Check all lines of a file are unique

Awk solution:

awk 'a[$0]++{print "dupes"; exit(1)}' file && echo "no dupes"

[ "$(wc -l < input)" -eq "$(sort -u input | wc -l)" ] && echo all unique

Using sort/uniq:

sort input.txt | uniq

To check only for duplicate lines use the -d option for uniq. This will show only lines that are duplicate, if none it will show nothing:

sort input.txt | uniq -d