytesVar(target *units.Base2Bytes)

BytesVar parses numeric byte units. eg. 1.5KB

func (*Clause) Counter 

func (c *Clause) Counter() (target *int)

A Counter increments a number each time it is encountered.

func (*Clause) CounterVar 

func (c *Clause) CounterVar(target *int)

func (*Clause) Default 

func (c *Clause) Default(values ...string) *Clause

Default values for this flag. They *must* be parseable by the value of the flag.

func (*Clause) Duration 

func (p *Clause) Duration() (target *time.Duration)

Time duration.

func (*Clause) DurationList 

func (p *Clause) DurationList() (target *[]time.Duration)

DurationList accumulates time.Duration values into a slice.

func (*Clause) DurationListVar 

func (p *Clause) DurationListVar(target *[]time.Duration)

func (*Clause) DurationVar 

func (p *Clause) DurationVar(target *time.Duration)

func (*Clause) Enum 

func (c *Clause) Enum(options ...string) (target *string)

Enum allows a value from a set of options.

func (*Clause) EnumVar 

func (c *Clause) EnumVar(target *string, options ...string)

EnumVar allows a value from a set of options.

func (*Clause) Enums 

func (c *Clause) Enums(options ...string) (target *[]string)

Enums allows a set of values from a set of options.

func (*Clause) EnumsVar 

func (c *Clause) EnumsVar(target *[]string, options ...string)

EnumVar allows a value from a set of options.

func (*Clause) Envar 

func (c *Clause) Envar(name string) *Clause

Envar overrides the default value(s) for a flag from an environment variable, if it is set. Several default values can be provided by using new lines to separate them.

func (*Clause) ExistingDir 

func (c *Clause) ExistingDir() (target *string)

ExistingDir sets the parser to one that requires and returns an existing directory.

func (*Clause) ExistingDirVar 

func (c *Clause) ExistingDirVar(target *string)

ExistingDir sets the parser to one that requires and returns an existing directory.

func (*Clause) ExistingDirs 

func (p *Clause) ExistingDirs() (target *[]string)

ExistingDirs accumulates string values into a slice.

func (*Clause) ExistingDirsVar 

func (p *Clause) ExistingDirsVar(target *[]string)

func (*Clause) ExistingFile 

func (c *Clause) ExistingFile() (target *string)

ExistingFile sets the parser to one that requires and returns an existing file.

func (*Clause) ExistingFileOrDir 

func (c *Clause) ExistingFileOrDir() (target *string)

ExistingFileOrDir sets the parser to one that requires and returns an existing file OR directory.

func (*Clause) ExistingFileOrDirVar 

func (c *Clause) ExistingFileOrDirVar(target *string)

ExistingDir sets the parser to one that requires and returns an existing directory.

func (*Clause) ExistingFileVar 

func (c *Clause) ExistingFileVar(target *string)

ExistingFile sets the parser to one that requires and returns an existing file.

func (*Clause) ExistingFiles 

func (p *Clause) ExistingFiles() (target *[]string)

ExistingFiles accumulates string values into a slice.

func (*Clause) ExistingFilesOrDirs 

func (p *Clause) ExistingFilesOrDirs() (target *[]string)

ExistingFilesOrDirs accumulates string values into a slice.

func (*Clause) ExistingFilesOrDirsVar 

func (p *Clause) ExistingFilesOrDirsVar(target *[]string)

func (*Clause) ExistingFilesVar 

func (p *Clause) ExistingFilesVar(target *[]string)

func (*Clause) Float 

func (c *Clause) Float() (target *float64)

Float sets the parser to a float64 parser.

func (*Clause) Float32 

func (p *Clause) Float32() (target *float32)

Float32 parses the next command-line value as float32.

func (*Clause) Float32List 

func (p *Clause) Float32List() (target *[]float32)

Float32List accumulates float32 values into a slice.

func (*Clause) Float32ListVar 

func (p *Clause) Float32ListVar(target *[]float32)

func (*Clause) Float32Var 

func (p *Clause) Float32Var(target *float32)

func (*Clause) Float64 

func (p *Clause) Float64() (target *float64)

Float64 parses the next command-line value as float64.

func (*Clause) Float64List 

func (p *Clause) Float64List() (target *[]float64)

Float64List accumulates float64 values into a slice.

