From: Daniel Shahaf <d.s@daniel.shahaf.name>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: "zsh-workers@zsh.org" <zsh-workers@zsh.org>,
Martin Tournoij <martin@arp242.net>
Subject: Re: Any way to allow clobbering empty files when noclobber is set?
Date: Sat, 6 Jun 2020 04:48:08 +0000 [thread overview]
Message-ID: <20200606044808.59509bdf@tarpaulin.shahaf.local2> (raw)
In-Reply-To: <CAH+w=7b9WP77s5cTBO+gszHS=WJDLXzjjQqvU-E1Jdwz_jRwQw@mail.gmail.com>
Bart Schaefer wrote on Fri, 05 Jun 2020 18:07 -0700:
> (Martin, if you are no longer interested in these side discussions, we
> can stop Cc'ing you.)
>
> On Thu, Jun 4, 2020 at 8:10 PM Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
> >
> > Bart Schaefer wrote on Wed, 03 Jun 2020 22:00 -0700:
> > > Fair enough, although (silly example) "false > empty" would remove the
> > > file?
> >
> > Depends on whether ./empty was created by the redirection or not.
>
> Hm. That means that the following must all be preserved (in the
> parent shell, so fails for "exec command > file") all the way from the
> redirection event to the completion of the command:
> - whether the descriptor resulted from redirection
> - what kind of redirection operator was used
> - whether the appropriate clobber-related option was set at the time
> - how to identify the file we opened, in case something else renamed
> or removed it, and created another one of the same name in the
> meantime
>
> That seems at least impractical, especially the last one.
It'll just be a couple of local variables on the C stack, won't it?
For the last bullet, I suppose we could save the inode number (and
device number), but as I wrote in workers/45977, I don't see a way to
avoid a race condition.
> And what happens in the case of rename?
If the file has been renamed before we get around to unlink it, then we
won't unlink it. We won't have a choice.
> > Besides, if the redirection failed — I assume you mean the open(2)
> > failed — then isn't the unlink likely to fail as well?
>
> Open could fail because of file permissions. Unlink depends only on
> directory permissions.
>
Well, yes, but usually, if you don't have permission to read a file,
in practice you won't have permission to delete it either.
> > Okay. Is there a case where leaving around an empty file is worse than
> > removing it?
>
> IMO your examples are all too specific to warrant a generalized change
> in behavior of redirections.
Fair enough. As I said, just brainstorming.
Cheers,
Daniel
next prev parent reply other threads:[~2020-06-06 4:48 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200603020919eucas1p13e26ebcbb335784d14bfb97b137f385a@eucas1p1.samsung.com>
2020-06-03 2:08 ` Martin Tournoij
2020-06-03 12:04 ` Peter Stephenson
2020-06-04 1:48 ` Daniel Shahaf
2020-06-04 2:43 ` Bart Schaefer
2020-06-04 4:06 ` Daniel Shahaf
2020-06-04 5:00 ` Bart Schaefer
2020-06-05 3:10 ` Daniel Shahaf
2020-06-05 3:18 ` Daniel Shahaf
2020-06-06 1:07 ` Bart Schaefer
2020-06-06 4:48 ` Daniel Shahaf [this message]
2020-06-06 7:04 ` Bart Schaefer
2020-06-04 6:31 ` Martin Tournoij
2020-06-05 2:22 ` Daniel Shahaf
2020-06-04 2:13 ` Vin Shelton
2020-06-04 2:35 ` Bart Schaefer
2020-06-04 2:36 ` Daniel Shahaf
2020-06-04 11:57 ` Vin Shelton
2020-06-04 5:06 ` Bart Schaefer
2020-06-04 5:41 ` Roman Perepelitsa
2020-06-05 2:07 ` Daniel Shahaf
2020-06-05 4:38 ` Roman Perepelitsa
2020-06-06 1:41 ` Bart Schaefer
2020-06-06 4:55 ` Daniel Shahaf
2020-06-06 6:25 ` Roman Perepelitsa
2020-06-06 7:08 ` Bart Schaefer
2020-06-06 8:03 ` Daniel Shahaf
[not found] ` <1941572212.466119.1591360860372@mail2.virginmedia.com>
[not found] ` <e7f7dfe2-eb4a-457b-85fb-091935a74c0e@www.fastmail.com>
2020-06-06 11:57 ` Peter Stephenson
2020-06-06 12:48 ` Roman Perepelitsa
2020-06-06 15:24 ` Bart Schaefer
2020-06-06 16:24 ` Peter Stephenson
2020-06-07 11:55 ` Daniel Shahaf
2020-06-07 17:00 ` Peter Stephenson
2020-06-08 3:27 ` Daniel Shahaf
2020-06-08 9:30 ` Peter Stephenson
2020-06-07 17:20 ` Bart Schaefer
2020-06-06 15:09 ` Bart Schaefer
2020-06-04 6:47 ` Martin Tournoij
2020-06-04 9:42 ` Peter Stephenson
2020-06-04 12:20 ` Roman Perepelitsa
2020-06-04 12:26 ` Peter Stephenson
2020-06-04 12:15 ` Peter Stephenson
2020-06-04 20:35 ` Bart Schaefer
2020-06-05 1:59 ` Daniel Shahaf
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=20200606044808.59509bdf@tarpaulin.shahaf.local2 \
--to=d.s@daniel.shahaf.name \
--cc=martin@arp242.net \
--cc=schaefer@brasslantern.com \
--cc=zsh-workers@zsh.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.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/zsh/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).