#! @BASH@

set -e
usage () { echo >&2 "$0 FILE ... -- PROG ARGS"; exit 1; }
case "$#:$1" in
  0:* | 1:-h | 1:--help)
    echo "$0 FILE ... -- PROG ARGS"
    echo "  For each FILE, run PROG ARGS with stdin from FILE.  If all is"
    echo "  good, replace each FILE with the corresponding output."
    echo "  Clobbers FILE.old and FILE.new."
    exit 0
    ;;
esac
declare -a file
while :; do
  [ $# -eq 0 ] && usage
  f=$1; shift
  [ "$f" = -- ] && break
  file=("${file[@]}" "$f")
done
[ $# -eq 0 ] && usage

cleanup_a () {
  for f in "${file[@]}"; do
    rm -f "$f.new" "$f.old"
  done
}
trap cleanup_a EXIT INT QUIT TERM

for f in "${file[@]}"; do "$@" <"$f" >"$f.new"; done
for f in "${file[@]}"; do cp "$f" "$f.old"; done

cleanup_b () {
  for f in "${file[@]}"; do
    rm -f "$f.new"
    mv "$f.old" "$f"
  done
}
trap cleanup_b EXIT INT QUIT TERM

for f in "${file[@]}"; do mv "$f.new" "$f"; done
trap '' EXIT INT QUIT TERM
for f in "${file[@]}"; do rm -f "$f.old"; done
exit 0