)

// setOp parses the operation string (first argument).
func setOp(arg string) {
	// Recognize 'go tool pack grc' because that was the
	// formerly canonical way to build a new archive
	// from a set of input files. Accepting it keeps old
	// build systems working with both Go 1.2 and Go 1.3.
	if arg == "grc" {
		arg = "c"
	}

	for _, r := range arg {
		switch r {
		case 'c', 'p', 'r', 't', 'x':
			if op != 0 {