Bash mode lets you drop straight into the shell without spending a turn asking Claude to run a command.

What it does

Start any prompt with ! and the rest of the line runs as a shell command. Output appears inline and is captured into the conversation so Claude can reference it on the next turn. This is faster than please run ls -la and more honest - you're not spending tokens on the interpreter round-trip.

When to use it

Quick directory listings, git status checks, or file inspections.
Sanity-checking the shell state before asking Claude to do real work.
Piping output into a follow-up Claude prompt without editing files.
Teaching Claude about your environment without explaining it.

Gotchas

Bash mode respects your current permission rules. Denied commands still get blocked.
The working directory is the same as Claude's Bash tool, not wherever your outer terminal sits.
Shell state (exported vars, aliases) doesn't persist between bash-mode calls unless you use SessionStart hooks.

Official docs: https://code.claude.com/docs/en/interactive-mode.md#bash-mode-with--prefix