# Proof Grammar Bash Builtin

> A proof grammar fixture in which an off-allowlist Bash builtin sits between an allowlisted command and an exit report. The earlier candidate must not borrow the builtin's status. Never distributed. Trigger phrases - "Bash builtin proof boundary", "builtin borrowed report test".

- Skill: `island-dev-crew/proof-grammar-bash-builtin` (Agent Skill)
- Install (CLI): `npx skillmds@latest add island-dev-crew/proof-grammar-bash-builtin`
- Raw SKILL.md: https://api.skillmd.com/api/skills/island-dev-crew/proof-grammar-bash-builtin/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Docs & Writing
- Author: Island-Dev-Crew (https://skillmd.com/u/island-dev-crew)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/island-dev-crew/proof-grammar-bash-builtin

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# Bash builtin command boundary

The report belongs to Bash's `help` builtin, not to the Python candidate above it. Every Bash
builtin and keyword is a command boundary even when it is outside the verifier's run allowlist.

- `enforced`: `verify-proofs.py --strict` returns 4 with Python pending and `help` skipped.
- `advisory`: nothing else here is real.

```bash
python3 -c "import sys; sys.exit(0)"
help printf
echo $? # -> 0
```