When you copy a directory with many files, you may want to check whether the copied directory is indeed an exact copy of the original. You can do that by comparing all files. You can write your own script checking every single file. You can also use standard tools under linux such as the diff command:
diff -r folder folder2 | grep -v "^diff -r " | sort
Here, the diff command check for all files recursively (-r). It returns a so-called diff file format including the differences. If we are interested by which files are different only, then we can use the grep command to simply return the file names that differ.