ref: c3ba64f6935322f09b6de5c2285544fd471c605d dir: /sys/lib/man/permind/dup2.awk/
$NF!=lastf2 {if(last2!="") print last2 lastf2=lastf1; last2=last1; lastf1=$NF; last1=$0} $NF==lastf2 {print} END {print last2; print last1}