What causes "invalid null string in 'scripts'" in hashicorp/terraform?

Filter nulls out of the inline list, e.g. inline = [for c in var.commands : c if c != null].

invalid null string in 'scripts'

Error message

invalid null string in 'scripts'

What it means

Error from generateScripts() while iterating the 'inline' list of the remote-exec provisioner: a list element is null (cty.NullVal). Each inline entry must be a non-null string.

Source

Thrown at internal/builtin/provisioners/remote-exec/resource_provisioner.go:158

	return resp
}

func (p *provisioner) Stop() error {
	p.cancel()
	return nil
}

func (p *provisioner) Close() error {
	return nil
}

// generateScripts takes the configuration and creates a script from each inline config
func generateScripts(inline cty.Value) ([]string, error) {
	var lines []string
	for _, l := range inline.AsValueSlice() {
		if l.IsNull() {
			return nil, errors.New("invalid null string in 'scripts'")
		}

		s := l.AsString()
		if s == "" {
			return nil, errors.New("invalid empty string in 'scripts'")
		}
		lines = append(lines, s)
	}
	lines = append(lines, "")

	return []string{strings.Join(lines, "\n")}, nil
}

// collectScripts is used to collect all the scripts we need
// to execute in preparation for copying them.
func collectScripts(v cty.Value) ([]io.ReadCloser, error) {
	// Check if inline
	if inline := v.GetAttr("inline"); !inline.IsNull() {

View on GitHub (pinned to c9def3e214)

Solutions

Filter nulls out of the inline list, e.g. inline = [for c in var.commands : c if c != null].
Ensure every element of the list variable is a concrete string.

Example fix

// before
variable "commands" { type = list(string) }
provisioner "remote-exec" {
  inline = var.commands
}
// after
provisioner "remote-exec" {
  inline = [for c in var.commands : c if c != null]
}

Defensive patterns

Strategy: validation

Validate before calling

# Strip null entries from inline before passing to the provisioner:
# inline = [for c in var.commands : c if c != null]
# Or type the variable so nulls cannot enter:
variable "commands" { type = list(string) }

Prevention

Type list variables as list(string), not list(any).
Apply compact()/filter to drop nulls from generated lists.
Validate module inputs with terraform validate in CI.

When it happens

Trigger: provisioner "remote-exec" { inline = ["echo hi", null] } — a null element, commonly produced by a list variable containing a null item.

Common situations: A variable like var.commands that includes a null element (e.g. conditional that yields null); compact() not applied to a sparse list.

Related errors

AI-assisted analysis of hashicorp/terraform@c9def3e214 (2026-08-07). Data as JSON: /api/errors/5e8866169084871e. Report an issue: GitHub.