# show all lines without duplication
# `sort -u` and `uniq` is the same effect.
sort file | uniq

# show not duplicated lines
sort file | uniq -u

# show duplicated lines only
sort file | uniq -d

# count all lines
sort file | uniq -c

# count not duplicated lines
sort file | uniq -uc

# count only duplicated lines
sort file | uniq -dc