func (*Clause) Float64ListVar 

func (p *Clause) Float64ListVar(target *[]float64)

func (*Clause) Float64Var 

func (p *Clause) Float64Var(target *float64)

func (*Clause) FloatVar 

func (c *Clause) FloatVar(target *float64)

Float sets the parser to a float64 parser.

func (*Clause) GetEnvarValue 

func (c *Clause) GetEnvarValue() string

func (*Clause) GetSplitEnvarValue 

func (c *Clause) GetSplitEnvarValue() []string

func (*Clause) HasEnvarValue 

func (c *Clause) HasEnvarValue() bool

func (*Clause) HexBytes 

func (p *Clause) HexBytes() (target *[]byte)

Bytes as a hex string.

func (*Clause) HexBytesList 

func (p *Clause) HexBytesList() (target *[][]byte)

HexBytesList accumulates []byte values into a slice.

func (*Clause) HexBytesListVar 

func (p *Clause) HexBytesListVar(target *[][]byte)

func (*Clause) HexBytesVar 

func (p *Clause) HexBytesVar(target *[]byte)

func (*Clause) Hidden 

func (c *Clause) Hidden() *Clause

Hidden hides a flag from usage but still allows it to be used.

func (*Clause) HintAction 

func (c *Clause) HintAction(action HintAction) *Clause

HintAction registers a HintAction (function) for the flag to provide completions

func (*Clause) HintOptions 

func (c *Clause) HintOptions(options ...string) *Clause

HintOptions registers any number of options for the flag to provide completions

func (*Clause) Int 

func (p *Clause) Int() (target *int)

Int parses the next command-line value as int.

func (*Clause) Int16 

func (p *Clause) Int16() (target *int16)

Int16 parses the next command-line value as int16.

func (*Clause) Int16List 

func (p *Clause) Int16List() (target *[]int16)

Int16List accumulates int16 values into a slice.

func (*Clause) Int16ListVar 

func (p *Clause) Int16ListVar(target *[]int16)

func (*Clause) Int16Var 

func (p *Clause) Int16Var(target *int16)

func (*Clause) Int32 

func (p *Clause) Int32() (target *int32)

Int32 parses the next command-line value as int32.

func (*Clause) Int32List 

func (p *Clause) Int32List() (target *[]int32)

Int32List accumulates int32 values into a slice.

func (*Clause) Int32ListVar 

func (p *Clause) Int32ListVar(target *[]int32)

func (*Clause) Int32Var 

func (p *Clause) Int32Var(target *int32)

func (*Clause) Int64 

func (p *Clause) Int64() (target *int64)

Int64 parses the next command-line value as int64.

func (*Clause) Int64List 

func (p *Clause) Int64List() (target *[]int64)

Int64List accumulates int64 values into a slice.

func (*Clause) Int64ListVar 

func (p *Clause) Int64ListVar(target *[]int64)

func (*Clause) Int64Var 

func (p *Clause) Int64Var(target *int64)

func (*Clause) Int8 

func (p *Clause) Int8() (target *int8)

Int8 parses the next command-line value as int8.

func (*Clause) Int8List 

func (p *Clause) Int8List() (target *[]int8)

Int8List accumulates int8 values into a slice.

func (*Clause) Int8ListVar 

func (p *Clause) Int8ListVar(target *[]int8)

func (*Clause) Int8Var 

func (p *Clause) Int8Var(target *int8)

func (*Clause) IntVar 

func (p *Clause) IntVar(target *int)

func (*Clause) Ints 

func (p *Clause) Ints() (target *[]int)

Ints accumulates int values into a slice.

func (*Clause) IntsVar 

func (p *Clause) IntsVar(target *[]int)

func (*Clause) Model 

func (f *Clause) Model() *ClauseModel

func (*Clause) NoEnvar 

func (c *Clause) NoEnvar() *Clause

NoEnvar forces environment variable defaults to be disabled for this flag. Most useful in conjunction with app.DefaultEnvars().

func (*Clause) PlaceHolder 

func (c *Clause) PlaceHolder(placeholder string) *Clause

PlaceHolder sets the place-holder string used for flag values in the help. The default behaviour is to use the value provided by Default() if provided, then fall back on the capitalized flag name.

