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Re: [PATCH] Re: dd blocks/bytes at a time

From: Jim Meyering
Subject: Re: [PATCH] Re: dd blocks/bytes at a time
Date: Thu, 21 Dec 2006 20:15:15 +0100

Paul Eggert <address@hidden> wrote:
> Jim Meyering <address@hidden> writes:
>> Andreas Schwab <address@hidden> wrote:
>>> But only the preceding ones.
>> True.  Thanks.
> Wait a minute -- POSIX says bs= should override all ibs= and obs=
> operands (not just preceding ones), and traditional dd conforms to
> POSIX here.  So the GNU documentation was right and the behavior
> wrong.
> Here's a patch.
> 2006-12-21  Paul Eggert  <address@hidden>
>       * NEWS: dd bs= operands now silently override later ibs= and obs=,
>       as POSIX requires.
>       * src/dd.c (scanargs): Implement it.
>       * tests/dd/misc (outbytes): Test it.
>       * doc/coreutils.texi (dd invocation): Specify that bs=N
>       overrides later ibs and obs, undoing part of the
>       previous change.  (The behavior was wrong.)

Whoa.  Good catch.
I see that both freebsd6 and netbsd1.6 disallow the usage in
your test case:

  netbsd$ echo x | /bin/dd bs=3 ibs=10 obs=10 conv=sync | wc -c
  dd: ibs: illegal argument combination or already set

Solaris 10 does what you propose.
Can anyone check other implementations?

I'm beginning to think GNU dd should at least warn about
the portability problem.

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