stanfordnlp/CoreNLP · error · IllegalArgumentException

-output is required

Error message

-output is required

What it means

After flag parsing, main validates its required arguments; if -output was never provided it throws IllegalArgumentException("-output is required"). The tool needs an output path for the rewritten trees, so it refuses to run without one.

Solutions

1. Add -output <file> to the command line
2. Verify the flag is spelled -output exactly (case-insensitive match only)
3. Ensure no earlier parse error consumed the output path token

Example fix

// before
// java ParseAndSetLabels -parser model.ser.gz -labels labels.txt -sentences s.txt
// after
// java ParseAndSetLabels -parser model.ser.gz -labels labels.txt -sentences s.txt -output labeled.txt

if (!java.util.Arrays.asList(args).contains("-output")) throw new IllegalArgumentException("-output is required before running");

try {
  ParseAndSetLabels.main(args);
} catch (IllegalArgumentException e) {
  if ("-output is required".equals(e.getMessage())) System.err.println("Add -output <file> to the command line");
  throw e;
}

When it happens

Trigger: Running ParseAndSetLabels.main without the -output flag (or with a flag spelling that failed to match, leaving outputFile null).

Common situations: Forgotten -output in batch scripts; typo'd flag silently skipped by the unknown-argument check earlier; scripts migrated from other tools with different output flags.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Error: No dest file provided in properties or via command…
• Error: No training file provided in properties or via…
• Error: No training file provided in properties or via…
• Error: -train option must have treebankPath as first…
• -labels is required

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/b291b60e97446387. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/parser/tools/ParseAndSetLabels.java:240

      } else if (args[argIndex].equalsIgnoreCase("-binarize")) {
        binarize = true;
        argIndex += 1;
      } else if (args[argIndex].equalsIgnoreCase("-nobinarize")) {
        binarize = false;
        argIndex += 1;
      } else if (args[argIndex].equalsIgnoreCase("-useLabelKeys")) {
        useLabelKeys = true;
        argIndex += 1;
      } else if (args[argIndex].equalsIgnoreCase("-nouseLabelKeys")) {
        useLabelKeys = false;
        argIndex += 1;
      } else {
        throw new IllegalArgumentException("Unknown argument " + args[argIndex]);
      }
    }

    if (outputFile == null) {
      throw new IllegalArgumentException("-output is required");
    }
    if (sentencesFile == null && !useLabelKeys) {
      throw new IllegalArgumentException("-sentences or -useLabelKeys is required");
    }
    if (sentencesFile != null && useLabelKeys) {
      throw new IllegalArgumentException("Use only one of -sentences or -useLabelKeys");
    }
    if (labelsFile == null) {
      throw new IllegalArgumentException("-labels is required");
    }

    ParserGrammar parser = loadParser(parserFile, taggerFile);

    TreeBinarizer binarizer = null;
    if (binarize) {
      binarizer = TreeBinarizer.simpleTreeBinarizer(parser.getTLPParams().headFinder(), parser.treebankLanguagePack());
    }

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