ory/hydra · warning

unable to print to stdout

Error message

unable to print to stdout

What it means

AskScannerForConfirmation prints a yes/no prompt to stdout in a loop. If the Fprintf to stdout fails (broken pipe, closed stdout), the interactive confirmation cannot proceed and the write error is wrapped with this message, returning false.

Source

Thrown at oryx/cmdx/user_input.go:42

	}

	ok, err := AskScannerForConfirmation(s, bufio.NewReader(stdin), stdout)
	if err != nil {
		Must(err, "Unable to confirm: %s", err)
	}

	return ok
}

func AskScannerForConfirmation(s string, reader *bufio.Reader, stdout io.Writer) (bool, error) {
	if stdout == nil {
		stdout = os.Stdout
	}

	for {
		_, err := fmt.Fprintf(stdout, "%s [y/n]: ", s)
		if err != nil {
			return false, errors.Wrap(err, "unable to print to stdout")
		}

		response, err := reader.ReadString('\n')
		if err != nil {
			return false, errors.Wrap(err, "unable to read from stdin")
		}

		response = strings.ToLower(strings.TrimSpace(response))
		if response == "y" || response == "yes" {
			return true, nil
		} else if response == "n" || response == "no" {
			return false, nil
		}
	}
}

View on GitHub (pinned to 4174065ffb)

Solutions

1. Ensure stdout is writable before prompting — run the command with a valid terminal or redirect stdout to a file
2. Avoid piping the interactive command into tools that exit early (e.g. `| head`) — use `--yes`/non-interactive flags if available
3. Check for a non-interactive mode or pre-answer flag in the CLI to skip confirmation entirely
4. Handle the returned error in your wrapper and fall back to explicit confirmation logic

Example fix

// before
$ oryx dangerous-cmd | head -1   # stdout closes -> prompt write fails
// after
$ oryx dangerous-cmd --yes       # or run without the broken pipe

if fi, err := os.Stdout.Stat(); err != nil || fi == nil {
    return fmt.Errorf("stdout unavailable; use a non-interactive mode")
}

ok, err := cmdx.AskForConfirmation("Proceed?")
if err != nil {
    log.WithError(err).Warn("cannot prompt; aborting interactive confirmation")
    return errInteractiveUnavailable
}

When it happens

Trigger: Calling AskForConfirmation (via AskScannerForConfirmation) in an environment where stdout is closed or broken — e.g. piping output to a closed consumer, running headless/CI with stdout redirected to a dead descriptor.

Common situations: Running interactive CLIs in CI where stdout is `head`-truncated (SIGPIPE); scripts closing fd 1; containers without a working TTY/stdout.

Related errors

• unable to read from stdin
• failed to write json output
• command expects one argument which is the path to the output
• A DSN is required as a positional argument when not passing
• Janitor requires at least one of --tokens, --requests or --g

AI-assisted analysis of ory/hydra@4174065ffb (2026-09-03). Data as JSON: /api/errors/ab770041613032fa. Report an issue: GitHub.