You can compare the difference of files in two folders in the Command Line by using the diff command.

With folders you use rq as an argument and pass in the 2 folder names on the command line like so…

diff  -rq folder_1 folder_2

You will get notifications on what same corresponding  files are different, as well as notifications of what  files are unique in each folder. Once you know what files are different you then can run the diff file command on those to see the actual difference.

With files you can pass these in to the Terminal/command line  with diff like so…

diff file_1 file_2

For files you can also use the great online tool Diff Checker.