golang/go · error

missing =<value> in <pattern>=<value>

Error message

missing =<value> in <pattern>=<value>

What it means

Per-package flags (-gcflags, -ldflags, -asmflags, -gccgoflags) use a <pattern>=<flags> syntax when the value does not start with a dash. This error fires when the value contains no '=' character at all, making it impossible to separate the package pattern from the flags. The PerPackageFlag.set method checks for '=' via strings.Index and finds none.

Source

Thrown at src/cmd/go/internal/load/flag.go:58

}

// set is the implementation of Set, taking a cwd (current working directory) for easier testing.
func (f *PerPackageFlag) set(v, cwd string) error {
	f.raw = v
	f.present = true
	match := func(_ *modload.Loader, p *Package) bool { return p.Internal.CmdlinePkg || p.Internal.CmdlineFiles } // default predicate with no pattern
	// For backwards compatibility with earlier flag splitting, ignore spaces around flags.
	v = strings.TrimSpace(v)
	if v == "" {
		// Special case: -gcflags="" means no flags for command-line arguments
		// (overrides previous -gcflags="-whatever").
		f.values = append(f.values, ppfValue{match, []string{}})
		return nil
	}
	if !strings.HasPrefix(v, "-") {
		i := strings.Index(v, "=")
		if i < 0 {
			return fmt.Errorf("missing =<value> in <pattern>=<value>")
		}
		if i == 0 {
			return fmt.Errorf("missing <pattern> in <pattern>=<value>")
		}
		if v[0] == '\'' || v[0] == '"' {
			return fmt.Errorf("parameter may not start with quote character %c", v[0])
		}
		pattern := strings.TrimSpace(v[:i])
		match = MatchPackage(pattern, cwd)
		v = v[i+1:]
	}
	flags, err := quoted.Split(v)
	if err != nil {
		return err
	}
	if flags == nil {
		flags = []string{}
	}

View on GitHub (pinned to b6b368adc5)

Solutions

1. If you want flags applied to the packages on the command line, prefix the value with '-': go build -gcflags="-N -l".
2. If you want flags for a specific package pattern, use <pattern>=<flags>: go build -gcflags="runtime=-N -l".
3. For all packages in your module: go build -gcflags="./...=-N -l".

Example fix

// before — no = sign, no leading -
go build -gcflags=.
// after — flags with leading - apply to command-line packages
go build -gcflags="-N -l"
// or — pattern=value syntax
go build -gcflags="./...=-N -l"

// Validate per-package flag syntax before passing to go build.
func validatePerPackageFlag(v string) error {
    v = strings.TrimSpace(v)
    if v == "" || strings.HasPrefix(v, "-") {
        return nil // valid: empty or flags-only form
    }
    if !strings.Contains(v, "=") {
        return fmt.Errorf("missing =<value> in <pattern>=<value>: %q", v)
    }
    return nil
}

When it happens

Trigger: Passing -gcflags=. or -ldflags=myproject — a value that doesn't start with '-' and has no '='. The parser expects either -gcflags="-N -l" (flags apply to command-line packages) or -gcflags="./...=-N -l" (pattern=value syntax).

Common situations: Confusing the flag syntax — forgetting the '=' between pattern and flags. Migrating from older Go versions with different flag handling conventions. Shell quoting issues that strip the '='. Typing a bare pattern or package name without flags.

Related errors

• missing <pattern> in <pattern>=<value>
• parameter may not start with quote character %c
• missing key=value
• total length of command line and environment variables excee
• parse error

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/d9e285a69efdefe0. Report an issue: GitHub.