go-cli

go-cli is a package to build a CLI application. Support command/sub-commands.

Some applications are built using go-cli including:

• frep
• mknovel
• ovfenv-installer
• publish-toolset

Table of Contents

• Installation
• Syntax for Command Line
• Getting Started
  • Arguments
  • Flags
    • Bool flag
    • Value bind
    • Short, Long, Alias Names
    • Placeholder
    • Default Value
    • NoOptDefVal
    • Hidden flags
  • Commands
• Generate Help
  • Customize help
• Generate Version
  • Customize version
• Error Handler
  • OnCommandNotFound
  • OnActionPanic
• Contributing
• License

Installation

go-cli is available using the standard go get command.

To install go-cli, simply run:

go get github.com/subchen/go-cli/v3

Syntax for Command Line

// Long option
--flag    // boolean flags, or flags with no option default values
--flag x  // only on flags without a default value
--flag=x

// Short option
-x        // boolean flags
-x 123
-x=123
-x123     // value is 123

// value wrapped by quote
-x="123"
-x='123'

// unordered in flags and arguments
arg1 -x 123 arg2 --test arg3 arg4

// stops parsing after the terminator `--`
-x 123 -- arg1 --not-a-flag arg3 arg4

Getting Started

A simple CLI application:

package main

import (
    "fmt"
    "os"
    "github.com/subchen/go-cli/v3"
)

func main() {
    app := cli.NewApp()
    app.Name = "hello"
    app.Version = "1.0.0"
    app.Usage = "a hello world application."
    app.Action = func(c *cli.Context) {
        fmt.Println("Hello World!")
    }
    app.Run(os.Args)
}

Build and run our new CLI application

$ go build
$ ./hello
Hello World!

go-cli also generates neat help text

$ ./hello --help
NAME:
    hello - a hello world application.

USAGE:
    hello [options] [arguments...]

VERSION:
    1.0.0

OPTIONS:
    --help     print this help
    --version  print version information

Arguments

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

app := cli.NewApp()

app.Action = func(c *cli.Context) {
    name := c.Args()[0]
    fmt.Printf("Hello %v\n", name)
}

app.Run(os.Args)

Flags

Setting and querying flags is simple.

app := cli.NewApp()

app.Flags = []*cli.Flag {
    {
        Name: "name",
        Usage: "a name of user",
    },
}

app.Action = func(c *cli.Context) {
    name := c.GetString("name")
    fmt.Printf("Hello %v\n", name)
}

app.Run(os.Args)

Bool flag

A bool flag can has a optional inline bool value.

&cli.Flag{
    Name: "verbose",
    Usage: "output verbose information",
    IsBool: true,
},

The parsed arguments likes:

// valid
--verbose
--verbose=true
--verbose=false

// invalid
--verbose false

bool flag accepts 1,t,true,yes,on as true, 0,f,false,no,off as false.

Value bind

You can bind a variable for a Flag.Value, which will be set after parsed.

var name string

app := cli.NewApp()

app.Flags = []*cli.Flag {
    {
        Name: "name",
        Usage: "a name of user",
        Value: &name,
    },
}

app.Action = func(c *cli.Context) {
    fmt.Printf("Hello %v\n", name)
}

app.Run(os.Args)

Flag.Value can accept a cli.Value interface or a pointer of base type.

• base type:

  • *string
  • *bool
  • *int, *int8, *int16, *int32, *int64
  • *uint, *uint8, *uint16, *uint32, *uint64
  • *float32, *float64
  • *time.Time, *time.Duration, *time.Location
  • *net.IP, *net.IPMask, *net.IPNet
  • *url.URL

• slice of base type:

  • *[]string
  • *[]int, *[]uint, *[]float64
  • *[]net.IP, *[]net.IPNet
  • *[]url.URL

• cli.Value:

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

Note: If you set *bool as Flag.Value, the Flag.IsBool will be automatically true.

Short, Long, Alias Names

You can set multiply name in a flag, a short name, a long name, or multiple alias names.

&cli.Flag{
    Name: "o, output, output-dir",
    Usage: "A directory for output",
}

Then, results in help output like:

-o, --output, --output-dir value   A directory for output

Placeholder

Sometimes it's useful to specify a flag's value within the usage string itself.

