alibaba/arthas · warning · IllegalArgumentException

The --line option is required unless --list-lines is used.

Error message

The --line option is required unless --list-lines is used.

What it means

Thrown as IllegalArgumentException by LineCommand.parseLines when lineSpecs is null or empty. parseLines expects at least one line spec; the only way to legally omit --line is to use --list-lines instead. This guard enforces that contract: you must either give explicit line numbers or ask to list them.

Source

Thrown at core/src/main/java/com/taobao/arthas/core/command/monitor200/LineCommand.java:274

        if (expand == null || expand < 0 || expand > ObjectView.MAX_DEEP) {
            return "expand must be between 0 and " + ObjectView.MAX_DEEP + ".";
        }
        String sizeLimitError = WatchCommand.validateSizeLimit(sizeLimit);
        if (sizeLimitError != null) {
            return sizeLimitError;
        }
        if (numberOfLimit <= 0) {
            return "limits must be greater than 0.";
        }
        if (stackDepth <= 0 || stackDepth > MAX_STACK_DEPTH) {
            return "stack-depth must be between 1 and " + MAX_STACK_DEPTH + ".";
        }
        return null;
    }

    static Set<Integer> parseLines(List<String> lineSpecs) {
        if (lineSpecs == null || lineSpecs.isEmpty()) {
            throw new IllegalArgumentException("The --line option is required unless --list-lines is used.");
        }
        Set<Integer> result = new LinkedHashSet<Integer>();
        for (String lineSpec : lineSpecs) {
            if (StringUtils.isEmpty(lineSpec)) {
                continue;
            }
            String[] parts = lineSpec.split(",");
            for (String part : parts) {
                String value = part.trim();
                if (value.length() == 0) {
                    continue;
                }
                if (value.indexOf('-') >= 0) {
                    throw new IllegalArgumentException("Line range syntax is not supported in the first version: "
                            + value);
                }
                final int lineNumber;
                try {

View on GitHub (pinned to 21cf2e9ba5)

Solutions

1. Add --line <numbers> (e.g. --line 42 or --line 10,20,30).
2. Or add --list-lines to enumerate available lines instead of targeting one.

Example fix

// before
line com.example.Foo

// after
line com.example.Foo --line 42
// or
line com.example.Foo --list-lines

boolean hasLine = lineSpecs != null && !lineSpecs.isEmpty();
if (!hasLine && !listLinesFlag) {
    // require either --line or --list-lines before invoking the command
}

static boolean hasLineInput(List<String> specs, boolean listLines) {
    return listLines || (specs != null && !specs.isEmpty());
}

try { Set<Integer> lines = LineCommand.parseLines(lineSpecs); } catch (IllegalArgumentException e) { // prompt: add --line N or --list-lines }

When it happens

Trigger: Run the line command without --line and without --list-lines, so the line-spec collection passed to parseLines is null/empty. The command cannot proceed because there is no target line to set a breakpoint/inspection on and listing was not requested.

Common situations: User forgets --line; assumes a default line is picked; misreads the help and provides neither --line nor --list-lines.

Related errors

• '{s}' is not a valid size. Should be numeric value followed
• '{s}' is not a valid timespan. Shoule be numeric value follo
• {optionName} must not be blank.
• {optionName} must be greater than 0.
• {optionName} is invalid: {value}

AI-assisted analysis of alibaba/arthas@21cf2e9ba5 (2026-08-14). Data as JSON: /api/errors/430ff6b678e18e42. Report an issue: GitHub.