golang/go · error

invalid %s value %q

Error message

invalid %s value %q

What it means

Returned by checkEnvWrite's value-validation switch when a key that only accepts enumerated values is given something outside the allowed set. Currently fires for GO111MODULE with values other than "", "auto", "on", "off".

Source

Thrown at src/cmd/go/internal/envcmd/env.go:664

	case "GOENV", "GODEBUG":
		return fmt.Errorf("%s can only be set using the OS environment", key)
	}

	// To catch typos and the like, check that we know the variable.
	// If it's already in the env file, we assume it's known.
	if !cfg.CanGetenv(key) {
		return fmt.Errorf("unknown go command variable %s", key)
	}

	// Some variables can only have one of a few valid values. If set to an
	// invalid value, the next cmd/go invocation might fail immediately,
	// even 'go env -w' itself.
	switch key {
	case "GO111MODULE":
		switch val {
		case "", "auto", "on", "off":
		default:
			return fmt.Errorf("invalid %s value %q", key, val)
		}
	case "GOPATH":
		if strings.HasPrefix(val, "~") {
			return fmt.Errorf("GOPATH entry cannot start with shell metacharacter '~': %q", val)
		}
		if !filepath.IsAbs(val) && val != "" {
			return fmt.Errorf("GOPATH entry is relative; must be absolute path: %q", val)
		}
	case "GOMODCACHE":
		if !filepath.IsAbs(val) && val != "" {
			return fmt.Errorf("GOMODCACHE entry is relative; must be absolute path: %q", val)
		}
	case "CC", "CXX":
		if val == "" {
			break
		}
		args, err := quoted.Split(val)
		if err != nil {

View on GitHub (pinned to b6b368adc5)

Solutions

1. Use one of the documented values: "", "auto", "on", or "off".
2. In module-aware Go (1.16+), prefer leaving GO111MODULE unset (defaults to on) rather than forcing a value.
3. If migrating from GOPATH mode, set GO111MODULE=on explicitly only while transitioning.

Example fix

# before
$ go env -w GO111MODULE=true
error: invalid GO111MODULE value "true"
# after
$ go env -w GO111MODULE=on

var go111Valid = map[string]bool{"": true, "auto": true, "on": true, "off": true}
if key == "GO111MODULE" && !go111Valid[val] {
    return fmt.Errorf("GO111MODULE must be one of '', auto, on, off; got %q", val)
}

When it happens

Trigger: `go env -w GO111MODULE=enable`, `go env -w GO111MODULE=yes`, `go env -w GO111MODULE=true`, or any value not in {"", auto, on, off}.

Common situations: Users assuming boolean syntax (true/false, yes/no, 1/0) for GO111MODULE; copy-paste from tutorials using non-canonical values; migration scripts that blindly forward old config.

Related errors

• %s cannot be modified
• %s can only be set using the OS environment
• unknown go command variable %s
• GOPATH entry cannot start with shell metacharacter '~': %q
• GOPATH entry is relative; must be absolute path: %q

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/2b57878d9168d7eb. Report an issue: GitHub.