#!/bin/sh
[ -t 2 ] && { red=$(printf "\033[31m"); sgr0=$(printf "\033[0m"); }

error() {
  echo "${red}ERROR:${sgr0} ${1}" >&2;
  exit 1
}

[ -n "$1" ] || error "input file missing"
[ -r "$1" ] || error "can't read input file"

# shellcheck disable=SC2016 # I don't want $(tty) to be expanded
printf '#!/bin/sh
GPG_TTY=$(tty)
export GPG_TTY
base64 -d <<EOF | gpg -d
%s
EOF
'   "$(gpg -c --cipher-algo AES256 -o - -- "$1" | base64)"