template needs to be specified in golang's text/template for

Error message

template needs to be specified in golang's text/template format.

What it means

Guard in TemplateFormat.TransformData: the TemplateFormat was constructed with an empty template string, so it cannot render output; the caller must supply a Go text/template before using this output format.

Source

Thrown at command/data_format.go:63

func (p *JSONFormat) TransformData(data any) (string, error) {
	var buf bytes.Buffer
	err := codec.NewEncoder(&buf, jsonHandlePretty).Encode(data)
	if err != nil {
		return "", err
	}

	return buf.String(), nil
}

type TemplateFormat struct {
	tmpl string
}

// TransformData returns template format string data.
func (p *TemplateFormat) TransformData(data any) (string, error) {
	var out bytes.Buffer
	if len(p.tmpl) == 0 {
		return "", fmt.Errorf("template needs to be specified in golang's text/template format.")
	}

	t, err := template.New("").Funcs(makeFuncMap()).Parse(p.tmpl)
	if err != nil {
		return "", err
	}

	err = t.Execute(&out, data)
	if err != nil {
		return "", err
	}
	return out.String(), nil
}

func Format(json bool, template string, data any) (string, error) {
	var format string
	if json && len(template) > 0 {
		return "", fmt.Errorf("Both json and template formatting are not allowed")

View on GitHub (pinned to 482b49bf1a)

Solutions

Supply a Go text/template string when selecting template format, e.g. -template '{{ .Name }}'.
Add a pre-check that the template flag is non-empty before choosing the template formatter.
Fix whatever default/env resolution is yielding an empty template value.
Fall back to json format when no template is provided.

Example fix

// before
f, _ := command.DataFormat("template", os.Getenv("OUT_TMPL")) // env empty
// after
tmpl := os.Getenv("OUT_TMPL")
if tmpl == "" { return errors.New("-template is required with format=template") }
f, err := command.DataFormat("template", tmpl)

Defensive patterns

Strategy: validation

Validate before calling

if len(tmpl) == 0 {
    return errors.New("template format requires a non-empty -template value")
}
if _, err := template.New("t").Parse(tmpl); err != nil {
    return fmt.Errorf("invalid template: %w", err)
}

Type guard

null

Try / catch

out, err := formatter.TransformData(data)
if err != nil {
    if strings.Contains(err.Error(), "template needs to be specified") {
        return "", errors.New("-template is required when format=template")
    }
    return "", err
}

Prevention

Require the -template flag when format=template (mark it required conditionally).
Pre-parse the template at startup to fail fast on empty or invalid templates.
Avoid empty-defaulted env vars for template values; fail loudly when unset.
Add a smoke test rendering sample data through the template.

When it happens

Trigger: Calling command.DataFormat("template", "") (empty tmpl) to get a TemplateFormat, then invoking TransformData on any data.

Common situations: Passing -format=template without also supplying -template; an environment variable or config default that resolves to an empty string; template flag value trimmed to empty by upstream flag handling.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/9f6407d9f81e2644. Report an issue: GitHub.