Destructive Bash PreToolUse Hook (Claude Code)

Blocks rm -rf, DROP TABLE, git push --force / -f, TRUNCATE, and DELETE FROM without WHERE before Claude Code runs them.

Logs every block to ~/.claude/hooks/blocked.log with timestamp, command, and project path.

Install (2 commands)

mkdir -p ~/.claude/hooks && cp block_destructive.py ~/.claude/hooks/ && chmod +x ~/.claude/hooks/block_destructive.py

python3 - <<'PY'
import json, pathlib
p = pathlib.Path.home()/".claude"/"settings.json"
cfg = json.loads(p.read_text()) if p.exists() else {}
hooks = cfg.setdefault("hooks", {})
pre = hooks.setdefault("PreToolUse", [])
entry = {
  "matcher": "Bash",
  "hooks": [{
    "type": "command",
    "command": "python3 ~/.claude/hooks/block_destructive.py",
    "timeout": 5
  }]
}
# idempotent: skip if already wired
if not any(
  h.get("matcher")=="Bash" and any(
    "block_destructive.py" in (x.get("command") or "")
    for x in h.get("hooks", [])
  ) for h in pre
):
  pre.append(entry)
  p.write_text(json.dumps(cfg, indent=2) + "\n")
  print("hooks registered in", p)
else:
  print("already registered")
PY

Restart Claude Code (or start a new session).

What is blocked

Pattern	Example blocked	Allowed
rm -rf	rm -rf /tmp/x	rm file.txt
DROP TABLE	DROP TABLE users;	—
git push --force	git push -f origin main	git push origin main
TRUNCATE	TRUNCATE TABLE logs	—
DELETE FROM no WHERE	DELETE FROM users;	DELETE FROM users WHERE id=1

Manual test

echo '{"tool_name":"Bash","tool_input":{"command":"rm -rf /tmp/demo"},"cwd":"/tmp"}' \
  | python3 block_destructive.py ; echo exit:$?
# expect exit 2 + deny JSON

echo '{"tool_name":"Bash","tool_input":{"command":"ls -la"},"cwd":"/tmp"}' \
  | python3 block_destructive.py ; echo exit:$?
# expect exit 0

tail -n 3 ~/.claude/hooks/blocked.log

Acceptance checklist

• Claude Code hooks format (~/.claude/hooks/ + settings PreToolUse)
• Blocks required destructive patterns
• Logs timestamp, command, project path
• Clear message to Claude (systemMessage + exit 2)
• Does not interfere with normal bash
• README install in ≤2 commands

Author

@cornerblue — BTC: bc1qjtevjy8gldfhkra6n5g4yclpr5uafyd7k0j2ls