lines=$(grep '^[^:]+::' /etc /shadow)

if [ "$lines" == "" ]; then

var=$(exit 2)$(exit 4)

if lines=$(grep '^[^:]+::' /etc/shadow); then
  printf 'There are users with an empty password:n%sn' "$lines"
else
  printf 'OK, no user with empty passwords'
fi

grep '^[^:]+:.:' /etc/shadow