This manual page
documents the GNU version of
uniq .
uniq
prints the unique lines in a sorted file, discarding all but one of a
run of matching lines. It can optionally show only lines that appear
exactly once, or lines that appear more than once.
uniq
requires sorted input because it compares only consecutive lines.
If the output file is not specified,
uniq
writes to the standard output. If the input file is not specified, it
reads from the standard input.