# Your first block

`git stash` is where an agent's uncommitted work goes to die: it stashes, forgets, and your changes are three `pop`s deep by the time you notice. Declare it off-limits -- the hook below is the complete file. Drop it in `.claude/hooks/`, and every Bash call the agent makes passes through it before running.

Type at it. Try `git stash`, then get sneaky -- hide it behind `cd`, chain it after `&&`, pipe into it. The code is editable, too: change the pattern and the verdicts follow.


Two things worth noticing:

**The family is covered.** `cd /tmp && git stash`, `true | git stash`, `git stash pop` -- one declaration catches the command anywhere in the line, not just at position zero.

**The quoted mention blocks too.** `echo "git stash"` is harmless, and it still blocks. That's deliberate: [block_command](../../reference/primitives.md#captain_hook.block_command) compiles to a conservative match that stops an innocent echo rather than miss a real stash smuggled through quoting. For a safety hook, false positives are cheap and false negatives are not.

Cheap for a guardrail -- expensive if you need the command to run. [Next: buy back precision with `Runs`.](../../docs/tutorial/command-vs-runs.md)