denoland/deno · info · ERR_MISSING_ARGS

ERR_MISSING_ARGS

ERR_MISSING_ARGS

Error message

The "file" argument must be specified

What it means

The REPL dot-command `.save` writes every line evaluated in the current session to a file. It requires a filename argument; when invoked with none (`file === ''`) it throws ERR_MISSING_ARGS, which the command's own catch block converts into the printed line 'The "file" argument must be specified' before re-displaying the prompt. The error never escapes to the session.

Source

Thrown at ext/node/polyfills/repl.ts:474

          longestNameLength - name.length + 3,
        );
        const line = `.${name}${cmd.help ? spaces + cmd.help : ""}\n`;
        this.output.write(line);
      });
      this.output.write(
        "\nPress Ctrl+C to abort current expression, " +
          "Ctrl+D to exit the REPL\n",
      );
      this.displayPrompt();
    },
  });

  repl.defineCommand("save", {
    help: "Save all evaluated commands in this REPL session to a file",
    action: function (this: REPLServer, file: string) {
      try {
        if (file === "") {
          throw new ERR_MISSING_ARGS("file");
        }
        fs.writeFileSync(file, ArrayPrototypeJoin(this.lines, "\n"));
        this.output.write(`Session saved to: ${file}\n`);
      } catch (error) {
        if ((error as { code?: string })?.code === "ERR_MISSING_ARGS") {
          this.output.write(`${(error as Error).message}\n`);
        } else {
          this.output.write(`Failed to save: ${file}\n`);
        }
      }
      this.displayPrompt();
    },
  });

  repl.defineCommand("load", {
    help: "Load JS from a file into the REPL session",
    action: function (this: REPLServer, file: string) {
      try {

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Type the command with a path: `.save /tmp/session.js`
2. Check the syntax — the filename follows the command separated by a space, e.g. `.save session.log`

Example fix

// before
deno> .save
The "file" argument must be specified

// after
deno> .save session.js
Session saved to: session.js

// programmatic REPL driver: check the filename before sending .save
const file = process.argv[2];
if (!file) {
  console.error('usage: .save <file>');
} else {
  replServer.write(`.save ${file}\n`);
}

When it happens

Trigger: Typing `.save` with no filename (the REPL trims the rest of the line to an empty string) in a `deno` or node:repl session.

Common situations: Users expecting `.save` alone to pick a default file (like shell history tools); typos such as `.save>`; scripted/programmatic REPL input that forgets to append the path.

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

• failed to evaluate expression
• Unexpected third argument to Deno.bench()
• Invalid type for fetch: must be a function
• Invalid type for onListen: must be a function
• ERR_MISSING_ARGS

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/c47a6dc62ffdbb24. Report an issue: GitHub.