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Re: Comparing Binary Files

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>>>>> Janis Papanagnou <janis_papanagnou@hotmail.com> writes:
>>>>> On 03.10.2016 06:52, lawrencedo99@gmail.com wrote:

[...]

 >> diff -u <(xxd /dev/dvd) <(xxd disc.iso)

 >> to compare hex dumps of the files instead.

 >> This works great--for example, showing me that the only difference
 >> is a few extra sectors of zero padding at the end of the disc.

 > That does not seem to be a satisfying solution in the general case;
 > even simple byte offsets by a few additional bytes at the beginning
 > of one file will show the whole files differing.  In that case a
 > "binary files differ" message would be preferable.  For the case of
 > changed bytes or additional data at the end of one file it's okay.

	As would be $ cmp -l, I suppose.

 >> However, it seems to use a lot of memory, even when no differences
 >> are found...

 > Why?  You are creating just to more processes and the shell
 > establishes two pipes for the diff.  I would not expect "a lot"
 > memory demand for that.

	Two reasons I can readily think of:

	* xxd(1) can easily turn a 4.5 GB DVD+R image into a 20+ GB
	  hexdump;

	* upon seeing that the files are indeed "binary", diff(1) may
	  refrain from running a memory-costly LCS algorithm and resort
	  to "exit (1) on the first byte that differs; exit (0) if none"
	  behavior that costs virtually no memory at all.

-- 
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Comparing Binary Files lawrencedo99@gmail.com - 2016-10-02 21:52 -0700
  Re: Comparing Binary Files Janis Papanagnou <janis_papanagnou@hotmail.com> - 2016-10-03 07:25 +0200
    Re: Comparing Binary Files lawrencedo99@gmail.com - 2016-10-02 22:48 -0700
      Re: Comparing Binary Files Janis Papanagnou <janis_papanagnou@hotmail.com> - 2016-10-03 09:12 +0200
        Re: Comparing Binary Files lawrencedo99@gmail.com - 2016-10-05 00:18 -0700
    Re: Comparing Binary Files Ivan Shmakov <ivan@siamics.net> - 2016-10-04 18:02 +0000
      Re: Comparing Binary Files lawrencedo99@gmail.com - 2016-10-04 11:32 -0700
      Re: Comparing Binary Files Janis Papanagnou <janis_papanagnou@hotmail.com> - 2016-10-05 10:01 +0200
        Re: Comparing Binary Files Ivan Shmakov <ivan@siamics.net> - 2016-10-07 12:30 +0000
  Re: Comparing Binary Files Rakesh Sharma <sharma__r@hotmail.com> - 2016-10-04 03:03 -0700
  Re: Comparing Binary Files Michael Paoli <michael1cat@yahoo.com> - 2016-10-06 01:32 -0700
    Re: Comparing Binary Files lawrencedo99@gmail.com - 2016-10-06 14:42 -0700

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