cobra.js

A small cli framework for Deno. This is heavily inspired on the excellent Cobra. The framework relies on the Deno's built-in flags library for the parsing of arguments.

The foundation to a good cli is good help. Most of the complexity in Cobra.js is to auto-generate usage information. Cobra.js self-generates help from a command's configuration.

All clis in cobra.js will use commands and flags.

Commands

The basic configuration for a command, specifies the following:

export interface Cmd {
  use: string; // name and usage
  short?: string; // short description shown in help
  long?: string; // long help (cmd action --help)
  run: Run;
}

// import the library
import { cli } from "https://deno.land/x/cobra/mod.ts";

// create the root command
const root = cli({ use: "greeting (hello|goodbye) [--name name] [--strong]" });
root.addFlag({
  short: "s",
  name: "strong",
  type: "boolean",
  usage: "say message strongly",
  persistent: true,
});
// add a subcommand
const hello = root.addCommand({
  use: "hello --name string [--strong]",
  short: "says hello",
  // this is the handler for the command, you get
  // the command being executed, any args following a `--`
  // and an object to let you access relevant flags.
  run: (cmd, args, flags): Promise<number> => {
    const strong = (flags.value<boolean>("strong") ?? false) ? "!!!" : "";
    let n = flags.value<string>("name");
    n = n === "" ? "mystery person" : n;
    cmd.stdout(`hello ${n}${strong}`);
    return Promise.resolve(0);
  },
});

To execute the cli, simply root.execute() with arguments:

Deno.exit(await root.execute(Deno.args));

The return of the command is a Promise<number> which is a number you can use to provide to the Deno.exit(n) function.

Flags

The second component is flags. While parsing arguments can easily be one with utils such as [parse](from https://deno.land/std/flags) when creating cli tools, you'll also want to provide long/short flag names, the type of the data that you expect, and usage:

export interface Flag {
  type: "string" | "boolean" | "number";
  name: string;
  usage: string;
  short: string;
  required: boolean;
  persistent: boolean;
  changed: boolean;
  default: null | unknown | unknown[];
  value: null | unknown | unknown[];
}

Adding flags to the command above:

hello.addFlag({
  short: "n",
  name: "name",
  type: "string",
  usage: "name to say hello to",
});
hello.addFlag({
  short: "s",
  name: "strong",
  type: "boolean",
  usage: "say hello strongly",
});

Processing flags is similarly trivial:

const n = flags.value<string>("name");

The value returned will be the one entered by the user, or the specified default in the configuration for the default value for the type - "" or false or 0.

Flags marked as persistent can be associated with a container command and are available to all subcommands, reducing code duplication.

Running your commands

Once you build your command tree and related, flags, you simply call the root command's execute() with a list of arguments:

Deno.exit(await root.execute(Deno.args));

Help is built-in

Help is implemented as a persistent flag on the root command, simply passing -h or --help to any command, will display help. The help you get will be context sensitive. Container commands will list possible subcommands, and their persistent flags. A leaf command will show usage, flags and persistent flags.

This results in help that looks like this:

> deno run main.ts
greeting

Usage:
  greeting [commands]

Available Commands:
  goodbye   says goodbye
  hello     says hello

Flags:
  -h, --help   display greeting's help

> deno run main.ts hello -h
hello --name string [--strong]

Usage:
  hello --name string [--strong]

Flags:
  -h, --help     display greeting's help
  -n, --name     name to say hello to
  -s, --strong   say hello strongly