uniq

Output the unique lines from the given input or file. Since it does not detect repeated lines unless they are adjacent, we need to sort them first.

Display each line once:

sort {{file}} | uniq

Display only unique lines:

sort {{file}} | uniq -u

Display only duplicate lines:

sort {{file}} | uniq -d

Display number of occurrences of each line along with that line:

sort {{file}} | uniq -c

Display number of occurrences of each line, sorted by the most frequent:

sort {{file}} | uniq -c | sort -nr