auniq: filter out multiple lines - only one instance of an
input line will be printed.

By default the program assumes that the input lines are sorted (therefore
only successive lines will be printed in one line).

Parameters:
-c: count and print the number of occurences of the line
  (out xmpl: "2:apple")
-u: print only uniq lines (that occur only one time on the input)
-us: assumes unsorted input. Note that this mode can consume much more
memory than the sorted mode (the uniq lines must be stored in memory
until the end of the input). This mode prints the uniq lines
automatically in sorted order.