What causes "%s" in OpenNHP/opennhp?

Run the command manually and inspect its stderr to see the actual message returned in the error

%s

Error message

%s

What it means

utils.Run executes an external command and captures stdout/stderr. If the command exits with an error it returns that error; if the command apparently succeeded but wrote anything to stderr, Run logs the stderr and fails the call with an error whose message is the raw stderr text (fmt.Errorf("%s", ...)). Any non-empty stderr is therefore treated as a failure even when the exit code was 0.

Solutions

Run the command manually and inspect its stderr to see the actual message returned in the error
Fix the invoked command/tool so it does not write to stderr on success (redirect its stderr to stdout or /dev/null in the wrapper script)
If the stderr output is benign and you control the code, check the error string or switch to calling cmd.Run() directly with your own exit-code-only policy

Example fix

// before (called via utils.Run, fails on any stderr)
out, _, err := utils.Run("tool", "arg")
// after (tolerate warnings, keep output)
cmd := exec.Command("tool", "arg")
var stderr bytes.Buffer
cmd.Stderr = &stderr
err := cmd.Run()
// inspect stderr only if err != nil

Defensive patterns

Strategy: validation

Validate before calling

var b bytes.Buffer
cmd := exec.Command("tool", "args")
cmd.Stderr = &b
if err := cmd.Run(); err != nil { return err }
if b.Len() > 0 { log.Printf("tool stderr: %s", b.String()) } // handle warnings explicitly before using utils.Run

Try / catch

out, cmdStr, err := utils.Run("tool", "arg")
if err != nil {
    log.Printf("command %s failed with stderr: %v", cmdStr, err)
    return err
}

Prevention

Test every wrapped command manually and check whether it writes to stderr on success
Silence or redirect benign stderr output in wrapper scripts (2>/dev/null) when success output is on stdout
Prefer checking exit codes over stderr content when wrapping third-party CLIs

When it happens

Trigger: A wrapped command writes warnings or informational messages to stderr while still producing correct stdout; or the command actually fails and cmd.Run() returns nil only in the exit-0-but-noisy case. The caller receives an error containing the tool's own stderr output as the message.

Common situations: CLI tools that print deprecation warnings or progress bars to stderr; scripts invoked by nhp that always emit a banner on stderr; tools whose success output partially goes to stderr.

Related errors

AI-assisted analysis of OpenNHP/opennhp@6e04ca5ff0 (2026-09-07). Data as JSON: /api/errors/f586379b5a4f0804. Report an issue: GitHub.

Appendix: source

Thrown at nhp/utils/cmd.go:33

	defer cancel()
	c := make(chan string)
	defer close(c)
	var stderr bytes.Buffer
	var stdout bytes.Buffer

	cmd := exec.CommandContext(ctx, command, args...) //nolint:gosec // G204: Command args passed as separate parameters, not shell string
	cmd.Stderr = &stderr
	cmd.Stdout = &stdout
	if len(in) > 0 {
		cmd.Stdin = strings.NewReader(in)
	}
	err := cmd.Run()
	if err != nil {
		return "", cmd.String(), err
	}
	if stderr.String() != "" {
		log.Println(stderr.String())
		return "", cmd.String(), fmt.Errorf("%s", stderr.String())
	}

	res := strings.Replace(stdout.String(), "\n", "", -1)
	return res, cmd.String(), nil
}

View on GitHub (pinned to 6e04ca5ff0)