tomnomnom/gron · error

failed to parse '%s' as gron statement

Error message

failed to parse '%s' as gron statement

What it means

gronValues (the `--values`/`-v` action) parses each input line with statementFromString. If tokenization yields zero tokens, the line is not a recognizable gron statement and the action aborts with "failed to parse '%s' as gron statement" and exit code exitParseStatements.

Source

Thrown at main.go:423

	// Fprintf below
	j = bytes.TrimSpace(j)

	fmt.Fprintf(w, "%s\n", j)

	return exitOK, nil
}

// gronValues prints just the scalar values from some input gron statements
// without any quotes or anything of that sort; a bit like jq -r
// e.g. json[0].user.name = "Sam"; -> Sam
func gronValues(r io.Reader, w io.Writer, opts int) (int, error) {
	scanner := bufio.NewScanner(os.Stdin)

	for scanner.Scan() {
		s := statementFromString(scanner.Text())

		if len(s) == 0 {
			return exitParseStatements, fmt.Errorf("failed to parse '%s' as gron statement", scanner.Text())
		}

		// strip off the leading 'json' bare key
		if s[0].typ == typBare && s[0].text == "json" {
			s = s[1:]
		}

		// strip off the leading dots
		if s[0].typ == typDot || s[0].typ == typLBrace {
			s = s[1:]
		}

		for _, t := range s {
			switch t.typ {
			case typString:
				var text string
				err := json.Unmarshal([]byte(t.text), &text)
				if err != nil {

View on GitHub (pinned to 88a6234ea2)

Solutions

1. Ensure input to `gron --values` is gron-generated statement output, not raw JSON
2. Strip blank/empty lines before piping: grep -v '^[[:space:]]*$'
3. Sanitize any filter (grep/awk) output so it preserves complete `json... = value;` lines

Example fix

// before
$ echo '{"a":1}' | gron -v   // failed to parse '{"a":1}' as gron statement

// after
$ echo '{"a":1}' | gron | gron -v

grep -v '^[[:space:]]*$' gron_output | grep -E '^json.*= .*;$' | gron --values

code, err := gronValues(input, output, opts)
if err != nil {
	if strings.Contains(err.Error(), "failed to parse") {
		// sanitize input lines and retry
	}
	return err
}

When it happens

Trigger: `gron --values` given blank lines or lines without assignment structure (no `key = value;` form), e.g. raw JSON, log lines, or empty input lines from trailing newlines.

Common situations: Piping gron output through filters that insert blank lines or headers; forgetting to run `gron` first and passing JSON directly to `gron -v`; concatenating outputs with stray whitespace.

Understand the failure class

Background: "Unknown argument", "Invalid value", and "must be one of": invalid CLI argument errors explained — this error's family across 35 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• invalid JSON layout
• invalid statement
• statement has no value
• failed to form statements: %s
• non-assignment statement

AI-assisted analysis of tomnomnom/gron@88a6234ea2 (2026-09-06). Data as JSON: /api/errors/15537bf78c51e967. Report an issue: GitHub.