Hello Pavel,
> Just a nit, here should be (for readers):
>
> $ tar -c file | tar -t dir
Oops, thanks you. That's exactly what I mean.
> I don't like the '--ignore-missing' approach. That adds another
> non-symetric option to tar. We have the '--ignore-failed-read' option
> which works for archive creation and --ignore-missing works just for
> archive extraction.
How can we solve this? AFAIU you suggest something like reusing
--ignore-failed-read for the feature in question (correct me if I'm wrong).
But --ignore-failed-read is not exactly what I mean because:
1. it outputs a warning meaning "something unexpected happens":
$ tar --ignore-failed-read -cf /dev/null non-existing
tar: non-existing: Warning: Cannot stat: No such file or directory
$
2. according to the sources it means ignoring any read errors, not
only "existance" ones,
On the contrary, the suggested --ignore-missing suggests that:
1. missing member is expected so no warning is necessary when this
happens,
2. if a member exists but cannot be processed for some other reason,
an error must still be returned.
If I correctly understand you --ignore-missing can be modified to ignore
missing files on archive creation as well:
$ tar --ignore-failed-read -cf /dev/null non-existing
tar: non-existing: Warning: Cannot stat: No such file or directory
$ echo $?
0
$ tar --ignore-missing -cf /dev/null non-existing
$ echo $?
0
$
If a file exists and is unreadable for some other reason (e.g. permissions)
an error is still returned (unless using --ignore-failed-read) and a
warning/error is printed.
In this case there are questions:
1. Must --ignore-missing be applied to symlinks leading nowhere?
1.a. Must we also take into account --dereference?
2. Are there cases where --ignore-missing must be applied not only to files
provided on the command line/TAR_OPTIONS/-T?
3. (combination of 1. and 2.) How must tar behave if it finds a broken
symlink inside a directory provided on the command line?
IMHO,
1. no (unless --dereference is used, but it's case 1.a.),
1.a. uncertain, probably no (if a symlink exists it must reference an existing
file or an error is returned),
2. no,
3. it must behave as if --ignore-missing is not used.
It's just a quick thought. I have no use case for --ignore-missing during
archive creation right now so I might be wrong.
What do you think?
--
Vladimir A. Pavlov
