#! /bin/sh

set -e
case "$#:$1" in
  0:* | 1:-h | 1:--help)
    echo "$0 FILE PROG ARGS"
    echo "  Run PROG with ARGS, writing its stdout to FILE if it succeeds."
    echo "  Clobbers FILE.new."
    exit 0
    ;;
  1:*)
    echo >&2 "$0 FILE PROG ARGS"
    exit 1
    ;;
esac
file=$1; shift
set +e; "$@" >"$file.new"; st=$?; set -e
if [ $st -eq 0 ]; then
  mv "$file.new" "$file"
else
  rm "$file.new"
fi
exit $st