`$ ls -la` to list files on unix. for success, call process.exit with zero

from.args.js

const n = [ 'error', 'stdout', 'stderr' ]
require('child_process').exec('ls -la', function output () {
  return []
    .slice
    .call ( arguments ) // or do [].from(arguments)
    .reduce ( ( p, c, i ) => {
      if ( c )
        console.log(`\n\n${n[i]}:\n\n${c}`)
      return p
    }, process.exit ) ( 0 )
})