me:/tmp$ dd if=/dev/urandom of=testinput.dat count=3
3+0 records in
3+0 records out
1536 bytes (1.5 kB, 1.5 KiB) copied, 0.000223026 s, 6.9 MB/s
me:/tmp$ dd if=/dev/urandom of=testoutput.dat count=3
3+0 records in
3+0 records out
1536 bytes (1.5 kB, 1.5 KiB) copied, 7.5333e-05 s, 20.4 MB/s
me:/tmp$ nano compare.sh
me:/tmp$ sh compare.sh
       0: testinput.dat testoutput.dat differ: byte 1, line 1 is  77 ? 246 M-&
     400: testinput.dat testoutput.dat differ: byte 1, line 1 is  36 ^^ 231 M-^Y
me:/tmp$ sh -x compare.sh
+ f1=testinput.dat
+ f2=testoutput.dat
+ stat -c%s testinput.dat
+ size=1536
+ i=0
+ [ 0 -lt 1536 ]
+ cmp -n 1024 -i 0 -b testinput.dat testoutput.dat
+ r=testinput.dat testoutput.dat differ: byte 1, line 1 is  77 ? 246 M-&
+ printf %8x: %s\n 0 testinput.dat testoutput.dat differ: byte 1, line 1 is  77 ? 246 M-&
       0: testinput.dat testoutput.dat differ: byte 1, line 1 is  77 ? 246 M-&
+ expr 0 + 1024
+ i=1024
+ [ 1024 -lt 1536 ]
+ cmp -n 1024 -i 1024 -b testinput.dat testoutput.dat
+ r=testinput.dat testoutput.dat differ: byte 1, line 1 is  36 ^^ 231 M-^Y
+ printf %8x: %s\n 1024 testinput.dat testoutput.dat differ: byte 1, line 1 is  36 ^^ 231 M-^Y
     400: testinput.dat testoutput.dat differ: byte 1, line 1 is  36 ^^ 231 M-^Y
+ expr 1024 + 1024
+ i=2048
+ [ 2048 -lt 1536 ]
me:/tmp$
me:/tmp$
me:/tmp$ # following direct paste:
me:/tmp$
me:/tmp$
me:/tmp$ #!/bin/sh
me:/tmp$
me:/tmp$ f1=testinput.dat
me:/tmp$ f2=testoutput.dat
me:/tmp$
me:/tmp$ size=$(stat -c%s $f1)
me:/tmp$ i=0
me:/tmp$ while [ $i -lt $size ]; do
>   if ! r="`cmp -n 1024 -i $i -b $f1 $f2`"; then
>     printf "%8x: %s\n" $i "$r"
>   fi
>   i=$(expr $i + 1024)
> done
       0: testinput.dat testoutput.dat differ: byte 1, line 1 is  77 ? 246 M-&
     400: testinput.dat testoutput.dat differ: byte 1, line 1 is  36 ^^ 231 M-^Y
me:/tmp$