sort, merge, or sequence check text files

-r     Reverse the sense of comparisons.

The treatment of field separators can be altered using the options:

-n     Restrict the sort key to an initial numeric string,  consisting  of  optional  <blank>s,  optional
       minus  sign, and zero or more digits with an optional radix character and thousands separators (as
       defined in the current locale), which shall be sorted by arithmetic value. An empty  digit  string
       shall be treated as zero.  Leading zeros and signs on zeros shall not affect ordering.