Question

I’ve got a busybox system which doesn’t have uniq and I’d like to generate a unique list of duplicated lines.

A plain uniq emulated in awk would be:

sort <filename> | awk '!($0 in a){a[$0]; print}'

How can I use awk (or sed for that matter, not perl) to accomplish:

sort <filename> | uniq -d

Answer 1

Could do this (needn’t sort it):

awk '{++a[$0]; if(a[$0] == 2) print}'