func (*Clause) PreAction 

func (c *Clause) PreAction(action Action) *Clause

PreAction callback executed

func (*Clause) Regexp 

func (p *Clause) Regexp() (target **regexp.Regexp)

Regexp parses the next command-line value as *regexp.Regexp.

func (*Clause) RegexpList 

func (p *Clause) RegexpList() (target *[]*regexp.Regexp)

RegexpList accumulates *regexp.Regexp values into a slice.

func (*Clause) RegexpListVar 

func (p *Clause) RegexpListVar(target *[]*regexp.Regexp)

func (*Clause) RegexpVar 

func (p *Clause) RegexpVar(target **regexp.Regexp)

func (*Clause) Required 

func (c *Clause) Required() *Clause

Required makes the flag required. You can not provide a Default() value to a Required() flag.

func (*Clause) SetValue 

func (c *Clause) SetValue(value Value)

func (*Clause) Short 

func (c *Clause) Short(name rune) *Clause

Short sets the short flag name.

func (*Clause) String 

func (p *Clause) String() (target *string)

String parses the next command-line value as string.

func (*Clause) StringMap 

func (c *Clause) StringMap() (target *map[string]string)

StringMap provides key=value parsing into a map.

func (*Clause) StringMapVar 

func (c *Clause) StringMapVar(target *map[string]string)

StringMap provides key=value parsing into a map.

func (*Clause) StringVar 

func (p *Clause) StringVar(target *string)

func (*Clause) Strings 

func (p *Clause) Strings() (target *[]string)

Strings accumulates string values into a slice.

func (*Clause) StringsVar 

func (p *Clause) StringsVar(target *[]string)

func (*Clause) URL 

func (c *Clause) URL() (target **url.URL)

URL provides a valid, parsed url.URL.

func (*Clause) URLList 

func (c *Clause) URLList() (target *[]*url.URL)

URLList provides a parsed list of url.URL values.

func (*Clause) URLListVar 

func (c *Clause) URLListVar(target *[]*url.URL)

URLListVar provides a parsed list of url.URL values.

func (*Clause) URLVar 

func (c *Clause) URLVar(target **url.URL)

URL provides a valid, parsed url.URL.

func (*Clause) Uint 

func (p *Clause) Uint() (target *uint)

Uint parses the next command-line value as uint.

func (*Clause) Uint16 

func (p *Clause) Uint16() (target *uint16)

Uint16 parses the next command-line value as uint16.

func (*Clause) Uint16List 

func (p *Clause) Uint16List() (target *[]uint16)

Uint16List accumulates uint16 values into a slice.

func (*Clause) Uint16ListVar 

func (p *Clause) Uint16ListVar(target *[]uint16)

func (*Clause) Uint16Var 

func (p *Clause) Uint16Var(target *uint16)

func (*Clause) Uint32 

func (p *Clause) Uint32() (target *uint32)

Uint32 parses the next command-line value as uint32.

func (*Clause) Uint32List 

func (p *Clause) Uint32List() (target *[]uint32)

Uint32List accumulates uint32 values into a slice.

func (*Clause) Uint32ListVar 

func (p *Clause) Uint32ListVar(target *[]uint32)

func (*Clause) Uint32Var 

func (p *Clause) Uint32Var(target *uint32)

func (*Clause) Uint64 

func (p *Clause) Uint64() (target *uint64)

Uint64 parses the next command-line value as uint64.

func (*Clause) Uint64List 

func (p *Clause) Uint64List() (target *[]uint64)

Uint64List accumulates uint64 values into a slice.

func (*Clause) Uint64ListVar 

func (p *Clause) Uint64ListVar(target *[]uint64)

func (*Clause) Uint64Var 

func (p *Clause) Uint64Var(target *uint64)

func (*Clause) Uint8 

func (p *Clause) Uint8() (target *uint8)

Uint8 parses the next command-line value as uint8.

func (*Clause) Uint8List 

func (p *Clause) Uint8List() (target *[]uint8)

Uint8List accumulates uint8 values into a slice.

func (*Clause) Uint8ListVar 

func (p *Clause) Uint8ListVar(target *[]uint8)

func (*Clause) Uint8Var 

func (p *Clause) Uint8Var(target *uint8)

func (*Clause) UintVar 

func (p *Clause) UintVar(target *uint)

func (*Clause) Uints 

func (p *Clause) Uints() (target *[]uint)

