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https://github.com/posener/cmd

The standard library flag package with its missing features
https://github.com/posener/cmd

cmd command flag go golang sub-command subcommands

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The standard library flag package with its missing features

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# cmd



[![codecov](https://codecov.io/gh/posener/cmd/branch/master/graph/badge.svg)](https://codecov.io/gh/posener/cmd)

[![GoDoc](https://img.shields.io/badge/pkg.go.dev-doc-blue)](http://pkg.go.dev/github.com/posener/cmd)



Package cmd is a minimalistic library that enables easy sub commands with the standard `flag` library.



This library extends the standard library `flag` package to support sub commands and more

features in a minimalistic and idiomatic API.



Features:



- [x] Sub commands.



- [x] Automatic bash completion.



- [x] Flag values definition and check.



- [x] Explicit positional arguments definition.



- [x] Automatic usage text.



## Usage



Define a root command object using the `New` function.

This object exposes the standard library's `flag.FlagSet` API, which enables adding flags in the

standard way.

Additionally, this object exposes the `SubCommand` method, which returns another command object.

This objects also exposing the same API, enabling definition of flags and nested sub commands.

The root object then have to be called with the `Parse` method, similarly to

the `flag.Parse` call.



## Principles



* Minimalistic and `flag`-like.



* Any flag that is defined in the base command will be reflected in all of its sub commands.



* When user types the command, it starts from the command and sub commands, only then types the

flags and then the positional arguments:



```go

[command] [sub commands...] [flags...] [positional args...]

```



* When a command defines positional arguments, all its sub commands has these positional

arguments and thus can't define their own positional arguments.



* When flag configuration is wrong, the program will panic.



## Examples



Definition and usage of sub commands and sub commands flags.



```golang

package main



import (

	"fmt"



	"github.com/posener/cmd"

)



var (

	// Define root command with a single string flag. This object the familiar standard library

	// `*flag.FlagSet` API, so it can be used similarly.

	root  = cmd.New()

	flag0 = root.String("flag0", "", "root string flag")



	// Define a sub command from the root command with a single string flag. The sub command object

	// also have the same API as the root command object.

	sub1  = root.SubCommand("sub1", "first sub command")

	flag1 = sub1.String("flag1", "", "sub1 string flag")



	// Define a second sub command from the root command with an int flag.

	sub2  = root.SubCommand("sub2", "second sub command")

	flag2 = sub1.Int("flag2", 0, "sub2 int flag")

)



// Definition and usage of sub commands and sub commands flags.

func main() {

	// Parse command line arguments.

	root.ParseArgs("cmd", "sub1", "-flag1", "value")



	// Check which sub command was choses by the user.

	switch {

	case sub1.Parsed():

		fmt.Printf("Called sub1 with flag: %s", *flag1)

	case sub2.Parsed():

		fmt.Printf("Called sub2 with flag: %d", *flag2)

	}

}



```



### Values



An example that shows how to use advanced configuration of flags and positional arguments using

the predict package.



```golang

package main



import (

	"fmt"

	"github.com/posener/cmd"

	"github.com/posener/complete/v2/predict"

)



func main() {

	// Should be defined in global `var`.

	var (

		root = cmd.New()

		// Define a flag with valid values 'foo' and 'bar', and enforce the values by `OptCheck()`.

		// The defined values will be used for bash completion, and since the OptCheck was set, the

		// flag value will be checked during the parse call.

		flag1 = root.String("flag1", "", "first flag", predict.OptValues("foo", "bar"), predict.OptCheck())

		// Define a flag to accept a valid Go file path. Choose to enforce the valid path using the

		// `OptCheck` function. The file name will also be completed in the bash completion

		// processes.

		file = root.String("file", "", "file path", predict.OptPredictor(predict.Files("*.go")), predict.OptCheck())

		// Positional arguments should be explicitly defined. Define positional arguments with valid

		// values of 'baz' and 'buzz', and choose not to enforce these values by not calling

		// `OptCheck`. These values will also be completed in the bash completion process.

		args = root.Args("[args...]", "positional arguments", predict.OptValues("baz", "buzz"))

	)



	// Parse fake command line arguments.

	root.ParseArgs("cmd", "-flag1", "foo", "-file", "cmd.go", "buz", "bazz")



	// Test:



	fmt.Println(*flag1, *file, *args)

}



