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 occurences of each line along with that line:
sort <file> | uniq -c

# Display number of occurences of each line, sorted by the most frequent:
sort <file> | uniq -c | sort -nr