Clo (Command line objectives)

Clo is a Golang module to build declarations of a command-line app objectives - commands and arguments with values. Clo processes user provided command-line app input string (args) and returns a structured Request object. Clo takes care of a help command (perhaps more in the future).

Using clo in your app

While clo has been designed with Go 1.16 embedding in mind, we'll provide directions on how to use it today and will update once 1.16 is released.

Using clo module

• Run go get github.com/boggydigital/clo
• Import github.com/boggydgital/clo
• Create declarations in clo.json
• Load definitions using defs, _ := clo.LoadDefinitions("clo.json")
• Call clo.Parse(os.Args[1:], defs) to get a Request struct
• Route to app code using Request.Command and pass Request.Arguments

Here is an example of a main.go that implements this approach (NOTE: error handling is omitted for brevity)

package main

import (
	"github.com/boggydigital/clo"
	"{your-app-module}/cmd"
	"os"
)

func main() {
	defs, _ := clo.LoadDefinitions("clo.json")

	// Parse `os.Args` using definitions to get `Request` data
	req, _ := clo.Parse(os.Args[1:], defs)

	// Route request to app command handlers
	cmd.Route(req, defs)
}

Routing command requests and handling built-in commands

To route command-line objectives to app handlers you might add a cmd/route.go with a single Route func that routes arguments data to command handlers.

NOTE: In order to allow clo to handle built-in commands, in your Route handler you need to send nil and unknown commands to clo.Route.

Example:

package cmd

import (
	"github.com/boggydigital/clo"
)

func Route(req *clo.Request, defs *clo.Definitions) error {

	// allow clo to handle nil requests (this will show help by default)
	if req == nil {
		return clo.Route(nil, defs)
	}

	switch req.Command {
	case "yourCommand":
		// route yourCommand here
		// ...
	default:
		// allow clo to handle unknown commands
		return clo.Route(req, defs)
	}

	return nil
}

Getting values from a Request

Request provides few shortcuts to get values:

• ArgVal(arg string) - gets a single (first) value for an argument
• ArgValues(arg string) - gets all argument values specified in a Request
• Flag(arg string) - returns true is argument has been provided (with or without values)

Example:

package cmd

import (
	"github.com/boggydigital/clo"
)

func Route(req *clo.Request, defs *clo.Definitions) error {
	if req == nil {
		return clo.Route(nil, defs)
	}
	switch req.Command {
	case "validate":
		return Validate(req.ArgVal("path"), req.Flag("verbose"))
	default:
		return clo.Route(req, defs)
	}
}

where Validate is defined as:

package cmd

func Validate(path string, verbose bool) error { 
	
	// validate a file and display each test results if verbose was requested
	// ...
	
	return nil
}

Command-line objectives calling convention

App that uses clo would support the following calling convention:

app command [arguments [values]]

• Commands don't have any prefix. Commands can be specified by a prefix - the first command to match provided prefix would be used.
• Arguments are specified with - or -- prefixes. --debug is the same as -debug and, assuming there are no other arguments that start with d, it'll be the same as --d and -d
• Values are specified without any prefix.

Creating clo.json definitions

Clo.json has the following top-level properties:

• version - version of the definitions file, currently the only supported version is 1
• cmd - commands, arguments specified as a map:

{
  "cmd": {
    "validate": [
      "path",
      "verbose"
    ]
  }
}

• help - help messages specified for topics (topic is a : delimited list of command:argument):

{
  "help": {
    "clo": "command-line objectives",
    "validate": "validates that provided file doesn't have errors",
    "validate:path": "path to the file that should be validated",
    "validate:verbose": "print result of every validation test"
  }
}

Specifying argument values

Command arguments can also specify values supported by that argument. If values are specified for an argument, only those values would be considered valid and processing user input would stop when a different value is specified. Values are specified following a = sign:

{
  "cmd": {
    "command1": [
      "argument1=value1,value2",
      "argument2"
    ]
  }
}

In that declaration argument1 can only be specified with either value1 or value2, while argument2 can be specified with any arbitrary value.

Objectives attributes

To provide more control to authors clo supports several inline attributes that can be used to define constraints or set defaults:

• _ - default. Applies to command, attributes, values:

  • When specified on a command, this command will be used if no other command has been a match. Example: clo clo.json is the same as clo validate clo.json if validate_ command was specified as default.
  • When specified on an argument, this argument will be used if no other argument has been a match. Example: clo validate clo.json is the same as clo validate --path clo.json if path_ was specified as default.
  • When specified on a value, this argument value pair will be added to Request if the user didn't provide another value for that pair.

• ! - required. Applies to arguments. If set - argument value must be provided (can be in a form of default value). Example:

{
  "cmd": {
    "validate_": [
      "path_!"
    ]
  }
}

• ... - multiple. Applies to arguments. If set - argument can take more than one value. If not set - parsing multiple values for such argument would result in error.

• $ - env. variable. Applies to arguments. If set - argument value can be read from env. variable, unless specified by the user.