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---
name: write-bash-scripts
description: >-
Apply Bash style conventions when creating, editing, or reviewing Bash
scripts. Not for zsh; use write-zsh-scripts.
---
# Bash Style Guide
Apply the Bash conventions from `./references/BASH.md` when creating or editing Bash scripts.
## Key Conventions
Read `./references/BASH.md` for the complete guide. Summary:
### Script Structure
- Shebang: `#!/usr/bin/env bash`
- Strict mode: `set -euo pipefail`
- Main function called at end: `main "$@"`
### Naming
- Functions: `snake_case`
- Local variables: `lower_case`
- Constants: `ALL_CAPS` with `readonly`
### Syntax
- Variable expansion: `${var}` not `$var`, except the argument lists `"$@"` and `"$*"`, which stay unbraced
- Command substitution: `$(...)` not backticks
- Tests: `[[...]]` not `[...]`
- Function syntax: `function name() { }` with both keyword and parentheses
### Quoting
- Always quote variable expansions: `"${var}"`
- Always quote command substitutions: `"$(cmd)"`
- Use arrays for lists, not word splitting
- Guard an array that can be empty: `${array[@]+"${array[@]}"}`
### Local Variables
- Declare with `local`
- Separate declaration from command substitution to preserve exit codes
### Bash 3.2 (macOS)
macOS ships bash 3.2 as `/bin/bash`, which is what `#!/usr/bin/env bash` finds on a stock Mac. Under `set -u` it exits on an empty `"${@}"` or `"${array[@]}"`, and it has no associative arrays, `readarray` or `mapfile`, `${var,,}` or `${var^^}`, or namerefs. See "Bash 3.2 (macOS)" in `./references/BASH.md` for replacements.
## Pull Request Review
When reviewing a pull request, apply `./references/review-checklist.md`: the rules of this guide that a reviewer can check in a diff, ranked as Important, Nits and Do not flag. The same checklist is installed into repositories for automated reviewers, so update it whenever a rule here changes.
## Validation
Whenever possible, validate the script before finishing. Prefer using a project-specific validation script, if available. Common locations include declarations in `package.json` and scripts stored in `bin/`. If those aren't present, `shellcheck` is a commonly available linter for Bash scripts.
