Shell scripting best practices and conventions for bash, sh, zsh, and other shells

# Shell Scripting Guidelines

Instructions for writing clean, safe, and maintainable shell scripts for bash, sh, zsh, and other shells.

## General Principles

- Generate code that is clean, simple, and concise
- Ensure scripts are easily readable and understandable
- Add comments where helpful for understanding how the script works
- Generate concise and simple echo outputs to provide execution status
- Avoid unnecessary echo output and excessive logging
- Use shellcheck for static analysis when available
- Assume scripts are for automation and testing rather than production systems unless specified otherwise
- Prefer safe expansions: double-quote variable references (`"$var"`), use `${var}` for clarity, and avoid `eval`
- Use modern Bash features (`[[ ]]`, `local`, arrays) when portability requirements allow; fall back to POSIX constructs only when needed
- Choose reliable parsers for structured data instead of ad-hoc text processing

## Error Handling & Safety

- Always enable `set -euo pipefail` to fail fast on errors, catch unset variables, and surface pipeline failures
- Validate all required parameters before execution
- Provide clear error messages with context
- Use `trap` to clean up temporary resources or handle unexpected exits when the script terminates
- Declare immutable values with `readonly` (or `declare -r`) to prevent accidental reassignment
- Use `mktemp` to create temporary files or directories safely and ensure they are removed in your cleanup handler