What causes "Only one of script or scripts can be specified." in hashicorp/packer?

Remove either the `script` or the `scripts` key from the provisioner block so only one remains.

Only one of script or scripts can be specified.

Error message

Only one of script or scripts can be specified.

What it means

This is a template-validation error thrown by the shell provisioner's Prepare() phase in Packer. The provisioner accepts two mutually exclusive ways to supply a script: the singular `script` field and the plural `scripts` list. If both are set in the same provisioner block, Prepare refuses to guess which one to use and returns this error before any build runs.

Source

Thrown at provisioner/shell/provisioner.go:152

		p.config.RemoteFile = fmt.Sprintf("script_%d.sh", rand.Intn(9999))
	}

	if p.config.RemotePath == "" {
		p.config.RemotePath = fmt.Sprintf("%s/%s", p.config.RemoteFolder, p.config.RemoteFile)
	}

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

	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))

View on GitHub (pinned to eb36e3c3e4)

Solutions

Remove either the `script` or the `scripts` key from the provisioner block so only one remains.
If you want multiple scripts, delete `script` and list every file in `scripts`.
If you only need one script, keep `script` and delete the `scripts` list.

Example fix

// before
provisioner "shell" {
  script  = "./setup.sh"
  scripts = ["./a.sh", "./b.sh"]
}
// after
provisioner "shell" {
  scripts = ["./a.sh", "./b.sh"]
}

Defensive patterns

Strategy: validation

Validate before calling

if cfg.Script != "" && len(cfg.Scripts) > 0 {
    return fmt.Errorf("provisioner config: set only one of script or scripts")
}

Prevention

Pick one canonical field per provisioner block; prefer `scripts` when in doubt.
Lint templates for coexisting `script` and `scripts` keys before `packer build`.
Validate early: call Provisioner.Prepare() in tests with your config instead of discovering it at build time.
When migrating single-script templates, delete the old `script` key in the same change.

When it happens

Trigger: Calling Prepare() with a config where p.config.Script is a non-empty string AND p.config.Scripts has length > 0 (e.g. HCL2/JSON template sets both `script = "a.sh"` and `scripts = ["b.sh"]` in the same shell provisioner block).

Common situations: Users migrating an old single-script template to a multi-script layout and leaving the old `script` key behind; copy-pasting a provisioner block that already had `scripts` and adding `script` for a quick test; SDK/plugin code programmatically populating both fields from overlapping template sections.

Related errors

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/3c2801e56bf9c442. Report an issue: GitHub.