For example this:

&cli.Flag{
    Name: "o, output",
    Usage: "A directory for output",
    Placeholder: "DIR",
}

Then, results in help output like:

-o DIR, --output DIR   A directory for output

Default Value

&cli.Flag{
    Name: "o, output",
    Usage: "A directory for output",
    DefValue: "/tmp/",
}

You also can set a default value got from the Environment

&cli.Flag{
    Name: "o, output",
    Usage: "A directory for output",
    EnvVar: "APP_OUTPUT_DIR",
}

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

EnvVar: "APP_OUTPUT,APP_OUTPUT_DIR",

NoOptDefVal

If a flag has a NoOptDefVal and the flag is set on the command line without an option the flag will be set to the NoOptDefVal.

For example given:

&cli.Flag{
    Name: "flagname",
    DefValue: "123",
    NoOptDefVal: "456",
    Value: &val
}

Would result in something like

Parsed Arguments	Resulting Value
--flagname=000	val=000
--flagname	val=456
[nothing]	val=123

Hidden flags

It is possible to mark a flag as hidden, meaning it will still function as normal, however will not show up in usage/help text.

&cli.Flag{
    Name: "secretFlag",
    Hidden: true,
}

Commands

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

package main

import (
    "fmt"
    "os"
    "strings"
    "github.com/subchen/go-cli/v3"
)

func main() {
    app := cli.NewApp()
    app.Name = "git"
    app.Commands = []*cli.Command{
        {
            Name:   "add",
            Usage:  "Add file contents to the index",
            Action: func(c *cli.Context) {
                fmt.Println("added files: ", strings.Join(c.Args(), ", "))
            },
        },
        {
            // alias name
            Name:   "commit, co",
            Usage:  "Record changes to the repository",
            Flags:  []*cli.Flag {
                {
                    Name: "m, message",
                    Usage: "commit message",
                },
            },
            Hidden: false,
            Action: func(c *cli.Context) {
                fmt.Println("commit message: ", c.GetString("m"))
            },
        },
    }

    app.SeeAlso = `https://github.com/subchen/go-cli
https://github.com/subchen/go-cli/wiki`

    app.Run(os.Args)
}

Also, you can use sub-commands in a command.

Generate Help

The default help flag (--help) is defined in cli.App and cli.Command.

Customize help

All of the help text generation may be customized. A help template is exposed as variable cli.HelpTemplate, that can be override.

// Append copyright
cli.HelpTemplate = cli.HelpTemplate + "@2017 Your company, Inc.\n\n"

Or, you can rewrite a help using customized func.

app := cli.NewApp()

app.ShowHelp = func(c *cli.HelpContext) {
    fmt.Println("this is my help generated.")
}

app.Run(os.Args)

Generate Version

The default version flag (--version) is defined in cli.App.

app := cli.NewApp()
app.Name = "hello"
app.Version = "1.0.0"
app.BuildInfo = &cli.BuildInfo{
    GitBranch:   "master",
    GitCommit:   "320279c1a9a6537cdfd1e526063f6a748bb1fec3",
    GitRevCount: "1234",
    Timestamp:   "Sat May 13 19:53:08 UTC 2017",
}
app.Run(os.Args)

Then, ./hello --version results like:

Name:       hello
Version:    1.0.0
Patches:    1234
Git branch: master
Git commit: 320279c1a9a6537cdfd1e526063f6a748bb1fec3
Built:      Sat May 13 19:53:08 UTC 2017
Go version: go1.8.1
OS/Arch:    darwin/amd64

Customize version

You can rewrite version output using customized func.

app := cli.NewApp()

app.ShowVersion = func(app *App) {
    fmt.Println("Version: ", app.Version)
}

app.Run(os.Args)

Error Handler

OnCommandNotFound

go-cli provides OnCommandNotFound func to handle an error if command/sub-command is not found.

app := cli.NewApp()
app.Flags = ...
app.Commands = ...

app.OnCommandNotFound = func(c *cli.Context, command string) {
    c.ShowError(fmt.Errorf("Command not found: %s", command))
}

app.Run(os.Args)

OnActionPanic

go-cli provides OnActionPanic func to handle an error if panic in action.

app := cli.NewApp()
app.Flags = ...
app.Commands = ...

app.OnActionPanic = func(c *cli.Context, err error) {
    os.Stderr.WriteString(fmt.Sprintf("fatal: %v\n", err))
}

app.Run(os.Args)

Notes: go-cli will only output error message without golang error stacks if app.OnActionPanic is nil.

Contributing

• Fork it
• Create your feature branch (git checkout -b my-new-feature)
• Commit your changes (git commit -am 'Add some feature')
• Push to the branch (git push origin my-new-feature)
• Create new Pull Request

License

Apache 2.0 license. See LICENSE