Regarding rli2.exe
It seems that rli2.exe only compares the 'bigger' file against the smaller one. Meaning that we can't find unique lines in a rather small file comparing to an existing very big file.

A rather ugly solution would be to :
1.merge both files to one file
2.sort the merged file unique
3.sort the original big file merged file against the big file using rli2.exe

My question : Is there a more elegant option to get the unique difference  from a file.

Tried awk, but was short in memory (strerror).

Thank you for helping out here

dude, just flip the arguments around...
Thank you for replying even silly questions .... shame on me .... thanks to you!