| Some command-line tools, like the `go` tool or `git` have many *subcommands*, each with its own set of flags. For example, `go build` and `go get` are two different subcommands of the `go` tool. The `flag` package lets us easily define simple subcommands that have their own flags. | ||
package main |
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import ( |
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"flag" |
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"fmt" |
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"os" |
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) |
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func main() { |
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| We declare a subcommand using the `NewFlagSet` function, and proceed to define new flags specific for this subcommand. | fooCmd := flag.NewFlagSet("foo", flag.ExitOnError) |
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fooEnable := fooCmd.Bool("enable", false, "enable") |
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fooName := fooCmd.String("name", "", "name") |
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| For a different subcommand we can define different supported flags. | barCmd := flag.NewFlagSet("bar", flag.ExitOnError) |
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barLevel := barCmd.Int("level", 0, "level") |
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| The subcommand is expected as the first argument to the program. | if len(os.Args) < 2 { |
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fmt.Println("expected 'foo' or 'bar' subcommands") |
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os.Exit(1) |
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} |
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| Check which subcommand is invoked. | switch os.Args[1] { |
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| For every subcommand, we parse its own flags and have access to trailing positional arguments. | case "foo": |
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fooCmd.Parse(os.Args[2:]) |
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fmt.Println("subcommand 'foo'") |
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fmt.Println(" enable:", *fooEnable) |
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fmt.Println(" name:", *fooName) |
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fmt.Println(" tail:", fooCmd.Args()) |
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case "bar": |
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barCmd.Parse(os.Args[2:]) |
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fmt.Println("subcommand 'bar'") |
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fmt.Println(" level:", *barLevel) |
expected 'foo' or 'bar' subcommands |
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fmt.Println(" tail:", barCmd.Args()) |
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default: |
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fmt.Println("expected 'foo' or 'bar' subcommands") |
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os.Exit(1) |
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} |
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} |