flaggy

Flaggy is a command line parser that has been inspired by go-flags (https://github.com/jessevdk/go-flags). Flaggy has been designed with the purpose of binding behavior to data when parsing command line arguments in order to make the user interaction logic cleaner and simpler to maintain. Furthermore, Flaggy also allows for creating nested commands and multiple levels of flags when required.

Option (Flag) Definition

Defining options (flags) in Flaggy is identical to go-flags. In order to define options, a struct has to be created whose fields represent the data required to be collected from the user and parsed from command line arguments. These fields are decorated with tags in order to define to which command they belong and what their purpose are. For exampe

type Options struct {
    Help bool `long:"help" short:"-h" help:"Shows help"`    
}

Parsing

Parsing options (flags) is as easy as calling the Parse method. For example:

type Options struct {
    Help bool `long:"help" short:"-h" help:"Shows help"`    
}
options := Options {}
err := flaggy.Parse(&options, os.Args[1:])

You can also verify if any argument has been parsed successfully using the Parsed method.

Supported Data Types

Flaggy has limited support for Go's data types. The following table lists out all data types that are currently supported by Flaggy:

• int
• *int
• int32
• *int32
• int64
• *int64
• int16
• *int16
• int8
• *int8
• uint
• *uint
• uint32
• *uint32
• uint64
• *uint64
• uint16
• *uint16
• uint8
• *uint8
• float32
• *float32
• float64
• *float64
• comples64
• *comples64
• complex128
• *complex128
• string
• *string
• bool
• *bool
• struct
• *struct
• slice/array
• *slice/*array

Slices or arrays of structs are not supported

Nested Options

Similar to any other command line interfaces (i.e. kubectl, docker, etc.), Flaggy allows for grouping commands. For instance, the following command read -f abc.txt --skip-white-space can be created as:

type Options struct {
    Read Read `long:"read" short:"" help:"reads a file"`
}
type Read struct {
    FileName string `long:"--filename" short:"-f" help:"the name of the file to read"`
    SkipWhiteSpace bool `long:"--skip-white-space" short:"" help:"skips white spaces"`
}

Binding Behavior

When parsing a flag, Flaggy looks for an optional method called Run and invokes that method if it is available on the struct when the parsing process is finished. The Run method may also return error in case it encounters an error.

type Options struct {
    Read Read `long:"read" short:"" help:"reads a file"`
}
type Read struct {
    FileName string `long:"--filename" short:"-f" help:"the name of the file to read"`
    SkipWhiteSpace bool `long:"--skip-white-space" short:"" help:"skips white spaces"`
}
func (r Read) Run() error {
    failing := true
    if len(r.FileName) == 0 {
        failing = true
    }
    if failing {
        flaggy.PrintHelp()
        return fmt.Errorf("file name is not provided")
    }
    ...
    return nil
}

If the Run method returns an error, the Parse method will return it back.