Commands and Sub-commands ========================= The base `Command` interface is found in `cmd/cmd.go`. Commands need to provide an `Info` method that returns an Info struct. The info struct contains: name, args, purpose and a detailed description. This information is used to provide the default help for the command. In the same package, there is `CommandBase` whose purpose is to be composed into new commands, and provides a default no-op SetFlags implementation, a default Init method that checks for no extra args, and a default Help method. Supercommands ============= `Supercommand`s are commands that do many things, and have "sub-commands" that provide this functionality. Git and Bazaar are common examples of "supercommands". Subcommands must also provide the `Command` interface, and are registered using the `Register` method. The name and aliases are registered with the supercommand. If there is a duplicate name registered, the whole thing panics. Supercommands need to be created with the `NewSuperCommand` function in order to provide a fully constructed object. The 'help' subcommand --------------------- All supercommand instances get a help command. This provides the basic help functionality to get all the registered commands, with the addition of also being able to provide non-command help topics which can be added. Help topics have a `name` which is what is matched from the command line, a `short` one line description that is shown when ` help` is called, and a `long` text that is output when the topic is requested. Execution ========= The `Main` method in the cmd package handles the execution of a command. A new `gnuflag.FlagSet` is created and passed to the command in `SetFlags`. This is for the command to register the flags that it knows how to handle. The args are then parsed, and passed through to the `Init` method for the command to decide what to do with the positional arguments. The command is then `Run` and passed in an execution `Context` that defines the standard input and output streams, and has the current working directory.