Bash Tool - Claude Code

The Bash tool runs shell commands. It's the most capable and most-permissioned tool in Claude Code, which is why every session has at least one rule about it.

What it does

Bash runs a command in a persistent shell whose working directory sticks within the project. Output comes back as combined stdout+stderr, truncated if huge. You can run it in the background for long processes, pipe, use heredocs, and chain commands. Permission rules gate which commands are allowed.

When to use it

• Running tests, builds, linters, and formatters.
• Git operations, file system changes, and installs.
• Anything that's faster as a one-liner than a tool sequence.
• Invoking project-specific CLIs.

Gotchas

• Interactive prompts hang the tool. Pass flags or pipe input instead of waiting for TTY.
• Shell state (exported vars, cd in subshells) doesn't persist beyond a single call unless you chain with &&.
• Newlines are blocked in command strings on some setups. Use quoted strings or here-docs for multi-line payloads.

Official docs: https://code.claude.com/docs/en/tools-reference.md#bash-tool-behavior