On Thu, Nov 16, 2017 at 2:37 AM, Bruno Haible <br...@clisp.org> wrote:
> Paul Eggert wrote:
>> > + ln -f "$file" "$file~" 2>/dev/null || cp -f "$file" "$file~" || {
>>
>> This will be problematic if the destination already exists, as the
>> resulting permissions etc. may not be what the user intend. How about if
>> we fall back on "mv -f" instead? Although this has the disadvantage of
>> having a small window where "$file" does not exist, I think that's
>> preferable to the disadvantage of using "cp".
>
> How about
>
> ln -f "$file" "$file~" 2>/dev/null || { rm -f "$file~" && cp "$file"
> "$file~"; } || {
>
> then? It fixes the problem "if the destination already exists", and does
> NOT leave a window where "$file" does not exist.
Which is more important? (tempered with qualification that it probably
doesn't matter at all, since this is in the context of running a
program (gzexe) that is used very rarely, and even less frequently in
a context where ln fails to create a hard link):
- preserving backup file metadata (that backup may end up being the
sole copy of the original)
- ensuring that the specified name does not go missing briefly
Given that the backup file may be the only remaining copy of the
original, I prefer the risk of an ephemeral ENOENT, so that we can
guarantee the running of gzexe does not destroy any file metadata.
