Go 优秀库推荐 - 命令行工具

spf13/cobra 和 urfave/cli 是Go的2个优秀命令行工具：

两个项目的简介都挺有意思，各自的应用项目也很出色。我们一起来学一学，从docker和drone源码出发，了解如何使用。

spf13/cobra

spf13这个哥们，感觉是个印度人，但是很优秀的样子，下面是他的简介:

spf13 @golang at @google • Author, Speaker, Developer • Creator of Hugo, Cobra & spf13-vim • former Docker & MongoDB

吃鸡蛋不用了解母鸡，但是知道母鸡是那个厂的也很重要，开源项目也是如此。google、docker和mongodb，都是不错的技术公司，hugo也是不错博客平台，我的个人博客也是用它，感觉cobra有很棒的背景。闲聊结束，下面进入正题。

docker help 命令

一个好的命令行工具，首先要有一个很方便的 help指令，协助用户了解命令，这个最最重要。先看看 docker的帮助:

➜ ~ docker

Usage: docker [OPTIONS] COMMAND

A self-sufficient runtime for containers

Options:
--config string Location of client config files (default "/Users/tu/.docker")
-D, --debug Enable debug mode
-H, --host list Daemon socket(s) to connect to
-l, --log-level string Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info")
--tls Use TLS; implied by --tlsverify
--tlscacert string Trust certs signed only by this CA (default "/Users/tu/.docker/ca.pem")
--tlscert string Path to TLS certificate file (default "/Users/tu/.docker/cert.pem")
--tlskey string Path to TLS key file (default "/Users/tu/.docker/key.pem")
--tlsverify Use TLS and verify the remote
-v, --version Print version information and quit

Management Commands:
builder Manage builds
...
container Manage containers
...

Commands:
...
ps List containers
...

Run 'docker COMMAND --help' for more information on a command.

docker的帮助很详细的，这里为避免篇幅太长，省略了其中部分输出，保留重点分析介绍的命令(下同)，使用过程中非常方便。这种 help指令如何实现的呢。

从 docker-ce\components\cli\cmd\docker\docker.go的main函数开始:

func main() {
// Set terminal emulation based on platform as required.
stdin, stdout, stderr := term.StdStreams()
logrus.SetOutput(stderr)

dockerCli := command.NewDockerCli(stdin, stdout, stderr, contentTrustEnabled(), containerizedengine.NewClient)
cmd := newDockerCommand(dockerCli)

if err := cmd.Execute(); err != nil {
if sterr, ok := err.(cli.StatusError); ok {
if sterr.Status != "" {
fmt.Fprintln(stderr, sterr.Status)
}
// StatusError should only be used for errors, and all errors should
// have a non-zero exit status, so never exit with 0
if sterr.StatusCode == 0 {
os.Exit(1)
}
os.Exit(sterr.StatusCode)
}
fmt.Fprintln(stderr, err)
os.Exit(1)
}
}

代码非常清晰，做了三件事：1）读取命令行输入 2）解析查找命令 3）执行命令。

在 docker-ce\components\cli\cmd\docker\docker.go的newDockerCommand中，可以知道root命令的实现：

cmd := &cobra.Command{
Use: "docker [OPTIONS] COMMAND [ARG...]",
Short: "A self-sufficient runtime for containers",
SilenceUsage: true,
SilenceErrors: true,
TraverseChildren: true,
Args: noArgs,
RunE: func(cmd *cobra.Command, args []string) error {
return command.ShowHelp(dockerCli.Err())(cmd, args)
},
PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
// flags must be the top-level command flags, not cmd.Flags()
opts.Common.SetDefaultOptions(flags)
dockerPreRun(opts)
if err := dockerCli.Initialize(opts); err != nil {
return err
}
return isSupported(cmd, dockerCli)
},
Version: fmt.Sprintf("%s, build %s", cli.Version, cli.GitCommit),
DisableFlagsInUseLine: true,
}

从代码中可以清晰的把 Use和 Short命令输出对应起来。

顺便在 cobra.go查看到 docker help 命令

var helpCommand = &cobra.Command{
Use: "help [command]",
Short: "Help about the command",
PersistentPreRun: func(cmd *cobra.Command, args []string) {},
PersistentPostRun: func(cmd *cobra.Command, args []string) {},
RunE: func(c *cobra.Command, args []string) error {
cmd, args, e := c.Root().Find(args)
if cmd == nil || e != nil || len(args) > 0 {
return errors.Errorf("unknown help topic: %v", strings.Join(args, " "))
}

helpFunc := cmd.HelpFunc()
helpFunc(cmd, args)
return nil
},
}

以及 docker help 的模板输出

var usageTemplate = `Usage:

