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https://github.com/jaffee/commandeer

Automatically sets up command line flags based on struct fields and tags.
https://github.com/jaffee/commandeer

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Automatically sets up command line flags based on struct fields and tags.

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## Commandeer

[![Go Report Card](https://goreportcard.com/badge/github.com/jaffee/commandeer)](https://goreportcard.com/report/github.com/jaffee/commandeer)

[![GoDoc](https://godoc.org/github.com/jaffee/commandeer?status.svg)](https://godoc.org/github.com/jaffee/commandeer)

[![Coverage](http://gocover.io/_badge/github.com/jaffee/commandeer)](https://gocover.io/github.com/jaffee/commandeer)



![Image](https://i.imgur.com/y6GmOGE.png)



Commandeer sets up command line flags based on struct fields and tags.



Do you...

 * like to develop Go apps as libraries with tiny main packages?

 * get frustrated keeping your flags up to date as your code evolves?

 * feel irked by the overlap between comments on struct fields and help strings for flags?

 * hate switching between your app's main and library packages?



You might like Commandeer. See the [godoc](https://godoc.org/github.com/jaffee/commandeer) for detailed usage, or just...



## Try It!

Here's how it works, define your app like so:

```go

package myapp



import "fmt"



type Main struct {

	Num     int    `help:"How many does it take?"`

	Vehicle string `help:"What did they get?"`

}



func NewMain() *Main { return &Main{Num: 5, Vehicle: "jeep"} }



func (m *Main) Run() error {

	if m.Num < 2 || m.Vehicle == "" {

		return fmt.Errorf("Need more gophers and/or vehicles.")

	}

	fmt.Printf("%d gophers stole my %s!\n", m.Num, m.Vehicle)

	return nil

}

```



and your main package:

```go

package main



import (

	"fmt"



	"github.com/jaffee/commandeer"

	"github.com/jaffee/commandeer/examples/myapp"

)



func main() {

	err := commandeer.Run(myapp.NewMain())

	if err != nil {

		fmt.Println(err)

	}

}

```



Now...

```bash

$ ./myapp -h

Usage of ./myapp:

  -num int

    	How many does it take? (default 5)

  -vehicle string

    	What did they get? (default "jeep")



$ ./myapp

5 gophers stole my jeep!

$ ./myapp -num 3 -vehicle horse

3 gophers stole my horse!

```



Notice that Commandeer set up the default values for each flag based on the

values in the struct passed to `Run`.



Commandeer is set up for minimal dependency pollution - it uses only stdlib

dependencies and is a few hundred lines of code itself. You need only import it

from a tiny `main` package (as in the example), and shouldn't need to reference

it anywhere else.



If you aren't allergic to external dependencies, you can also try

`github.com/jaffee/commandeer/cobrafy` which pulls in the excellent [Cobra](https://github.com/spf13/cobra) and

[pflag](https://github.com/spf13/pflag) packages giving you GNU/POSIX style flags and some other nice features

should you care to use them. See the [godoc](https://godoc.org/github.com/jaffee/commandeer/cobrafy), or the [myapp-cobrafy example](https://github.com/jaffee/commandeer/blob/master/examples/myapp/cmd/myapp-cobrafy/main.go).



## Features

In addition to the `help` struct tag, you can use `flag` to override the computed flag name, e.g.



```go

type Main struct {

	Num     int    `flag:"number"`

}

```



You can also use `flag:"-"` to explicitly ignore fields from being used as flags, e.g.

```go

type Main struct {

	Num     int    `flag:"-"`

}

```



Nested structs are supported, by default the field names will be joined with "." to create the flag name, e.g.



```go

type Main struct {

	Vehicle struct {

		Color string

		Weight int

	}

}

```



produces:



```

  -vehicle.color string

    	

  -vehicle.weight int

```



If you wish to avoid this prefix behavior (e.g. if you have an embedded struct field and you want to elevate its fields to the top level) you can use `flag:"!embed"`, e.g.



```go

type Main struct {

	Vehicle struct {

		Color string

		Weight int

	} `flag:"!embed"`

}

```



which will produce:

```

  -color string

    	

  -weight int

```



## Contributing

Yes please!



For small stuff, feel free to submit a PR directly. For larger things,

especially API changes, it's best to make an issue first so it can be discussed.



## Similar projects



 * https://github.com/anacrolix/tagflag

 * https://github.com/octago/sflags