Compare two files and append the difference at the bottom : I would like to first compare two files (`POSCAR.init` and `POSCAR.final`) in the link https://www.dropbox.com/sh/w9z7psuzq3qo9jm/AAAhySzuiYv08LPWpfFTaxtoa?dl=0
and then append the differences at the end of the respective files. The final files should look like `test.init` and `test.final` where one can see I manually put the differences at the bottom. If one uses `sdiff test.init test.final` one can see the difference appears now in the last line (ignore the first line). Since I have many folders like `stack` in the link given above, I am looking for some loop where basically I go to every folder, pick the difference between two files and then append the difference at the end as I explained above. Please let me know if anyone has some idea, I would very much appreciate it. 

N.B: Please note that I already looked a bit related-type queries such as here (https://stackoverflow.com/questions/4544709/compare-two-files-line-by-line-and-generate-the-difference-in-another-file) but that still not exactly the solution I am looking for here.