echo sudo_o >&2
time tac <(seq 1 1000000) | awk 'a[$1]++{print $0 > "/dev/null";next}{print $0 > "/dev/null"}' 
 
echo -e "\nkent" >&2
time awk '$1 in a{print a[$1]>"/dev/null"}{a[$1]=$0}END{for(x in a)print a[x]}' <(seq 1 1000000) > /dev/null
 
 
echo -e "\nscrutinizer" >&2
time awk 'NR==FNR{A[$1]=NR; next} A[$1]!=FNR{print>f; next}1' f=/dev/null <(seq 1 1000000) <(seq 1 1000000) > /dev/null