Write a Shell Program That Overwrite File

case $# in
0 | 1) echo "Usage : overwriteFile.sh file cmd [arguments]" ;;
esac

file=$1;shift
new=/tmp/overwrte.$$; old=/tmp/overwrte.$$;
trap 'rm -f $new $old;exit 1;' 1 2 15

if PATH=$opath "$@" > $new
then
    cp $file $old
    trap '' 1 2 15
    cp $new $file
else
    echo "overwrite failed !"
    exit 1
fi

rm -f $new $old