```



 Output:



```

foo cmd.go [buz bazz]

```



### Args



In the cmd package, positional arguments should be explicitly defined. They are defined using the

`Args` or `ArgsVar` methods.



```golang

package main



import (

	"fmt"

	"github.com/posener/cmd"

)



func main() {

	// Should be defined in global `var`.

	var (

		root = cmd.New()

		// Positional arguments should be defined as any other flag.

		args = root.Args("[args...]", "positional arguments for command line")

	)



	// Parse fake command line arguments.

	root.ParseArgs("cmd", "v1", "v2", "v3")



	// Test:



	fmt.Println(*args)

}



```



 Output:



```

[v1 v2 v3]

```



### ArgsFn



An example of how to parse positional arguments using a custom function. It enables the advantage

of using named variables such as `src` and `dst` as opposed to args[0] and args[1].



```golang

package main



import (

	"fmt"

	"github.com/posener/cmd"

)



func main() {

	// Should be defined in global `var`.

	var (

		root = cmd.New()

		// Define variables that will hold the command line positional arguments.

		src, dst string

	)



	// Define an `ArgsFn` that converts a list of positional arguments to the named variables. It

	// should return an error when the arguments are invalid.

	argsFn := cmd.ArgsFn(func(args []string) error {

		if len(args) != 2 {

			return fmt.Errorf("expected src and dst, got %d arguments", len(args))

		}

		src, dst = args[0], args[1]

		return nil

	})



	// Should be in `init()`.

	// Register the function in the root command using the `ArgsVar` method.

	root.ArgsVar(argsFn, "[src] [dst]", "positional arguments for command line")



	// Should be in `main()`.

	root.ParseArgs("cmd", "from.txt", "to.txt")



	// Test:



	fmt.Println(src, dst)

}



```



 Output:



```

from.txt to.txt

```



### ArgsInt



An example of defining int positional arguments.



```golang

package main



import (

	"fmt"

	"github.com/posener/cmd"

)



func main() {

	// Should be defined in global `var`.

	var (

		root = cmd.New()

		// Define a variable that will hold the positional arguments values. Use the `ArgsInt` type

		// to parse them as int.

		args cmd.ArgsInt

	)



	// Should be in `init()`.

	// Register the positional argument variable in the root command using the `ArgsVar` method.

	root.ArgsVar(&args, "[int...]", "numbers to sum")



	// Should be in `main()`.

	// Parse fake command line arguments.

	root.ParseArgs("cmd", "10", "20", "30")



	// Test:



	sum := 0

	for _, n := range args {

		sum += n

	}

	fmt.Println(sum)

}



```



 Output:



```

60

```



### ArgsN



An example of defining an exact number of positional arguments.



```golang

package main



import (

	"fmt"

	"github.com/posener/cmd"

)



func main() {

	// Should be defined in global `var`.

	var (

		root = cmd.New()

		// Define a variable that will hold positional arguments. Create the `ArgsStr` object with

		// cap=2 to ensure that the number of arguments is exactly 2.

		args = make(cmd.ArgsStr, 2)

	)



	// Should be in `init()`.

	// Register the positional argument variable in the root command using the `ArgsVar` method

	// (similar to the Var methods of the standard library).

	root.ArgsVar(&args, "[src] [dst]", "positional arguments for command line")



	// Should be in `main()`.

	// Parse fake command line arguments.

	root.ParseArgs("cmd", "from.txt", "to.txt")



	// Test:



	fmt.Println(args)

}



```



 Output:



```

[from.txt to.txt]

```



---

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