Conversation

Notices

1. Embed this notice
   mcc (mcc@mastodon.social)'s status on Monday, 01-Jul-2024 01:16:40 JST mcc

   Is there a way to do `mv`, in either linux or Perl, that will fail if I try to copy a file over another file?

   In the mv manpage, I find a `-n` or `--no-clobber` option which does indeed refuse to replace file A with file B. But it is a silent failure. $? is 0 after I run an unsuccessful `mv -n`.

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Monday, 01-Jul-2024 03:57:17 JST mcc

     in reply to

     • lj·rk
     • Matthew Miller

     @mattdm @ljrk

     Paul Cantrell repeated this.
   • Embed this notice
     lj·rk (ljrk@todon.eu)'s status on Monday, 01-Jul-2024 03:57:17 JST lj·rk

     in reply to

     • Matthew Miller

     @mcc @mattdm

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:18 JST Matthew Miller

     in reply to

     • lj·rk

     @ljrk @mcc

     Anyway, everything is terrible.

     *switches to plan9*

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:18 JST Matthew Miller

     in reply to

     • lj·rk

     @ljrk @mcc

     Meanwhile on LWN... https://lwn.net/SubscriberLink/979524/f93c7f46307f3415/

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:19 JST Matthew Miller

     in reply to

     • lj·rk

     @ljrk @mcc

     Haven't tested, but I believe that's been fixed since 2015. From the release notes for 8.30 (2018):

     ``` 'mv -n A B' no longer suffers from a race condition that can
     overwrite a simultaneously-created B. This bug fix requires
     platform support for the renameat2 or renameatx_np syscalls, found
     in recent Linux and macOS kernels. As a side effect, 'mv -n A A'
     now silently does nothing if A exists.
     [bug introduced with coreutils-7.1]
     ```

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:19 JST Matthew Miller

     in reply to

     • lj·rk

     @ljrk @mcc

     Also this explains the `mv -n` silence when I tested on RHEL 7. :)

   • Embed this notice
     lj·rk (ljrk@todon.eu)'s status on Monday, 01-Jul-2024 03:57:20 JST lj·rk

     in reply to

     • Matthew Miller

     @mattdm @mcc Unfortunately `-n` doesn't seem to be race-free though :/

     https://unix.stackexchange.com/questions/248544/mv-move-file-only-if-destination-does-not-exist/248547?noredirect=1#comment428238_248547

     With that in mind (if still true), I don't see any worth in a `-n` flag (invoking the "it's not UNIX" meme here :D). Then again, while there are many very bad options added by the GNU project if you ask me (GNU/tar's --checkpoint-action flag springs to mind), but this'd be a really useful flag in principle.

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:21 JST Matthew Miller

     in reply to

     @mcc

     IMHO good for the coreutils maintainers for making some of this stuff make more sense after all of these years.

     But I'll wait for the "they hate Unix!" crowd to show up.

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:22 JST Matthew Miller

     in reply to

     @mcc

     Update to (at least) coreutils 9.2, or use a distro which provides that.

     With that version, mv -n will print an error and return 1 if a file is skipped. (Previously, it just printed nothing to indicate it was doing nothing. Insert Drake meme here.)

   • Embed this notice
     Matthew Miller (mattdm@hachyderm.io)'s status on Monday, 01-Jul-2024 03:57:22 JST Matthew Miller

     in reply to

     @mcc

     There is a new `--update none` option to get the old noclobber behavior, if you want it.

     tbh I'm surprised 1) they made what could be a breaking change and 2) to my knowledge there has been no "you broke my scripts" outcry. Although probably the second can be found if I look hard enough.

     Also, apparently posix only specifies -i and -f. Because, sure.