- Overview
- Features
- User-visible changes between v1 and v2
- API changes between v1 and v2
- Versions
- Change History
- Examples
- Reference Documentation
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 --
).
- 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()
). - Support for required flags and required positional arguments (
kingpin.Flag("f", "").Required().Int()
). - 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 (
--man-page
).
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
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.
ParseWithFileExpansion()
is gone. The new parser directly supports expanding@<file>
.- Added
FatalUsage()
andFatalUsageContext()
for displaying an error + usage and terminating. Dispatch()
renamed toAction()
.- 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:DefaultUsageTemplate
- default template.CompactUsageTemplate
- compact command template for larger applications.
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
-
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")
.
- Pass any value through to
-
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
toPlaceHolder
. - Removed
MetaVarFromDefault
. Kingpin now uses heuristics to determine what to display.
- Renamed
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)
}
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)
}
}
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.
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":
}
}
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 = new(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'))
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 a
string, which is parsed by the value itself, so it must be compliant with
the format expected.
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()
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
Kingpin supports this by having Value
provide a IsCumulative() bool
function. If this function exists and returns true, the value parser will be
called repeatedly for every remaining argument.
Examples of this are the Strings()
and StringMap()
values.
To implement the above example 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."))
Kingpin v2 supports templatised help using the text/template library (actually, a fork).
You can specify the template to use with the Application.UsageTemplate() function.
There are three 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.
$ 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.
$ 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>