Uints accumulates uint values into a slice.

func (*Clause) UintsVar 

func (p *Clause) UintsVar(target *[]uint)

func (*Clause) UsageAction 

func (c *Clause) UsageAction(context *UsageContext) *Clause

UsageAction adds a PreAction() that will display the given UsageContext.

func (*Clause) UsageActionTemplate 

func (c *Clause) UsageActionTemplate(template string) *Clause

type ClauseModel 

type ClauseModel struct {
	Name        string
	Help        string
	Short       rune
	Default     []string
	Envar       string
	PlaceHolder string
	Required    bool
	Hidden      bool
	Value       Value
	Cumulative  bool
}

func (*ClauseModel) FormatPlaceHolder 

func (c *ClauseModel) FormatPlaceHolder() string

func (*ClauseModel) IsBoolFlag 

func (c *ClauseModel) IsBoolFlag() bool

func (*ClauseModel) String 

func (c *ClauseModel) String() string

type CmdClause 

type CmdClause struct {
	// contains filtered or unexported fields
}

A CmdClause is a single top-level command. It encapsulates a set of flags and either subcommands or positional arguments.

func Command 

func Command(name, help string) *CmdClause

Command adds a new command to the default parser.

func (*CmdClause) Action 

func (c *CmdClause) Action(action Action) *CmdClause

func (*CmdClause) Alias 

func (c *CmdClause) Alias(name string) *CmdClause

Add an Alias for this command.

func (*CmdClause) CmdCompletion 

func (c *CmdClause) CmdCompletion(context *ParseContext) []string

CmdCompletion returns completion options for arguments, if that's where parsing left off, or commands if there aren't any unsatisfied args.

func (*CmdClause) Command 

func (c *CmdClause) Command(name, help string) *CmdClause

Command adds a new sub-command.

func (*CmdClause) Default 

func (c *CmdClause) Default() *CmdClause

Default makes this command the default if commands don't match.

func (*CmdClause) FlagCompletion 

func (c *CmdClause) FlagCompletion(flagName string, flagValue string) (choices []string, flagMatch bool, optionMatch bool)

func (*CmdClause) FullCommand 

func (c *CmdClause) FullCommand() string

FullCommand returns the fully qualified "path" to this command, including interspersed argument placeholders. Does not include trailing argument placeholders.

eg. "signup <username> <email>"

func (*CmdClause) Hidden 

func (c *CmdClause) Hidden() *CmdClause

func (*CmdClause) Model 

func (c *CmdClause) Model(parent *CmdModel) *CmdModel

func (*CmdClause) OptionalSubcommands 

func (c *CmdClause) OptionalSubcommands() *CmdClause

OptionalSubcommands makes subcommands optional

func (*CmdClause) PreAction 

func (c *CmdClause) PreAction(action Action) *CmdClause

func (*CmdClause) Struct 

func (c *CmdClause) Struct(v interface{}) error

Struct allows applications to define flags with struct tags.

Supported struct tags are: help, placeholder, default, short, long, required, hidden, env, enum, and arg.

The name of the flag will default to the CamelCase name transformed to camel-case. This can be overridden with the "long" tag.

All basic Go types are supported including floats, ints, strings, time.Duration, and slices of same.

For compatibility, also supports the tags used by https://github.com/jessevdk/go-flags

func (*CmdClause) Validate 

func (c *CmdClause) Validate(validator CmdClauseValidator) *CmdClause

Validate sets a validation function to run when parsing.

type CmdClauseValidator 

type CmdClauseValidator func(*CmdClause) error

type CmdGroupModel 

type CmdGroupModel struct {
	Commands []*CmdModel
}

func (*CmdGroupModel) FlattenedCommands 

func (c *CmdGroupModel) FlattenedCommands() (out []*CmdModel)

type CmdModel 

type CmdModel struct {
	Name                string
	Aliases             []string
	Help                string
	Depth               int
	Hidden              bool
	Default             bool
	OptionalSubcommands bool
	Parent              *CmdModel
	*FlagGroupModel
	*ArgGroupModel
	*CmdGroupModel
}

func (*CmdModel) CmdSummary 

func (c *CmdModel) CmdSummary() string

func (*CmdModel) FullCommand 

func (c *CmdModel) FullCommand() string

FullCommand is the command path to this node, excluding positional arguments and flags.

