if diff -u "$file1" "$file2"; then
  echo "$file1 and $file2 have identical contents"
else
  : # the differences between the files have been listed
fi

# this will print if they're identical or not
diff file1 file2 -s

I=`wc -c $i | cut -d' ' -f1`
J=`wc -c $j | cut -d' ' -f1`
if [ $I -eq $J ]
then
      echo $i $j >> $1.pares
fi