bash

name	bash
description	Write and fix Bash scripts with correct quoting, error handling, and ShellCheck compliance. Use when writing shell scripts, fixing shell quoting bugs, automating CLI tasks with Bash, or adding set -euo pipefail safety. Do not use for Python/Go CLI apps (prefer cli-development-python or cli-development-go) or for systemd unit files (prefer systemd-services).
license	Apache-2.0
compatibility	{"clients":["openai-codex","gemini-cli","opencode","github-copilot"]}
metadata	{"owner":"codex","domain":"bash","maturity":"draft","risk":"low","tags":["bash","shell","scripting"]}

Purpose

Write portable, safe Bash scripts with proper quoting, error handling, and ShellCheck compliance.

When to use this skill

• writing or editing .sh / .bash scripts
• automating file operations, build steps, or deploy tasks in shell
• debugging quoting errors, glob expansion, or word-splitting bugs
• adding safety headers (set -euo pipefail) to existing scripts

Do not use this skill when

• building a Go CLI binary — prefer cli-development-go
• building a Python CLI tool — prefer cli-development-python
• writing systemd unit files — prefer systemd-services
• the script is a cross-platform .sh/.ps1 pair — prefer cross-platform-shell

Procedure

1. Add safety header — start every script with #!/usr/bin/env bash and set -euo pipefail.
2. Quote all expansions — wrap every $variable in double quotes: "$var", "${arr[@]}". Use shellcheck to catch misses.
3. Use [[ ]] over [ ] — double brackets prevent word-splitting and support regex. Never use unquoted test.
4. Prefer printf over echo — echo behavior varies across platforms. Use printf '%s\n' "$msg".
5. Handle errors explicitly — use trap cleanup EXIT for temp file removal. Check command exit codes with if ! cmd; then.
6. Use local variables in functions — declare with local to avoid polluting the global scope.
7. Validate inputs — check $# for argument count, validate file existence with [[ -f "$path" ]], reject empty strings.
8. Run ShellCheck — execute shellcheck -o all script.sh and fix every warning before committing.

Key patterns

#!/usr/bin/env bash
set -euo pipefail

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

cleanup() { rm -f "${tmp_file:-}"; }
trap cleanup EXIT

main() {
  local input="${1:?Usage: $0 <input-file>}"
  [[ -f "$input" ]] || { printf 'File not found: %s\n' "$input" >&2; return 1; }
  local tmp_file
  tmp_file="$(mktemp)"
  # process...
}

main "$@"

Array iteration:

files=("$SCRIPT_DIR"/*.txt)
for f in "${files[@]}"; do
  [[ -e "$f" ]] || continue
  process_file "$f"
done

Decision rules

• Never use eval or unquoted $() in conditionals.
• Redirect stderr for user-facing messages: echo "error" >&2.
• Use readonly for constants, local for function-scoped variables.
• Prefer command -v over which for portability.
• If a script exceeds 200 lines, consider rewriting in Python or Go.

References

• https://www.shellcheck.net/
• https://mywiki.wooledge.org/BashPitfalls
• https://google.github.io/styleguide/shellguide.html

Related skills

• cross-platform-shell — multi-OS shell scripts
• cli-development-python — complex CLI tools
• terminal-debugging — debugging shell execution
• linux-ubuntu-ops — system administration tasks