The uniq(1) utility reads the standard input comparing
adjacent lines, and writes a copy of each unique input line to the
standard output. The second and succeeding copies of identical
adjacent input lines are not written. Repeated lines in the input
will not be detected if they are not adjacent, so it might be
necessary to sort the files first.
The following options are available:
Precede each output line with the count of the number of times
the line occurred in the input, followed by a single space.
Do not output lines that are not repeated in the input.
Ignore the first fields in each input line when doing
comparisons. A field is a string of non-blank characters separated
from adjacent fields by blanks. Field numbers are one based; that
is, the first field is field one.
Ignore the first chars characters in each input line
when doing comparisons. If specified in conjunction with the
-f option, the first chars characters after the first
fields fields will be ignored. Character numbers are one
based; that is, the first character is character one.
Do not output lines that are repeated in the input.
If additional arguments are specified on the command line, the
first such argument is used as the name of an input file, and the
second is used as the name of an output file.