To find repeated matches by `uniq -d`

Question

My data as /tmp/1

9367543
9105616
9108177
8948074
8860323
9170406
9105616

I run and I get nothing

cat /tmp/1 | uniq -d

This is strange, since uniq -d should

-d      Only output lines that are repeated in the input.

How can you use uniq -d?

Answer 1

You have to sort your data before you use uniq. It only removes/detects duplicates on adjacent lines.

Answer 2

Try this to double check, it will output any lines which are duplicated:

  cat /tmp/1 |  awk 'seen[$0]++ == 1'

Oh, this is your problem:

 cat /tmp/1 | sort | uniq -d

Sort it before running uniq!

Answer 3

awk '{_[$0]++}END{for(i in _)if(_[i]>1) print i}' /tmp/1

or just

awk '_[$0]++ == 1' file