# README

Simple and complete API for building command line applications in Go

Module cli provides a simple, fast and complete API for building command line applications in Go. In contrast to other libraries the emphasis is put on the definition and validation of positional arguments, handling of options from all levels in a single block as well as a minimalistic set of dependencies.

The core of the module is the command, option and argument parsing logic. After a successful parsing the command action is evaluated passing a slice of (validated) positional arguments and a map of (validated) options. No more no less.

Definition

co := cli.NewCommand("checkout", "checkout a branch or revision").
  WithShortcut("co").
  WithArg(cli.NewArg("revision", "branch or revision to checkout")).
  WithOption(cli.NewOption("branch", "Create branch if missing").WithChar('b').WithType(cli.TypeBool)).
  WithOption(cli.NewOption("upstream", "Set upstream for the branch").WithChar('u').WithType(cli.TypeBool)).
  WithAction(func(args []string, options map[string]string) int {
    // do something
    return 0
  })

add := cli.NewCommand("add", "add a remote").
  WithArg(cli.NewArg("remote", "remote to add")).

rmt := cli.NewCommand("remote", "Work with git remotes").
  WithCommand(add)

app := cli.New("git tool").
  WithOption(cli.NewOption("verbose", "Verbose execution").WithChar('v').WithType(cli.TypeBool)).
  WithCommand(co).
  WithCommand(rmt)
  // no action attached, just print usage when executed

os.Exit(app.Run(os.Args, os.Stdout))

Execution

Given the above definition is for a git client, e.g. gitc, running gitc with no arguments or with -h will produce (the exit code will be 1 in the former case, because the action is missing, and 0 in the latter, because help explicitly requested):

gitc [--verbose]

Description:
    git tool

Options:
    -v, --verbose   Verbose execution

Sub-commands:
    git checkout    checkout a branch or revision
    git remote      Work with git remotes

Running gitc with arguments matching e.g. the checkout definition, gitc co -vbu dev or gitc checkout -v --branch -u dev will execute the command as expected. Running into a parsing error, e.g. by providing an unknown option gitc co -f dev, will output a parsing error and a short usage string:

fatal: unknown flag -f
usage: gitc checkout [--verbose] [--branch] [--upstream] <revision>

License and copyright

Copyright (c) 2017. Oleg Sklyar and teris.io. MIT license applies. All rights reserved.

# Functions

New

New creates a new CLI App.

NewArg

NewArg creates a new positional argument.

NewCommand

NewCommand creates a new command to be added to an application or to another command.

NewOption

NewOption creates a new option with a given key and description.

Parse

Parse parses the original application arguments into the command invocation path (application -> first level command -> second level command etc.), a list of validated positional arguments matching the command being invoked (the last one in the invocation path) and a map of validated options matching one of the invocation path elements, from the top application down to the command being invoked.

Usage

Usage prints out the complete usage string.