Comparing two files and looking for possible differences on a Linux like operating system is a common action.
diff is one of those utilities that you get to know when you deal with text files.
It is part of the coreutils, bundle of utilities provided by GNU : Coreutils manual
If you simply want to know if two files are the same, the GNU version of diff comes up with this feature using the -s or –report-identical-files options.
More information : Debian manpage for diff