shell-style-guidelisted

# Shell Style Guide Review and write shell scripts following the [Google Shell Style Guide](https://google.github.io/styleguide/shellguide.html). ## When Writing Shell Scripts ### Use Bash Only - Use `#!/bin/bash` with minimal flags - Set shell options via `set` rather than shebang flags (e.g., `set -o errexit`, `set -o nounset`) - Caution: `(( ))` evaluating to zero returns non-zero, which causes exit under `set -e` - If a script exceeds ~100 lines or has complex control flow, recommend rewriting in Python or Go ### File Conventions - Executables: no extension (strongly preferred) or `.sh` - Libraries (sourced only): `.sh` extension, not executable - SUID/SGID: forbidden — use `sudo` instead ### Error Output Direct all error messages to STDERR: ```bash err() { echo "[$(date +'%Y-%m-%dT%H:%M:%S%z')]: $*" >&2 } ``` ## Review Checklist When reviewing shell code, check these categories in order: 1. **Critical bugs** — unquoted variables, missing error handling, unsafe `eval` 2. **Formatting** — 2-space indent, 80-char line limit, pipeline style 3. **Naming** — lowercase_with_underscores for functions/variables, UPPER_CASE for constants 4. **Best practices** — `[[ ]]` over `[ ]`, `$(cmd)` over backticks, arrays over space-delimited strings 5. **Structure** — `main` function pattern, functions grouped at top, comments on non-obvious logic For detailed rules and examples in each category, see [references/style-rules.md](references/style-rules.md). ## Key Rules Summa