golang/go · error

invalid newline in =... value

Error message

invalid newline in %s=... value

What it means

Returned by checkEnvWrite when the value written via `go env -w` contains any vertical tab, carriage return, or newline (\v \r \n). The go env config file is one line per entry, so embedded newlines would corrupt the file structure.

Solutions

1. Trim trailing newlines from command substitution: assign then strip, or use `${var%$'\n'}`.
2. Reject multiline values at your config layer with strings.ContainsAny(v, "\v\r\n").
3. Use single-line equivalents (e.g. semicolons instead of newlines in compiler flags).

Example fix

# before
$ go env -w GOPROXY=$(printf 'a\nb')
error: invalid newline in GOPROXY=... value
# after — strip newlines first
$ go env -w GOPROXY=$(printf 'a\nb' | tr -d '\r\n')

import "strings"

if strings.ContainsAny(val, "\v\r\n") {
    return fmt.Errorf("value for %s contains newlines", key)
}

When it happens

Trigger: Any `go env -w KEY=...` value containing \v, \r, or \n — typically multiline text pasted from a terminal, or values captured from `$(cmd)` whose output ends in a newline.

Common situations: Pasting multiline strings; command substitution that includes trailing newlines; copy-paste from documentation with line breaks; values containing Windows CRLF line endings.

Related errors

• invalid NUL in =... value
• GOMODCACHE entry is relative; must be absolute path
• GOPATH entry cannot start with shell metacharacter '~
• GOPATH entry is relative; must be absolute path
• invalid

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/b24b3911a8ae016a. Report an issue: GitHub.

Appendix: source

Thrown at src/cmd/go/internal/envcmd/env.go:700

		if err != nil {
			return fmt.Errorf("invalid %s: %v", key, err)
		}
		if len(args) == 0 {
			return fmt.Errorf("%s entry cannot contain only space", key)
		}
		if !filepath.IsAbs(args[0]) && args[0] != filepath.Base(args[0]) {
			return fmt.Errorf("%s entry is relative; must be absolute path: %q", key, args[0])
		}
	}

	if !utf8.ValidString(val) {
		return fmt.Errorf("invalid UTF-8 in %s=... value", key)
	}
	if strings.Contains(val, "\x00") {
		return fmt.Errorf("invalid NUL in %s=... value", key)
	}
	if strings.ContainsAny(val, "\v\r\n") {
		return fmt.Errorf("invalid newline in %s=... value", key)
	}
	return nil
}

func readEnvFileLines(mustExist bool) []string {
	file, _, err := cfg.EnvFile()
	if file == "" {
		if mustExist {
			base.Fatalf("go: cannot find go env config: %v", err)
		}
		return nil
	}
	data, err := os.ReadFile(file)
	if err != nil && (!os.IsNotExist(err) || mustExist) {
		base.Fatalf("go: reading go env config: %v", err)
	}
	lines := strings.SplitAfter(string(data), "\n")
	if lines[len(lines)-1] == "" {

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