Fedora :: Cannot Compare Two Directories And Print Files

I have to write a script that accepts two directory names (JIIT, JUIT) as positional parameters and checks which files are identical in both directories and files having same contents are also considered as identical in same directory. I tried using diff:

#both directories contain three files...file1, file2, file3
echo "Enter the directories:"
read d1
read d2
cd $d1

if diff file1.sh file2.sh > /dev/null
then echo same 1,2
else echo different
fi

if diff file1.sh file3.sh > /dev/null
then echo same 1,3
else echo different
fi

if diff file2.sh file3.sh > /dev/null
then echo same 3,2
else echo different
fi

cd ../
cd $d2
.....

I used the same code in the other directory for the three files. This is not running. I also want to know what to do when I need to compare files from different directories. i.e., JIIT, JUIT..