forked from mirror/cobra
398 lines
13 KiB
Markdown
398 lines
13 KiB
Markdown
# Cobra
|
||
|
||
A Commander for modern go CLI interactions
|
||
|
||
[](https://travis-ci.org/spf13/cobra)
|
||
|
||
## Overview
|
||
|
||
Cobra is a commander providing a simple interface to create powerful modern CLI
|
||
interfaces similar to git & go tools. In addition to providing an iterface, Cobra
|
||
simultaneously provides a controller to organize your application code.
|
||
|
||
Inspired by go, go-Commander, gh and subcommand, Cobra improves on these by
|
||
providing **fully posix compliant flags** (including short & long versions),
|
||
**nesting commands**, and the ability to **define your own help and usage** for any or
|
||
all commands.
|
||
|
||
Cobra has an exceptionally clean interface and simple design without needless
|
||
constructors or initialization methods.
|
||
|
||
Applications built with Cobra commands are designed to be as user friendly as
|
||
possible. Flags can be placed before or after the command (as long as a
|
||
confusing space isn’t provided). Both short and long flags can be used. A
|
||
command need not even be fully typed. The shortest unambiguous string will
|
||
suffice. Help is automatically generated and available for the application or
|
||
for a specific command using either the help command or the --help flag.
|
||
|
||
## Concepts
|
||
|
||
Cobra is built on a structure of commands & flags.
|
||
|
||
**Commands** represent actions and **Flags** are modifiers for those actions.
|
||
|
||
In the following example 'server' is a command and 'port' is a flag.
|
||
|
||
hugo server --port=1313
|
||
|
||
### Commands
|
||
|
||
Command is the central point of the application. Each interaction that
|
||
the application supports will be contained in a Command. A command can
|
||
have children commands and optionally run an action.
|
||
|
||
In the example above 'server' is the command
|
||
|
||
A Command has the following structure:
|
||
|
||
type Command struct {
|
||
Use string // The one-line usage message.
|
||
Short string // The short description shown in the 'help' output.
|
||
Long string // The long message shown in the 'help <this-command>' output.
|
||
Run func(cmd *Command, args []string) // Run runs the command.
|
||
}
|
||
|
||
### Flags
|
||
|
||
A Flag is a way to modify the behavior of an command. Cobra supports
|
||
fully posix compliant flags as well as the go flag package.
|
||
A Cobra command can define flags that persist through to children commands
|
||
and flags that are only available to that command.
|
||
|
||
In the example above 'port' is the flag.
|
||
|
||
Flag functionality is provided by the [pflag
|
||
libary](https://github.com/ogier/pflag), a fork of the flag standard library
|
||
which maintains the same interface while adding posix compliance.
|
||
|
||
## Usage
|
||
|
||
Cobra works by creating a set of commands and then organizing them into a tree.
|
||
The tree defines the structure of the application.
|
||
|
||
Once each command is defined with it's corresponding flags, then the
|
||
tree is assigned to the commander which is finally executed.
|
||
|
||
### Installing
|
||
Using Cobra is easy. First use go get to install the latest version
|
||
of the library.
|
||
|
||
$ go get github.com/spf13/cobra
|
||
|
||
Next include cobra in your application.
|
||
|
||
import "github.com/spf13/cobra"
|
||
|
||
### Create the root command
|
||
|
||
The root command represents your binary itself.
|
||
|
||
Cobra doesn't require any special constructors. Simply create your commands.
|
||
|
||
var HugoCmd = &cobra.Command{
|
||
Use: "hugo",
|
||
Short: "Hugo is a very fast static site generator",
|
||
Long: `A Fast and Flexible Static Site Generator built with
|
||
love by spf13 and friends in Go.
|
||
Complete documentation is available at http://hugo.spf13.com`,
|
||
Run: func(cmd *cobra.Command, args []string) {
|
||
// Do Stuff Here
|
||
},
|
||
}
|
||
|
||
### Create additional commands
|
||
|
||
Additional commands can be defined.
|
||
|
||
var versionCmd = &cobra.Command{
|
||
Use: "version",
|
||
Short: "Print the version number of Hugo",
|
||
Long: `All software has versions. This is Hugo's`,
|
||
Run: func(cmd *cobra.Command, args []string) {
|
||
fmt.Println("Hugo Static Site Generator v0.9 -- HEAD")
|
||
},
|
||
}
|
||
|
||
### Attach command to its parent
|
||
In this example we are attaching it to the root, but commands can be attached at any level.
|
||
|
||
HugoCmd.AddCommand(versionCmd)
|
||
|
||
### Assign flags to a command
|
||
|
||
Since the flags are defined and used in different locations, we need to define a variable outside with the correct scope to assign the flag to work with.
|
||
|
||
var Verbose bool
|
||
var Source string
|
||
|
||
There are two different approaches to assign a flag.
|
||
|
||
#### Persistent Flags
|
||
|
||
A flag can be 'persistent' meaning that this flag will be available to the
|
||
command it's assigned to as well as every command under that command. For
|
||
global flags assign a flag as a persistent flag on the root.
