let Parser=require('command-line-arguments-parser');

let parserName=new Parser();

//the following are methods to specify rules

//to set default option for your command
parserName.setDefaultOption(option);
//to add options which are valid you need to pass value validator callback to validate value given to your option in this your should start with hyphen
parserName.addLegalOption(option1 ,value1ValidatorCallback);

//if your options doing same work you need to add replaces
parserName.addReplacer(key ,value); //example  ('-h','--help')

//if your option don't need value you need to add into LongNames
//it should start with double hyphen to make valid LongName
parserName.addLegalLongName('--'+yourLongNameName);


//to enable combined flags
parserName.enableCombinedFlags(); // example -abc 20 30 40 it will parse as -a20,-b30,-c40

//It helps to specify how many maximum options you can parse at a time
parserName.setMaximumOptions(number);
/* parser.setMaximumOptions(1);
your arguments -n  10 -c 20
 it will throw error maximum options reached
 */

 //pass an array of  things to parse method to get parsedArguments
 parserName.parse(args); //example let args =['-n','10','files'] for head

  let Parser=require('command-line-arguments-parser');

  let headParser = new Parser();
  //default option 'n'
  headParser.setDefaultOption('n');
  //two c and n options which take only number
  headParser.addLegalOption('-n',isItNumber);
  headParser.addLegalOption('-c',isItNumber);

  // -- and -n10 functionality are same
  headParser.addReplacer('--','-n10');

  // --help which don't need any input
  headParser.addLegalLongName('--help');

  //by default combined flags are false
  headParser.enableCombinedFlags();

  //maximum options set to 1
  headParser.setMaximumOptions(1);

  let isItNumber = function (value) {
    return (+value>0);
  };

  let args=['--help'];
  //output
  { arguments: [],
  LongNames: [ '--help' ],
  optionSetBy: 'default',
  flags: {},
  defaultOption: 'n' }

  args=['-n10','-c12'];
  //output
  Error:Maximum options reached

  args=['-n10',"toDo.txt"];
  //output
  {
    arguments:['toDo.txt'],
    LongNames:[],
    optionSetBy:'default',
    flags:{n:10},
    defaultOption:'n'
  }

  args=['-n12',"toDo.txt",'--help'];//once it see argument remaining everything is argument
  //output
  {
    arguments:['toDo.txt','--help'],
    LongNames:[],
    optionSetBy:'default',
    flags:{n:12},
    defaultOption:'n'
  }

  args=[];
  //output
  {
    arguments:[],
    LongNames:[],
    optionSetBy:'default',
    flags:{},
    defaultOption:'n'
  }

  args =['-10'];
  //output
  {
    arguments:[],
    LongNames:[],
    optionSetBy:'n',
    flags:{n:10},
    defaultOption:'n'
  }

//when args as below
args=['-n10','-20'];
//it will replace n value with 20 because default option is n
{
  arguments:[],
  LongNames:[],
  optionSetBy:'n',
  flags:{n:20},
  defaultOption:'n'
}