You might note that the suggestion in post #5 in this thread invokes awk (using only standard awk features) once and sort twice producing both of the requested sorted outputs. Unlike some of the scripts in this thread, it doesn't need multiple invocations of sort or tr per file processed. And, theawk script processes one file at a time keeping only unique lines from that file (rather than keeping unique lines in memory from all files being processed). When the files being processed contain tens of thousands of input lines and tens of thousands of lines from most of those files are unique, that can chew up a lot of system resources.

And, although most of us corrected the use of sort without the n flag when sorting numeric values, none of us said why we did that. (If you use sort without the n flag, the sort performed is an alphanumeric sort; not a numeric sort. So, for example the string 9 is alphanumerically greater than the string 100000 because the leading digit 9 in the first string is greater than the leading digit 1 in the second string. When the n flag is given to sort, it performs a numeric sort instead of an alphanumeric sort for the key fields to which the flag is attached.)