|
||
|
||
HugoCmd.PersistentFlags().BoolVarP(&Verbose, "verbose", "v", false, "verbose output")
|
||
|
||
#### Local Flags
|
||
|
||
A flag can also be assigned locally which will only apply to that specific command.
|
||
|
||
HugoCmd.Flags().StringVarP(&Source, "source", "s", "", "Source directory to read from")
|
||
|
||
### Once all commands and flags are defined, Execute the commands
|
||
|
||
Execute should be run on the root for clarity, though it can be called on any command.
|
||
|
||
HugoCmd.Execute()
|
||
|
||
## Example
|
||
|
||
In the example below we have defined three commands. Two are at the top level
|
||
and one (cmdTimes) is a child of one of the top commands. In this case the root
|
||
is not executible meaning that a subcommand is required. This is accomplished
|
||
by not providing a 'Run' for the 'rootCmd'.
|
||
|
||
We have only defined one flag for a single command.
|
||
|
||
More documentation about flags is available at https://github.com/spf13/pflag
|
||
|
||
import(
|
||
"github.com/spf13/cobra"
|
||
"fmt"
|
||
"strings"
|
||
)
|
||
|
||
func main() {
|
||
|
||
var echoTimes int
|
||
|
||
var cmdPrint = &cobra.Command{
|
||
Use: "print [string to print]",
|
||
Short: "Print anything to the screen",
|
||
Long: `print is for printing anything back to the screen.
|
||
For many years people have printed back to the screen.
|
||
`,
|
||
Run: func(cmd *cobra.Command, args []string) {
|
||
fmt.Println("Print: " + strings.Join(args, " "))
|
||
},
|
||
}
|
||
|
||
var cmdEcho = &cobra.Command{
|
||
Use: "echo [string to echo]",
|
||
Short: "Echo anything to the screen",
|
||
Long: `echo is for echoing anything back.
|
||
Echo works a lot like print, except it has a child command.
|
||
`,
|
||
Run: func(cmd *cobra.Command, args []string) {
|
||
fmt.Println("Print: " + strings.Join(args, " "))
|
||
},
|
||
}
|
||
|
||
var cmdTimes = &cobra.Command{
|
||
Use: "times [# times] [string to echo]",
|
||
Short: "Echo anything to the screen more times",
|
||
Long: `echo things multiple times back to the user by providing
|
||
a count and a string.`,
|
||
Run: func(cmd *cobra.Command, args []string) {
|
||
for i:=0; i < echoTimes; i++ {
|
||
fmt.Println("Echo: " + strings.Join(args, " "))
|
||
}
|
||
},
|
||
}
|
||
|
||
cmdTimes.Flags().IntVarP(&echoTimes, "times", "t", 1, "times to echo the input")
|
||
|
||
var rootCmd = &cobra.Command{Use: "app"}
|
||
rootCmd.AddCommand(cmdPrint, cmdEcho)
|
||
cmdEcho.AddCommand(cmdTimes)
|
||
rootCmd.Execute()
|
||
}
|
||
|
||
For a more complete example of a larger application, please checkout [Hugo](http://hugo.spf13.com)
|
||
|
||
## The Help Command
|
||
|
||
Cobra automatically adds a help command to your application.
|
||
This will be called when a user runs 'app help'. Additionally help will also
|
||
support all other commands as input. Say for instance you have a command called
|
||
'create' without any additional configuration cobra will work when 'app help
|
||
create' is called.
|
||
|
||
### Example
|
||
|
||
The following output is automatically generated by cobra. Nothing beyond the
|
||
command and flag definitions are needed.
|
||
|
||
> hugo help
|
||
|
||
A Fast and Flexible Static Site Generator built with
|
||
love by spf13 and friends in Go.
|
||
|
||
Complete documentation is available at http://hugo.spf13.com
|
||
|
||
Usage:
|
||
hugo [flags]
|
||
hugo [command]
|
||
|
||
Available Commands:
|
||
server :: Hugo runs it's own a webserver to render the files
|
||
version :: Print the version number of Hugo
|
||
check :: Check content in the source directory
|
||
benchmark :: Benchmark hugo by building a site a number of times
|
||
help [command] :: Help about any command
|
||
|
||
Available Flags:
|
||
-b, --base-url="": hostname (and path) to the root eg. http://spf13.com/
|
||
-D, --build-drafts=false: include content marked as draft
|
||
--config="": config file (default is path/config.yaml|json|toml)
|
||
-d, --destination="": filesystem path to write files to
|
||
-s, --source="": filesystem path to read files relative from
|
||
--stepAnalysis=false: display memory and timing of different steps of the program
|
||
--uglyurls=false: if true, use /filename.html instead of /filename/
|
||
-v, --verbose=false: verbose output
|
||
-w, --watch=false: watch filesystem for changes and recreate as needed
|
||
|
||
Use "hugo help [command]" for more information about that command.
