options-env.js

#!/usr/bin/env node
// const { Command, Option } = require('commander'); // (normal include)
const { Command, Option } = require('../'); // include commander in git clone of commander repo
const program = new Command();

program.addOption(new Option('-p, --port <number>', 'specify port number')
  .default(80)
  .env('PORT')
);
program.addOption(new Option('-c, --colour', 'turn on colour output')
  .env('COLOUR')
);
program.addOption(new Option('-C, --no-colour', 'turn off colour output')
  .env('NO_COLOUR')
);
program.addOption(new Option('-s, --size <type>', 'specify size of drink')
  .choices(['small', 'medium', 'large'])
  .env('SIZE')
);

program.parse();
console.log(program.opts());

// Try the following:
//    node options-env.js --help
//
//    node options-env.js
//    PORT=9001 node options-env.js
//    PORT=9001 node options-env.js --port 123
//
//    COLOUR= node options-env.js
//    COLOUR= node options-env.js --no-colour
//    NO_COLOUR= node options-env.js
//    NO_COLOUR= node options-env.js --colour
//
//    SIZE=small node options-env.js
//    SIZE=enormous node options-env.js
//    SIZE=enormous node options-env.js --size=large