Plan 9 from Bell Labs’s /usr/web/sources/plan9/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}
