bazelbuild/bazel · error · IOException

-cpuprofile <file> flag needs an argument

Error message

-cpuprofile <file> flag needs an argument

What it means

The Starlark interpreter CLI requires '-cpuprofile' to be immediately followed by a file path. If the flag is the last token on the command line, no profile output file is available and parsing aborts with this IOException.

Source

Thrown at src/main/java/net/starlark/java/cmd/Main.java:193

    // parse flags
    int i;
    for (i = 0; i < args.length; i++) {
      if (!args[i].startsWith("-")) {
        break;
      }
      if (args[i].equals("--")) {
        i++;
        break;
      }
      if (args[i].equals("-c")) {
        if (i + 1 == args.length) {
          throw new IOException("-c <cmd> flag needs an argument");
        }
        cmd = args[++i];
      } else if (args[i].equals("-cpuprofile")) {
        if (i + 1 == args.length) {
          throw new IOException("-cpuprofile <file> flag needs an argument");
        }
        cpuprofile = args[++i];
      } else {
        throw new IOException("unknown flag: " + args[i]);
      }
    }
    // positional arguments
    if (i < args.length) {
      if (i + 1 < args.length) {
        throw new IOException("too many positional arguments");
      }
      file = args[i];
    }

    if (cpuprofile != null) {
      FileOutputStream out = new FileOutputStream(cpuprofile);
      Starlark.startCpuProfile(out, Duration.ofMillis(10));
    }

View on GitHub (pinned to e6e199d060)

Solutions

1. Pass a path: `starlark -cpuprofile /tmp/cpu.prof script.star`.
2. Check the profile-path variable is non-empty before building the command line.
3. Ensure the path does not start with '-' (or use './-name').

Example fix

# before
starlark -cpuprofile

# after
starlark -cpuprofile /tmp/cpu.prof script.star

PROFILE="${PROFILE:-/tmp/cpu.prof}"  # default instead of empty
[ -n "$PROFILE" ] && exec starlark -cpuprofile "$PROFILE" "$@"

When it happens

Trigger: Running `starlark -cpuprofile` with no filename; a wrapper script that appends -cpuprofile conditionally but drops the path; typo where the path starts with '-' and is mistaken for another flag consuming it.

Common situations: Profiling scripts where the profile path variable is empty; flag ordering mistakes after copying documentation examples.

Related errors

• -c <cmd> flag needs an argument
• unknown flag: %s
• too many positional arguments
• Usage: %s -- command arg1 @args
• \nUsage: %s -- command arg1 @args\n

AI-assisted analysis of bazelbuild/bazel@e6e199d060 (2026-08-14). Data as JSON: /api/errors/6a832053b5394fba. Report an issue: GitHub.