Misbehaving `--dryrun` flag in `az storage blob delete-batch`

[elibarzilay]

(Ubuntu, azure-cli 2.0.27, and showing storage as 2.0.25.)

I've tried playing with the new delete-batch, and could not figure out
how to use --if-modified-since or --if-unmodified-since -- no matter
what I did, it seems to always insist on deleting everything. After
lots of fiddling around, I used a new container just to experiment with,
and to my surprise, it looks like --dryrun just ignores these flags,
but when it's not used, there are not ignored (but have other, unrelated
issues).

If this is correct then this is a very bad problem, since it is common
to use a dry run flag to see what will be deleted, and ignoring these
flags means that I can end up deleting blobs unexpectedly.

[williexu]

The parameters are used to limit the operations according to whether the resource has been modified or not.
None of the batch commands take these parameters into account upon --dryrun.

--dryrun will simply list all blobs under consideration for deletion/upload.
This will always be a superset of the actual blobs that would be deleted/uploaded.
Only once the actual command is run will the properties be applied on a blob by blob basis.

[elibarzilay]

@williexu This is pretty bad in two ways:

1. It is a definition of "dry run" that is very different from any other
   use of the term. This should be made very clear in both the -h
   text and in the output that it produces because it's so unexpected.

2. There should be some way for people to do a proper dry run.
   Consider writing a script that purges old files: it is very common to
   write such a script in a dry run mode to verify that it would delete
   the correct blobs, and then just remove the dry run flag.

   If I understand it correctly, there is no way other than either
   creating a dummy container for testing (which is a major PITA, since
   there is no way to change the last-modified time, so it's a tedious
   process of copying files, waiting some time, etc).

[williexu]

@seguler If we want to do this, it would have to be done through server support for batch-commands.
The CLI simply passes the modified parameters to the service to process and cannot be done for a dryrun.

[arbaiti]

Hello,
I need to do cleanup of dump files on a blob container, and i don't know how to use this command.
I should delete dump older than 14 days.
Please if you have an example ?
Regards,

[williexu]

@arbaiti if you still need an example:

az storage blob delete-batch --source backups --if-unmodified-since `date -d "14 days  ago" '+%Y-%m-%dT%H:%MZ'`

[williexu]

Changing this issue to a service attention feature, as the CLI can only do so much to facilitate a dry-run if the service does not support this option.