....

var helpTemplate = `
{{if or .Runnable .HasSubCommands}}{{.UsageString}}{{end}}`

这样，对 docker命令的输出，我们就大概了解了，对 cobra如何使用也有一个初略的了解。

docker 命令注册

继续查看docker各个子命令如何注册。docker.go的第62行，这里注册了所有的命令：

commands.AddCommands(cmd, dockerCli)

其对于实现在 command\commands\commands.go:

// AddCommands adds all the commands from cli/command to the root command
func AddCommands(cmd *cobra.Command, dockerCli command.Cli) {
cmd.AddCommand(
// checkpoint
checkpoint.NewCheckpointCommand(dockerCli),

// config
config.NewConfigCommand(dockerCli),

// container
container.NewContainerCommand(dockerCli),
container.NewRunCommand(dockerCli),

...

)
if runtime.GOOS == "linux" {
// engine
cmd.AddCommand(engine.NewEngineCommand(dockerCli))
}
}

一级命令都注册到 docker中了，继续查看一下 container这样的二级命令注册, 在 docker-ce\components\cli\command\container\cmd.go

// NewContainerCommand returns a cobra command for `container` subcommands
func NewContainerCommand(dockerCli command.Cli) *cobra.Command {
cmd := &cobra.Command{
Use: "container",
Short: "Manage containers",
Args: cli.NoArgs,
RunE: command.ShowHelp(dockerCli.Err()),
}
cmd.AddCommand(
NewAttachCommand(dockerCli),
NewCommitCommand(dockerCli),
NewCopyCommand(dockerCli),
NewCreateCommand(dockerCli),
NewDiffCommand(dockerCli),
NewExecCommand(dockerCli),
NewExportCommand(dockerCli),
NewKillCommand(dockerCli),
NewLogsCommand(dockerCli),
NewPauseCommand(dockerCli),
....
)
return cmd
}

可以清晰的看到 docker contianer 的子命令是一样是通过 AddCommand接口注册的。

docker ps 命令

docker ps, 这是个使用频率非常高的命令，帮助如下:

➜ ~ docker ps --help

Usage: docker ps [OPTIONS]

List containers

Options:
-a, --all Show all containers (default shows just running)
-f, --filter filter Filter output based on conditions provided
--format string Pretty-print containers using a Go template
-n, --last int Show n last created containers (includes all states) (default -1)
-l, --latest Show the latest created container (includes all states)
--no-trunc Don't truncate output
-q, --quiet Only display numeric IDs
-s, --size Display total file sizes

docker ps 实际上是 docker contianer ls 命令的别名，请看:

➜ ~ docker container --help

Usage: docker container COMMAND

Manage containers

Commands:
...
ls List containers
...

Run 'docker container COMMAND --help' for more information on a command.

可见 docker ps 和 docker container ls 的作用都是 Listcontainers。知道这个以后，查看代码：docker-ce\components\cli\command\container\ls.go 中有其实现:

// NewPsCommand creates a new cobra.Command for `docker ps`
func NewPsCommand(dockerCli command.Cli) *cobra.Command {
options := psOptions{filter: opts.NewFilterOpt()}

cmd := &cobra.Command{
Use: "ps [OPTIONS]",
Short: "List containers",
Args: cli.NoArgs,
RunE: func(cmd *cobra.Command, args []string) error {
return runPs(dockerCli, &options)
},
}

flags := cmd.Flags()

flags.BoolVarP(&options.quiet, "quiet", "q", false, "Only display numeric IDs")
flags.BoolVarP(&options.size, "size", "s", false, "Display total file sizes")
flags.BoolVarP(&options.all, "all", "a", false, "Show all containers (default shows just running)")
flags.BoolVar(&options.noTrunc, "no-trunc", false, "Don't truncate output")
flags.BoolVarP(&options.nLatest, "latest", "l", false, "Show the latest created container (includes all states)")
flags.IntVarP(&options.last, "last", "n", -1, "Show n last created containers (includes all states)")
flags.StringVarP(&options.format, "format", "", "", "Pretty-print containers using a Go template")
flags.VarP(&options.filter, "filter", "f", "Filter output based on conditions provided")

return cmd
}

结合 docker ps--help 的输出，可以猜测 Options和 Flags的对应关系。继续查看 BoolVarP的定义，在 spf13/pflag/bool.go

