Implement command parsing (git style)

We can use stopAtFirstUnknown to parse an input argv array several times, making complex scenarios possible.

As an example we'll recreate the git merge command, which has this form.

$ git <command> [options]

Example

This is the full example script. After the first commandLineArgs() invocation, the _unknown list is used as input to the next invocation.

const commandLineArgs = require('command-line-args')

/* first - parse the main command */
const mainDefinitions = [
  { name: 'command', defaultOption: true }
]
const mainOptions = commandLineArgs(mainDefinitions, { stopAtFirstUnknown: true })
const argv = mainOptions._unknown || []

console.log('mainOptions\n===========')
console.log(mainOptions)

/* second - parse the merge command options */
if (mainOptions.command === 'merge') {
  const mergeDefinitions = [
    { name: 'squash', type: Boolean },
    { name: 'message', alias: 'm' }
  ]
  const mergeOptions = commandLineArgs(mergeDefinitions, { argv })

  console.log('\nmergeOptions\n============')
  console.log(mergeOptions)
}

This command produces the following output.

$ node example.js merge --squash -m "This is my commit message"
mainOptions
===========
{ _unknown: [ '--squash', '-m', 'This is my commit message' ],
  command: 'merge' }

mergeOptions
============
{ squash: true, message: 'This is my commit message' }