From: Paul Eggert <eggert@cs.ucla.edu>
To: "Bernhard Voelker" <mail@bernhard-voelker.de>,
"Pádraig Brady" <P@draigBrady.com>
Cc: Petr Malat <oss@malat.biz>,
util-linux <util-linux@vger.kernel.org>,
Dominique Martinet <asmadeus@codewreck.org>,
69532@debbugs.gnu.org, Karel Zak <kzak@redhat.com>,
Rob Landley <rob@landley.net>
Subject: Re: bug#69532: mv's new -x option should be made orthogonal to -t/-T/default
Date: Wed, 20 Mar 2024 13:56:44 -0700 [thread overview]
Message-ID: <4356f3eb-544e-4ce9-b9ea-374cd01663d5@cs.ucla.edu> (raw)
In-Reply-To: <11c9a6a2-c73d-4b99-b071-48e7eab2fd19@bernhard-voelker.de>
On 3/20/24 12:43, Bernhard Voelker wrote:
> 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.
Yes, that's mv's original sin, which we cannot realistically change now.
> 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,
Sure, but that's true for "rename" too: a "rename" can be applied only
to 2 files.
When d is a directory, "mv a b c d" does three renames so it is like "mv
a d/a; mv b d/b; mv c d/c". This remains true if you uniformly replace
"mv" with "mv --exchange", which does three exchanges.
> 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
I don't understand the word "versus" here, as the two examples look the
same to me.
If d/a is not a directory, the example is an error, just as it would be
without --exchange.
If d/a is a directory and you have permissions etc., "mv a a a a d/a" is
like attempting "mv -T a d/a/a; mv -T a d/a/a; mv -T a d/a/a; mv -T a
d/a/a". If you use plain "mv" only the first "mv -T a d/a/a" succeeds
because "a" goes away, so you get three diagnostics for the remaining
three "a"s. If you use "mv --exchange" all four "mv --exchange -T a
d/a/a" attempts succeed, and since there are an even number of exchanges
the end result is a no-op except for updated directory timestamps. So I
don't see any ambiguity about what mv should do with this contrived example.
next prev parent reply other threads:[~2024-03-20 20:56 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <10c814a7-cb68-4fb4-ad8d-f88f286fb0b1@cs.ucla.edu>
[not found] ` <58281f96-f9c6-4567-e3c9-c6a6cfa6ce27@draigBrady.com>
[not found] ` <ZeZqzB4-OzHYfFeQ@codewreck.org>
[not found] ` <5914e8b2-48ac-456b-9753-6a7bae7a9bbb@cs.ucla.edu>
2024-03-05 14:16 ` bug#69532: mv's new -x option should be made orthogonal to -t/-T/default Pádraig Brady
2024-03-05 20:41 ` Karel Zak
2024-03-05 22:13 ` Masatake YAMATO
2024-03-17 6:10 ` Paul Eggert
2024-03-17 11:32 ` Pádraig Brady
2024-03-17 11:40 ` Pádraig Brady
2024-03-20 22:10 ` Paul Eggert
2024-03-20 19:43 ` Bernhard Voelker
2024-03-20 20:56 ` Paul Eggert [this message]
2024-03-20 22:53 ` Bernhard Voelker
2024-03-20 23:56 ` Paul Eggert
2024-03-21 21:45 ` Bernhard Voelker
2024-03-23 1:44 ` Paul Eggert
2024-03-23 10:24 ` Bernhard Voelker
2024-03-22 10:22 ` Karel Zak
2024-03-23 10:24 ` Bernhard Voelker
2024-03-21 0:03 ` Rob Landley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4356f3eb-544e-4ce9-b9ea-374cd01663d5@cs.ucla.edu \
--to=eggert@cs.ucla.edu \
--cc=69532@debbugs.gnu.org \
--cc=P@draigBrady.com \
--cc=asmadeus@codewreck.org \
--cc=kzak@redhat.com \
--cc=mail@bernhard-voelker.de \
--cc=oss@malat.biz \
--cc=rob@landley.net \
--cc=util-linux@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.