Command line parser utilizing a fancy RegExp to tokenize.

parser.js

module.exports = {
	Parser: function () {
		var self = this;

		self.parse = function (str) {
			var hash = {
				_: [],
				_flags: [],
				_trailing: ''
			};
			
			var quotedTrail = false;
			
			// https://regex101.com/r/dC5cB3
			var tokenizer = /(?:^| )((?:(?:-([a-z]+))|(?:--([a-z0-9]\w+)(?: (?:"((?:\\.|[^"\\])*)")|(?: (\w+)))?))|(?:"((?:\\.|[^"\\])*)")|(?:\w+))/ig;

			var match;
			while ((match = tokenizer.exec(str)) !== null) {
				if (match.index === tokenizer.lastIndex)
					tokenizer.lastIndex++;
				
				// Determine which pattern simply by checking which capture groups are undefined.
				if (match[3] === undefined && match[4] === undefined && match[5] === undefined) {
					// Single token or flagset.
					if (match[2] === undefined) {
						// Single token.
						if (match[6] === undefined) {
							// *** Single word.
							hash._.push(match[1]);
							
							if (!quotedTrail)
								hash._trailing += (hash._trailing.length ? ' ' : '') + match[1];
							else
								hash._trailing = match[1];
								
							quotedTrail = false;
						} else {
							// *** Quoted token.
							hash._.push(match[6]);
							hash._trailing = match[6];
							quotedTrail = true;
						}
					} else {
						// *** Flagset.
						for (var i = 0; i < match[2].length; i++) {
							hash._flags.push(match[2][i]);
							
							if (hash[match[2][i]] === undefined)
								hash[match[2][i]] = true;
							else if (typeof hash[match[2][i]] === 'boolean')
								hash[match[2][i]] = 2;
							else
								hash[match[2][i]]++;
								
							hash._trailing = '';
							quotedTrail = false;
						}
					}
				} else if (match[4] === undefined) {
					// *** Single word parameterized.
					hash[match[3]] = match[5];
					hash._trailing = match[5];
					quotedTrail = false;
				} else {
					// *** Quoted token parameterized.
					hash[match[3]] = match[4];
					hash._trailing = match[4];
					quotedTrail = true;
				}
			}
			
			return hash;

		};
	}
};