func appendBSBytes(b []byte, n int) []byte {
	for ; n > 0; n-- {
		b = append(b, '\\')
	}
	return b
}

// readNextArg splits command line string cmd into next
// argument and command line remainder.
func readNextArg(cmd string) (arg []byte, rest string) {
	var b []byte
	var inquote bool
	var nslash int
	for ; len(cmd) > 0; cmd = cmd[1:] {
		c := cmd[0]
		switch c {