|
||
|
||
|
||
|
||
Help is just a command like any other. There is no special logic or behavior
|
||
around it. In fact you can provide your own if you want.
|
||
|
||
### Defining your own help
|
||
|
||
You can provide your own Help command or you own template for the default command to use.
|
||
|
||
The default help command is
|
||
|
||
func (c *Command) initHelp() {
|
||
if c.helpCommand == nil {
|
||
c.helpCommand = &Command{
|
||
Use: "help [command]",
|
||
Short: "Help about any command",
|
||
Long: `Help provides help for any command in the application.
|
||
Simply type ` + c.Name() + ` help [path to command] for full details.`,
|
||
Run: c.HelpFunc(),
|
||
}
|
||
}
|
||
c.AddCommand(c.helpCommand)
|
||
}
|
||
|
||
You can provide your own command, function or template through the following methods.
|
||
|
||
command.SetHelpCommand(cmd *Command)
|
||
|
||
command.SetHelpFunc(f func(*Command, []string))
|
||
|
||
command.SetHelpTemplate(s string)
|
||
|
||
The latter two will also apply to any children commands.
|
||
|
||
## Usage
|
||
|
||
When the user provides an invalid flag or invalid command Cobra responds by
|
||
showing the user the 'usage'
|
||
|
||
### Example
|
||
You may recognize this from the help above. That's because the default help
|
||
embeds the usage as part of it's output.
|
||
|
||
Usage:
|
||
hugo [flags]
|
||
hugo [command]
|
||
|
||
Available Commands:
|
||
server Hugo runs it's own a webserver to render the files
|
||
version Print the version number of Hugo
|
||
check Check content in the source directory
|
||
benchmark Benchmark hugo by building a site a number of times
|
||
help [command] Help about any command
|
||
|
||
Available Flags:
|
||
-b, --base-url="": hostname (and path) to the root eg. http://spf13.com/
|
||
-D, --build-drafts=false: include content marked as draft
|
||
--config="": config file (default is path/config.yaml|json|toml)
|
||
-d, --destination="": filesystem path to write files to
|
||
-s, --source="": filesystem path to read files relative from
|
||
--stepAnalysis=false: display memory and timing of different steps of the program
|
||
--uglyurls=false: if true, use /filename.html instead of /filename/
|
||
-v, --verbose=false: verbose output
|
||
-w, --watch=false: watch filesystem for changes and recreate as needed
|
||
|
||
### Defining your own usage
|
||
You can provide your own usage function or template for cobra to use.
|
||
|
||
The default usage function is
|
||
|
||
return func(c *Command) error {
|
||
err := tmpl(c.Out(), c.UsageTemplate(), c)
|
||
return err
|
||
}
|
||
|
||
Like help the function and template are over ridable through public methods.
|
||
|
||
command.SetUsageFunc(f func(*Command) error)
|
||
|
||
command.SetUsageTemplate(s string)
|
||
|
||
|
||
## Debugging
|
||
|
||
Cobra provides a ‘DebugFlags’ method on a command which when called will print
|
||
out everything Cobra knows about the flags for each command
|
||
|
||
### Example
|
||
|
||
command.DebugFlags()
|
||
|
||
## Release Notes
|
||
* **0.9.0** June 17, 2014
|
||
* flags can appears anywhere in the args (provided they are unambiguous)
|
||
* --help prints usage screen for app or command
|
||
* Prefix matching for commands
|
||
* Cleaner looking help and usage output
|
||
* Extensive test suite
|
||
* **0.8.0** Nov 5, 2013
|
||
* Reworked interface to remove commander completely
|
||
* Command now primary structure
|
||
* No initialization needed
|
||
* Usage & Help templates & functions definable at any level
|
||
* Updated Readme
|
||
* **0.7.0** Sept 24, 2013
|
||
* Needs more eyes
|
||
* Test suite
|
||
* Support for automatic error messages
|
||
* Support for help command
|
||
* Support for printing to any io.Writer instead of os.Stderr
|
||
* Support for persistent flags which cascade down tree
|
||
* Ready for integration into Hugo
|
||
* **0.1.0** Sept 3, 2013
|
||
* Implement first draft
|
||
|
||
## ToDo
|
||
* Launch proper documentation site
|
||
|
||
## Contributing
|
||
|
||
1. Fork it
|
||
2. Create your feature branch (`git checkout -b my-new-feature`)
|
||
3. Commit your changes (`git commit -am 'Add some feature'`)
|
||
4. Push to the branch (`git push origin my-new-feature`)
|
||
5. Create new Pull Request
|
||
|
||
## Contributors
|
||
|
||
Names in no particular order:
|
||
|
||
* [spf13](https://github.com/spf13)
|
||
|
||
## License
|
||
|
||
Cobra is released under the Apache 2.0 license. See [LICENSE.txt](https://github.com/spf13/cobra/blob/master/LICENSE.txt)
|
||
|
||
|
||
[](https://bitdeli.com/free "Bitdeli Badge")
|
||
|