Safe Bash script template

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

cleanup() {
  # Remove temporary files or stop background jobs here.
  :
}
trap cleanup EXIT

main() {
  local input="${1:?usage: $0 <input-file>}"
  [[ -f "$input" ]] || { echo "not a file: $input" >&2; exit 1; }
  echo "processing $input"
}

main "$@"