Remove a path prefix on backup and/or restore

[danwilliams]

Attic uses the full path to back up. This is not always useful or wanted. In many cases I might be backing up the contents of a user's home directory, or files for a website or application, which may later be restored to a different path. In those cases, the absolute path is not only irrelevant, but annoying - it should be possible to extract at any point, from any backup set, consistently, regardless of path changes that may have happened in between (e.g. a website moving to a different server and having a different base path).

I would not mind there being some kind of warning when backing up or restoring a set which uses relative paths - perhaps, though, this would only be needed if extracting the backup to the filesystem root (i.e. /). Otherwise, it should be assumed that the user has read the manual and is using the relative path options because they know how to.

_Comparison note__: Bup allows this sort of thing, e.g. most usefully through its --graft option._

[barsanuphe]

I agree that I expected to back up a directory's contents, not where this directory is in the specific machine the backup is made. It makes extracting on another machine with different users clunky.

I think an option equivalent of bup's --strip-path would be sufficient.

[ThomasWaldmann]

I use to assemble all useful filesystems under /rootfs using "mount --bind /real /rootfs/real" before backing up (so that I can get rid of /sys /dev /proc vfs and even get the files that reside on-disk on the root fs for /dev that are usually hidden by the vfs mounted over them).

Also, it is a bit unpretty to have always /rootfs/... filenames in the backup and in the exclude list as this is only a backup implementation detail.

[fcartegnie]

This bug is duplicate of #109

[ThomasWaldmann]

@fcartegnie your link is wrong. Also, only link to duplicates within same project.