If the output is similar to the below one then diff tool is not installed in your system
diff: Try `diff --help' for more information.
3. Type the following command in the terminal
diff filename1 filename2
The above command will print the difference between the two files on the screen.
You can also direct the output to another file using following command.
diff filename1 filename2 >> filename3
You can also ignore case of file contents using follwoing command
diff -i --ignore-case filename1 filename2 >>filename3
4. For more options of diff
Type(in terminal) :