shlex

var Posix = Dialect{
	IsSpace: func(r rune) bool {
		return ' ' == r || '\t' == r || '\n' == r
	},
	IsQuote: func(r rune) bool {
		return '"' == r || '\'' == r
	},
	Escape: func(s rune, r, r0 rune) rune {
		if '\\' != r {
			return NoEscape
		}
		switch s {
		case Space, Word:
			if '\n' == r0 || EmptyRune == r0 {
				return EmptyRune
			}
			return r0
		case DoubleQuote:
			if '\n' == r0 || EmptyRune == r0 {
				return EmptyRune
			}
			if '$' == r0 || '`' == r0 || '"' == r0 || '\\' == r0 {
				return r0
			}
			return NoEscape
		default:
			return NoEscape
		}
	},
}

var Windows = Dialect{
	IsSpace: func(r rune) bool {
		return ' ' == r || '\t' == r || '\r' == r || '\n' == r
	},
	IsQuote: func(r rune) bool {
		return '"' == r
	},
	Escape: func(s rune, r, r0 rune) rune {
		switch s {
		case Space, Word:
			if '\\' == r && '"' == r0 {
				return r0
			}
			return NoEscape
		case DoubleQuote:
			if ('\\' == r || '"' == r) && '"' == r0 {
				return r0
			}
			return NoEscape
		default:
			return NoEscape
		}
	},
	LongEscape: func(s rune, r rune, line string) ([]rune, string, rune, int) {

		if '\\' != r {
			return nil, "", 0, 0
		}

		var w int
		n := 0
		for {
			r, w = utf8.DecodeRuneInString(line[n:])
			n++
			if 0 == w || '\\' != r {
				break
			}
		}

		if 2 > n {
			return nil, "", 0, 0
		}

		if '"' != r {
			return []rune(strings.Repeat("\\", n-1)), line[n-1:], r, w
		} else if 0 == n&1 {
			return []rune(strings.Repeat("\\", n/2-1)), line[n-1:], '"', 1
		} else {
			return []rune(strings.Repeat("\\", n/2-1)), line[n-2:], '\\', 1
		}
	},
}