developing-posix-shell-scripts skill
This skill covers any task involving writing, reviewing, or refactoring a POSIX-compliant shell script (/bin/sh).
Bash-specific features are forbidden. See common.md for the full list of bash-isms to avoid.
Step 1 — Classify the Script
Audit flags before classifying. Ask for each proposed flag: would a real caller ever pass a different value, or can it be a readonly constant? Beyond that, apply common sense — not everything that *could* vary *should* be a flag. Internal paths, fixed timeouts, log levels for non-CLI tools, and similar values are typically hardcoded in practice even if they could theoretically differ. When reviewing an existing script, re-classify from scratch; the current number of flags is not evidence of correct classification.
Simple — all of: < 50 lines of logic, 0–2 genuine flags, no structured logging, no -h/help output, no resource cleanup, not shared across systems/environments.
Complex — any of: ≥ 50 lines, 3+ genuine flags, structured logging, -h/help output, resource cleanup, shared across systems/environments.
When in doubt, prefer Simple.
Step 2 — Follow the Reference Document
Always load common.md first, then load the matching document:
- developing-simple-posix-shell-scripts.md — Load when classified as Simple.
- developing-complex-posix-shell-scripts.md — Load when classified as Complex. Also load reference-code-blocks.md to compose only the blocks the script actually needs.