uniq - report or omit repeated lines
Discard all but one of successive identical lines from INPUT (or standard input), writing to OUTPUT (or standard output).

Mandatory arguments to long options are mandatory for short options too.

-c, --count
prefix lines by the number of occurrences
-d, --repeated
only print duplicate lines
-D, --all-repeated[=delimit-method] print all duplicate lines
delimit-method={none(default),prepend,separate} Delimiting is done with blank lines.
-f, --skip-fields=N
avoid comparing the first N fields
-i, --ignore-case
ignore differences in case when comparing
-s, --skip-chars=N
avoid comparing the first N characters
-u, --unique
only print unique lines
-w, --check-chars=N
compare no more than N characters in lines
display this help and exit
output version information and exit
A field is a run of whitespace, then non-whitespace characters. Fields are skipped before chars.