How to count duplicate the lines of a file by using Linux Shell Programming?

I'm new to linux and to shell programming. I have an assignment to create a shell script that shows all the folders, sub folders and files of the current directory. LS does this. But I must count how many duplicate lines each file has, and show the line that is repeated the most times in each file.

I really have no idea where to start. How can I read/compare lines within a file?

Thanks in advance!

 

Start with searching google also and checking out these results

http://www.linuxquestions.org/questions/linux-software-2/finding-duplicate-lines-in-a-file-617441/

http://unstableme.blogspot.com/2008/03/remove-duplicates-without-sorting-file.html

 

cat filename | sort | uniq -c

Good luck