This thread is titled "Processing of log files".

I don't want "Basically, the requirement is to process...". I gave you an explicit list of .log files in post #4 and asked what output you want when given that list of .log files.

Instead of answering that question you showed us an unsorted list of .log and .doc files (with some of those of files included in the list twice). Are .doc files now considered log files?

How did you get a list of files with duplicate names in that list? If you ran a find command to produce a combined list of files from multiple directories and stripped off the directory names, how do you expect a script to be able to guess at which directory a file came from to determine its size?

You have said you want to process the files with a suffix a.log and b.log and you imply that a file named ski2015.12.15.12.30.23.log doesn't have a suffix because there is no _ in that name. Please take the list I gave you or the list you gave us in post #5 and show us the EXACT output that you want to produce from that list (and explain why some files, if there are any, are not included in the output).

It is easy to see that a sort that sorts a list in reverse numeric order (when the field being sorted is not numeric) and for matching fields on that key sorts in increasing alphanumeric order on a second key doesn't give you a list in the order you have described. What is not easy is trying to guess what files are supposed to be excluded from your output and the order you do want for files that are not excluded if some of those files do not contain an _ character.

Why do you need a list of "log" files other than that produced by letting the shell expand *.log as a filename matching pattern in the directory where these files are located? Or, if you only want files with a suffix (as you have described it), why not just use *_*.log to get the list?