Extracting from archive | compressing to new archive

Shell Programming and Scripting
1

Hi there,

I have one huge archive (it's a system image).
I need sometime to create smaller archives with only one or two file from my big archive.
So I'm looking for a command that extracts files from an archive and pipe them to another one.
I tried the following :

tar -xzOf oldarchive.tgz ./file1 ./file2 | tar -czf newarchive.tgz

But it doesn't seem to work: it says:

tar: Cowardly refusing to create an empty archive

Can anybody explain me why?
Does anybody have a better idea?

Thanks for your help.
Santiago

2

i couldnt understand why you used '0' in the code in '-xz0f'. I think it would work even if u dont use it in the first place. Try that out.

3

Hey bdiwakarteja,
And thx for your interest.
-O means output to stdout instead of a file.
I thought it was necessary to redirect to another archive.
I can't try without it right now but I will do it asap.
Thx for your help
Santiago

4

The problem is that tar can't archive files from stdin, only when they're given as arguments on the command line. I'm afraid you won't get around extracting the 2 files, and then tar'ing them again.

5

Thanks pludi for your help.
This is a bit anoying because I'm not the administrator of the machine.
But the big archive contains files owned by root that are meant to be used for computers that I administrate.
So if I extract them to the filesystem before tar'ing them again, they will be owned by me and not root anymore.
Does anybody thinks of a way to get around the problem?
Thanks for your help

6

Well, with -O you'd have lost the permissions anyways, as those can only be bound to a file, not to a stream. So IMO your best chance would be to extract the 2 files, move them to a machine you administer, and then create a new archive from them after you've corrected the permissions.