Either a script file or inline script must be specified.

Error message

Either a script file or inline script must be specified.

What it means

Thrown by the shell provisioner's Prepare() when neither a script file nor inline commands were provided. The provisioner needs something to execute on the machine; with an empty `scripts` list and a nil `inline` field there is no work to do, so validation fails early with this error.

Source

Thrown at provisioner/shell/provisioner.go:161

	}

	if p.config.Vars == nil {
		p.config.Vars = make([]string, 0)
	}

	var errs *packersdk.MultiError
	if p.config.Script != "" && len(p.config.Scripts) > 0 {
		errs = packersdk.MultiErrorAppend(errs,
			errors.New("Only one of script or scripts can be specified."))
	}

	if p.config.Script != "" {
		p.config.Scripts = []string{p.config.Script}
	}

	if len(p.config.Scripts) == 0 && p.config.Inline == nil {
		errs = packersdk.MultiErrorAppend(errs,
			errors.New("Either a script file or inline script must be specified."))
	} else if len(p.config.Scripts) > 0 && p.config.Inline != nil {
		errs = packersdk.MultiErrorAppend(errs,
			errors.New("Only a script file or an inline script can be specified, not both."))
	}

	for _, path := range p.config.Scripts {
		if _, err := os.Stat(path); err != nil {
			errs = packersdk.MultiErrorAppend(errs,
				fmt.Errorf("Bad script '%s': %s", path, err))
		}
	}

	// Do a check for bad environment variables, such as '=foo', 'foobar'
	for _, kv := range p.config.Vars {
		vs := strings.SplitN(kv, "=", 2)
		if len(vs) != 2 || vs[0] == "" {
			errs = packersdk.MultiErrorAppend(errs,
				fmt.Errorf("Environment variable not in format 'key=value': %s", kv))

View on GitHub (pinned to eb36e3c3e4)

Solutions

Add `inline = ["echo hello"]` for ad-hoc commands.
Add `scripts = ["./myscript.sh"]` (or `script = "./myscript.sh"`) to point at a script file.
If the block is unused scaffolding, remove the shell provisioner block entirely.

Example fix

// before
provisioner "shell" {}
// after
provisioner "shell" {
  inline = ["echo hello"]
}

Defensive patterns

Strategy: validation

Validate before calling

if len(cfg.Scripts) == 0 && cfg.Inline == nil {
    return fmt.Errorf("provisioner config: must set scripts, script, or inline")
}

Prevention

Always pair a shell provisioner block with at least one command source.
Check that template variables feeding `script` have non-empty defaults.
Treat an empty provisioner block as a template error and remove scaffolding.
Add a unit test calling Prepare() with your real config to catch it in CI.

When it happens

Trigger: Prepare() is called with len(p.config.Scripts) == 0 and p.config.Inline == nil — i.e. the provisioner block contains neither `script`/`scripts` nor `inline`. Also occurs when a configured `script` path is empty or the whole block was left without execution content.

Common situations: Empty shell provisioner block left as scaffolding (`provisioner "shell" {}`); template variable interpolation resolving to an empty string so `script` becomes ""; users setting only env_vars/useful keys but forgetting to specify what to run.

Understand the failure class

Background: "X is required", "must be set", "cannot be empty": the missing-required-config error family, from Vertex AI project/location to WeChat keys — this error's family across 18 libraries.

Related errors

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/dfdc4a6917cd64d3. Report an issue: GitHub.