apple/pkl · error · CliException

Output file `$outputFile` is a directory. Did you mean `--mu

Error message

Output file `$outputFile` is a directory. Did you mean `--multiple-file-output-path`?

What it means

In single-file output mode, CliEvaluator.writeOutput checks whether the target output path is an existing directory before writing; if so it throws this error and hints that the user probably intended multiple-file output mode. This happens because evaluating `output.files` output into a single output path doesn't make sense.

Source

Thrown at pkl-cli/src/main/kotlin/org/pkl/cli/CliEvaluator.kt:167

    return evaluateExpressionString(moduleSource, options.expression)
      .toByteArray(StandardCharsets.UTF_8)
  }

  /** Renders each module's `output.bytes`, writing it to the specified output file. */
  private fun writeOutput(builder: EvaluatorBuilder) {
    val evaluator = builder.setOutputFormat(options.outputFormat).build()
    evaluator.use { ev ->
      val outputFiles = fileOutputPaths
      if (outputFiles != null) {
        // files that we've written non-empty output to
        // YamlRenderer produces empty output if `isStream` is true and `output.value` is empty
        // collection
        val writtenFiles = mutableSetOf<Path>()

        for ((moduleUri, outputFile) in outputFiles) {
          val moduleSource = toModuleSource(moduleUri, inputStream)
          if (Files.isDirectory(outputFile)) {
            throw CliException(
              "Output file `$outputFile` is a directory. " +
                "Did you mean `--multiple-file-output-path`?"
            )
          }
          val output = ev.evalOutput(moduleSource)
          outputFile.createParentDirectories()
          if (!writtenFiles.contains(outputFile)) {
            // write file even if output is empty to overwrite output from previous runs
            outputFile.writeBytes(output)
            if (output.isNotEmpty()) {
              writtenFiles.add(outputFile)
            }
          } else {
            if (output.isNotEmpty()) {
              outputFile.writeString(
                options.moduleOutputSeparator + '\n',
                Charsets.UTF_8,
                StandardOpenOption.WRITE,

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. If you intended multiple-file output, use `--multiple-file-output-path` instead.
2. Otherwise, specify a file path (not an existing directory) as the output, or delete/rename the directory.
3. Fix shell scripts to pass a concrete file path for single-file output.
4. Clean output directories between runs.

Example fix

# before
$ pkl eval mymod.pkl out/   # out/ is a directory
# after
$ pkl eval mymod.pkl --multiple-file-output-path out/

import java.nio.file.Files
import java.nio.file.Path
require(!Files.isDirectory(Path.of(outputFile))) { "Output path $outputFile is a directory; use --multiple-file-output-path" }

try {
  ev.writeOutput(...)
} catch (e: CliException) {
  if (e.message?.contains("multiple-file-output-path") == true) {
    // rerun with --multiple-file-output-path
  }
}

When it happens

Trigger: Running a command whose evaluated output is written to a path that already exists as a directory — e.g. passing a directory to the plain output path argument, or re-running against a directory produced by a previous --multiple-file-output-path run.

Common situations: Mixing single-file and multiple-file output invocations on the same path; typos in the output path argument (pointing at a directory instead of a file); shell scripts that pass $OUTPUT_DIR where a file is expected.

Related errors

• Output path `$outputDir` exists and is not a directory.
• Output path `$outputDir` exists and is not a directory.
• Output file conflict: `output.files` entries `"${previousOut
• Output file conflict: `output.files` entry `"$pathSpec"` res
• Cannot substitute output path placeholder `%{moduleDir}` bec

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/c745a4dcedde43f3. Report an issue: GitHub.