// BoolVarP is like BoolVar, but accepts a shorthand letter that can be used after a single dash.
func (f *FlagSet) BoolVarP(p *bool, name, shorthand string, value bool, usage string) {
flag := f.VarPF(newBoolValue(value, p), name, shorthand, usage)
flag.NoOptDefVal = "true"
}

配合注释说明，这样就非常清楚了，option名称使用 --速记名称使用 -。docker ps-a 和 docker ps--all 是一样的。

spf13/pflag 也是spf13 的一个库，主要处理参数量之类的。因为go是强类型的，所以用户的输入，都要合法的处理成go对应的数据类型。

在 ls.go 中还新建了一个命令，命名了 ps 是 container ls 的别名。

func newListCommand(dockerCli command.Cli) *cobra.Command {
cmd := *NewPsCommand(dockerCli)
cmd.Aliases = []string{"ps", "list"}
cmd.Use = "ls [OPTIONS]"
return &cmd
}

cobra的简单介绍就到这里，本次实验的 docker版本如下:

➜ ~ docker --version
Docker version 18.09.2, build 6247962

简单小结一下cobra使用:

• 采用命令模式
• 完善的帮助command及帮助option
• 支持选项及速记选项
• 命令支持别名

urfave/cli

drone help 命令

先看看 drone的帮助信息:

➜ ~ drone --help
NAME:
drone - command line utility

USAGE:
drone [global options] command [command options] [arguments...]

VERSION:
1.0.7

COMMANDS:
...
repo manage repositories
...

GLOBAL OPTIONS:
-t value, --token value server auth token [$DRONE_TOKEN]
-s value, --server value server address [$DRONE_SERVER]
--autoscaler value autoscaler address [$DRONE_AUTOSCALER]
--help, -h show help
--version, -v print the version

然后是 drone repo子命令:

➜ ~ drone repo
NAME:
drone repo - manage repositories

USAGE:
drone repo command [command options] [arguments...]

COMMANDS:
ls list all repos
info show repository details
enable enable a repository
update update a repository
disable disable a repository
repair repair repository webhooks
chown assume ownership of a repository
sync synchronize the repository list

OPTIONS:
--help, -h show help

再看看 drone repo ls二级子命令:

➜ rone repo ls --help
NAME:
drone repo ls - list all repos

USAGE:
drone repo ls [command options]

OPTIONS:
--format value format output (default: "{{ .Slug }}")
--org value filter by organization

drone 命令实现

drone-cli\drone\main.go中配置了一级子命令:

app.Commands = []cli.Command{
build.Command,
cron.Command,
log.Command,
encrypt.Command,
exec.Command,
info.Command,
repo.Command,
...
}

命令的解析执行:

if err := app.Run(os.Args); err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(1)
}

继续查看 repo\repo.go中：

// Command exports the repository command.
var Command = cli.Command{
Name: "repo",
Usage: "manage repositories",
Subcommands: []cli.Command{
repoListCmd,
repoInfoCmd,
repoAddCmd,
repoUpdateCmd,
repoRemoveCmd,
repoRepairCmd,
repoChownCmd,
repoSyncCmd,
},
}

可以看到 drone repo的子命令注册。

var repoListCmd = cli.Command{
Name: "ls",
Usage: "list all repos",
ArgsUsage: " ",
Action: repoList,
Flags: []cli.Flag{
cli.StringFlag{
Name: "format",
Usage: "format output",
Value: tmplRepoList,
},
cli.StringFlag{
Name: "org",
Usage: "filter by organization",
},
},
}

最后，再来了解一下命令如何查找，主要是下面2个函数。

根据名称查找命令：

// Command returns the named command on App. Returns nil if the command does not exist
func (a *App) Command(name string) *Command {
for _, c := range a.Commands {
if c.HasName(name) {
return &c
}
}

return nil
}

判断命令名称是否一致:

// HasName returns true if Command.Name or Command.ShortName matches given name
func (c Command) HasName(name string) bool {
for _, n := range c.Names() {
if n == name {
return true
}
}
return false
}

本次实验的drone版本是:

➜ ~ drone --version
drone version 1.0.7

简单小结一下cobra使用:

• 实现方式看起来更简单
• 也有完善的帮助command及帮助option

总结

spf13/cobra 和 urfave/cli 都挺棒的， urfave/cli 更简洁一些 ; spf13/cobra 支持 generator，协助生成项目，功能更强大一些。对Go感兴趣的同学，推荐都了解一下。

参考链接

What is the essential difference between urfave/cli и spf13/cobra?

Golang之使用Cobra

python命令行工具

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文章来源：https://mp.weixin.qq.com/s/r7G8cTWVjREqV5TzGwv_8Q