GNU bug report logs - #69532
mv's new -x option should be made orthogonal to -t/-T/default

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From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Paul Eggert <eggert <at> cs.ucla.edu>, Pádraig Brady <P <at> draigBrady.com>
Cc: 69532 <at> debbugs.gnu.org, util-linux <util-linux <at> vger.kernel.org>, Dominique Martinet <asmadeus <at> codewreck.org>, Petr Malat <oss <at> malat.biz>, Karel Zak <kzak <at> redhat.com>, Rob Landley <rob <at> landley.net>
Subject: bug#69532: mv's new -x option should be made orthogonal to -t/-T/default
Date: Wed, 20 Mar 2024 20:43:40 +0100

On 3/17/24 07:10, Paul Eggert wrote:
> Although removing that "mv --swap" implementation was a win, I don't
> think we can simply delegate this to util-linux's exch command.

I still have some headache adding this.

This stems from the fact that although mv(1) is a userland frontend
for renameat(2), the user interface is different:
while renameat(2) deals exactly with 2 operands, mv(1) has always
been able to work on more arguments.

Now, extending "exchange" to more arguments is confusing and the
use is not intuitive:
  mv -v --exchange  a b c d

An "exchange" can literally only be applied to 2 files,
and 'exch' is IMO fine.

I have the gut feeling that we didn't think through all cases,
and that some might be surprising, e.g.:

  $ mkdir d; echo 1 > a; echo 2 > d/a
  $ src/mv --exchange a a a a d/a

versus

  $ src/mv --exchange a a a a d/a

Have a nice day,
Berny

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