path-sensitive-shell-safety

Path-Sensitive Shell Safety

Use this skill before editing or reviewing shell, deploy, installer, cleanup, or repair logic that builds filesystem paths from variables or touches remote repositories.

Common triggers:

• Path variables such as remote_base, repo_dir, repo_folder, target_dir, backup_dir, worktree, site, app, or user-entered folder names.
• Destructive or path-sensitive commands: rm, mv, cp -a, rsync --delete, find -delete, docker volume rm, git clean, git reset, checkout repair, clone replacement, or symlink-sensitive copy.
• Git sync that decides which branch or remote checkout will be deployed.

Safety objective

No empty, unset, broad, symlinked, or unintended path may reach a destructive command. Validate values before joining paths, validate the joined path before use, and validate containment immediately before the command.

Required workflow

1. Identify the command with the highest blast radius.
2. List every variable that contributes to its path or repository target.
3. Classify each variable:
   • trusted constant;
   • config value;
   • remote/server value;
   • user/operator input;
   • derived path.
4. Validate raw inputs before joining:
   • required and non-empty;
   • expected shape: absolute base path or safe single folder segment;
   • no traversal, newlines, glob metacharacters, leading option dash, or control characters;
   • explicit allowlist for server roots when possible.
5. Join paths with quoted expansions only. Do not use eval.
6. Canonicalize existing paths with physical resolution (pwd -P or realpath) before destructive work.
7. Assert containment:
   • target is inside the approved base;
   • target is not /, ., .., $HOME, the base root itself, or another broad system directory;
   • target is not a symlink unless the operation explicitly supports symlinks.
8. Put the final guard directly next to the dangerous command.
9. Use command terminators and quoting: -- "$path" where supported.
10. For Git sync, verify expected origin, selected branch policy, fetch success, clean worktree, fast-forward state, and final HEAD == origin/<branch> before build/deploy.
11. Run the repo validation command and AgentShield probe when this changes agent surfaces or automation rules.