comparing tar output to directory list files

We have a script that executes the line below:

find . -name '*' -print > datalisttmp.txt

this creates a directory listing of a selected folder in a text file. We then remove the './' from the beginning of each line with the following:

cut -c 3- datalisttmp > datalist2.txt

this creates the same directory listing but with out the leading './'. We then have a tar command that backs up the selected directory and pipes the verbos data to a file:

tar czvf /backup.tar /selectedfile > /datalisttar.txt

How do you compare the 'datalist2.txt' file to the 'datalisttar.txt' file to find out what is different, ie: not found in the tar?

diff? cmp?

I don't think that cmp is the right answer in this case. We are trying to compare two text files to find out what files were not backed up in the tar file.

Okay, but diff should work fine.