ref: 94e4c04561f7b9c2a3e7ef498fbfe7ce5b20ed40
dir: /testdir/t.8.y/
{$1=$2; print}
# this should print nothing for an empty input line
# since it has only referred to $2, not created it,
# and thus only $1 exists (and it's null).
# is this right???