func (*CmdModel) String 

func (c *CmdModel) String() string

type FlagGroupModel 

type FlagGroupModel struct {
	Flags []*ClauseModel
}

func (*FlagGroupModel) FlagSummary 

func (f *FlagGroupModel) FlagSummary() string

type Getter 

type Getter interface {
	Value
	Get() interface{}
}

Getter is an interface that allows the contents of a Value to be retrieved. It wraps the Value interface, rather than being part of it, because it appeared after Go 1 and its compatibility rules. All Value types provided by this package satisfy the Getter interface.

type HintAction 

type HintAction func() []string

HintAction is a function type who is expected to return a slice of possible command line arguments.

type OneOfClause 

type OneOfClause struct {
	Flag *Clause
	Arg  *Clause
	Cmd  *CmdClause
}

type ParseContext 

type ParseContext struct {
	SelectedCommand *CmdClause

	// Flags, arguments and commands encountered and collected during parse.
	Elements ParseElements
	// contains filtered or unexported fields
}

ParseContext holds the current context of the parser. When passed to Action() callbacks Elements will be fully populated with *FlagClause, *ArgClause and *CmdClause values and their corresponding arguments (if any).

func (*ParseContext) EOL 

func (p *ParseContext) EOL() bool

func (*ParseContext) HasTrailingArgs 

func (p *ParseContext) HasTrailingArgs() bool

HasTrailingArgs returns true if there are unparsed command-line arguments. This can occur if the parser can not match remaining arguments.

func (*ParseContext) LastCmd 

func (p *ParseContext) LastCmd(element *ParseElement) bool

LastCmd returns true if the element is the last (sub)command being evaluated.

func (*ParseContext) Next 

func (p *ParseContext) Next() *Token

Next token in the parse context.

func (*ParseContext) Peek 

func (p *ParseContext) Peek() *Token

func (*ParseContext) Push 

func (p *ParseContext) Push(token *Token) *Token

func (*ParseContext) String 

func (p *ParseContext) String() string

type ParseElement 

type ParseElement struct {
	// Clause associated with this element. Exactly one of these will be present.
	OneOf OneOfClause
	// Value is corresponding value for an argument or flag. For commands this value will be nil.
	Value *string
}

A ParseElement represents the parsers view of each element in the command-line argument slice.

type ParseElements 

type ParseElements []*ParseElement

ParseElements represents each element in the command-line argument slice.

func (ParseElements) ArgMap 

func (p ParseElements) ArgMap() map[string]*ParseElement

ArgMap collects all parsed positional arguments into a map keyed by long name.

func (ParseElements) FlagMap 

func (p ParseElements) FlagMap() map[string]*ParseElement

FlagMap collects all parsed flags into a map keyed by long name.

type Settings 

type Settings interface {
	SetValue(value Value)
}

type Token 

type Token struct {
	Index int
	Type  TokenType
	Value string
}

func (*Token) Equal 

func (t *Token) Equal(o *Token) bool

func (*Token) IsEOF 

func (t *Token) IsEOF() bool

func (*Token) IsFlag 

func (t *Token) IsFlag() bool

func (*Token) String 

func (t *Token) String() string

type TokenType 

type TokenType int
const (
	TokenShort TokenType = iota
	TokenLong
	TokenArg
	TokenError
	TokenEOL
)

Token types.

func (TokenType) String 

func (t TokenType) String() string

type UsageContext 

type UsageContext struct {
	// The text/template body to use.
	Template string
	// Indentation multiplier (defaults to 2 of omitted).
	Indent int
	// Width of wrap. Defaults wraps to the terminal.
	Width int
	// Funcs available in the template.
	Funcs template.FuncMap
	// Vars available in the template.
	Vars map[string]interface{}
}

UsageContext contains all of the context used to render a usage message.

type V 

type V map[string]interface{}

V is a convenience alias for translation function variables. eg. T("Something {{.Arg0}}", V{"Arg0": "moo"})

type Value 

type Value interface {
	String() string
	Set(string) error
}

Value is the interface to the dynamic value stored in a flag. (The default value is represented as a string.)

If a Value has an IsBoolFlag() bool method returning true, the command-line parser makes --name equivalent to -name=true rather than using the next command-line argument, and adds a --no-name counterpart for negating the flag.

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