Claude cli unattended wrapper

Claude CLI Unattended Wrapper

When to use

You are running claude -p "<slash command>" from inside another process (daemon, pipeline, scheduled loop) and cannot have any interactive prompt — selection menu, "Proceed? [y/N]", permission ask — deadlock the child.

Shape (five concerns, each addressed separately)

Concern	Fix
Prompt too long for argv	Write prompt to a tempfile; cat it into claude -p's stdin
Interactive "y/N" mid-run	Append a file of y\n × 10 to the same pipe; any blocking read gets answered
Slash-command own selection UI	Use its native --yes / non-interactive flag first; stdin is the safety net
Permission prompt on tool use	--dangerously-skip-permissions (the parent must accept the blast radius)
Parent hooks hijacking I/O	Env vars that tell the wrapping harness to stay out of this child's I/O

Reference invocation (Node, cross-platform)

const tmp    = path.join(os.tmpdir(), `prompt-${Date.now()}.txt`);
const yesTmp = path.join(os.tmpdir(), `yes-${Date.now()}.txt`);
fs.writeFileSync(tmp, promptText, 'utf8');
fs.writeFileSync(yesTmp, 'y\n'.repeat(10), 'utf8');

// `cat` exists on both git-bash/WSL on Windows and on *nix. Avoid `type` because
// it mangles line endings and doesn't concat two files in a single stream.
const cmd =
  `cat "${tmp}" "${yesTmp}" | claude -p ` +
  `--dangerously-skip-permissions --output-format stream-json --verbose`;

const child = spawn(cmd, [], {
  shell: true,
  stdio: ['ignore', 'pipe', 'pipe'],
  env: { ...process.env, DISABLE_OMC: '1', OMC_SKIP_HOOKS: '*', CLAUDE_DISABLE_SESSION_HOOKS: '1' },
});

Rules

• Prompt via stdin, not argv. Argv length limits (≈32KB on Windows, ≈128KB on Linux) will bite once prompts include embedded URLs or context. Tempfile + pipe sidesteps it entirely and also dodges shell quote-escaping bugs.
• Concatenate the auto-yes file onto the same pipe. Two separate echo y commands won't reach a child that only reads stdin once; a single cat promptFile yesFile | gives one continuous stream.
• Always set a timeout. A stuck child can silently hold the pipeline forever. 30 min is a reasonable outer bound for a single slash command; anything longer is a bug. setTimeout(() => child.kill(), timeoutMs) then clean up on close.
• Clean the tempfiles in the close handler. Both the happy path and the error path must unlinkSync the two tempfiles — otherwise /tmp fills up in loops that run thousands of times a day.
• Use --output-format stream-json --verbose. That way the parent can parse each assistant message, tool_use, and result event line-by-line instead of waiting for the whole transcript. Pair it with a stream-json consumer (see linked skill).
• Phrase the prompt to pre-answer everything. Even with the stdin safety net, the prompt itself should spell out: "answer 'y' to any interactive prompt", "if asked to select, choose 'all'", "do not ask me any follow-up questions". Belt and suspenders.

Counter / Caveats

• --dangerously-skip-permissions is exactly what the name says. The child can run arbitrary git clone, rm, curl, etc. Accept this only if the parent has already fenced the child: scoped working dir, no production credentials in env, outbound network confined.
• On Windows, cat is only present if git-bash or WSL is installed. PowerShell's cat is an alias for Get-Content which prints with CRLF and differs in concat behavior — don't use it. If you must run from pure cmd.exe, shell out via bash -c "...".
• The y\n stream answers anything that reads from stdin, which means you also auto-confirm destructive prompts you didn't anticipate. Audit the slash commands you run for any "really delete? [y/N]" paths before enabling this in production.
• Hook-bypass env vars are specific to the OMC harness. If the parent is plain shell, they're no-ops — but costless. See linked knowledge entry.

Related

• Knowledge: claude-cli-hook-bypass-envs — why those three env vars matter and what each turns off.
• Knowledge: dangerously-skip-permissions-for-unattended-loops — risk accounting for the permission bypass.
• Skill: stream-json-assistant-event-router — how to consume the child's --output-format stream-json output.