Shell (`run_shell_command`)

Executes a shell command. On macOS/Linux, runs with bash -c. On Windows, runs with cmd.exe /c.

Parameters

Parameter	Required	Description
`command`	Yes	The exact shell command to execute
`description`	No	Brief description shown to the user
`directory`	No	Directory to run in (relative to project root; default: project root)
`is_background`	Yes	`true` for long-running processes; `false` for one-time commands
`timeout`	No	Timeout in ms (max 600,000)

is_background is required — all shell commands must explicitly declare whether they are background processes.

Foreground vs background

Use is_background: false for:

Build commands (npm run build, make)
Install commands (npm install)
Git operations (git commit, git push)
Test runs (npm test)
One-time queries (ls, cat)

Use is_background: true for:

Development servers (npm run dev, python -m http.server)
Build watchers (webpack --watch)
Database servers (mongod, redis-server)
Any process that runs indefinitely
Long batch jobs whose stdout you want to inspect later (evals, data processing)

Output

For foreground commands, the tool returns Command, Directory, Stdout, Stderr, Error, Exit Code, Signal, and Process Group PGID.

For background commands on non-Windows, the tool returns:

Task ID — opaque stable ID used to refer to the task later
Output file — absolute path where stdout+stderr is captured (writes continue after the wrapper exits)
PID — actual subprocess PID

Read the output file at any time with the read_file tool to inspect progress or final results — there is no need to poll. When the process exits, the next user prompt is prefixed with a <task_notification> block carrying task_id, output_file, status (completed/failed/killed), exit_code, and a human summary.

Background tasks

Output files live at <projectTempDir>/<sessionId>/tasks/<taskId>.output and are written via shell-level redirection (( cmd ) > file 2>&1 &). The OS keeps writing even after the parent shell exits, so detached processes never silently lose output.

To stop a runaway background task, use the bg_stop tool with the task_id. It SIGTERMs the process group and escalates to SIGKILL after a 3-second grace.

To list running and recently-completed background tasks from the TUI, run /bg.

Windows. Background tasks rely on POSIX shell redirection and process-group signaling. On Windows, is_background: true falls back to the simpler “fire and return” path used in earlier versions; output is not captured to disk.

Confirmation

Requires confirmation by default. Auto-approved in auto-edit mode (shell commands still need approval) unless yolo mode.

Security

Shell commands run with your user permissions. Use Sandboxing to restrict what commands can do, and Hooks to enforce policies on specific commands.

Shell (run_shell_command)