plan9-uniq(1) - report repeated lines in a file
-u     Print unique lines.
-d     Print (one copy of) duplicated lines.
-c     Prefix a repetition count and a tab to each output line.  Implies -u and -d.
-num   The  first  num  fields together with any blanks before each are ignored.  A field is defined as a
       string of non-space, non-tab characters separated by tabs and spaces from its neighbors.