Selective update with pacman / yaourt?

I´m using yaourt in ArchLinux.

• Is it possible to do a yaourt -Syu but only including packages from core/extra or what I want?
• How to update single packages? yaourt -U <package> does not work (could not find or read package). Do I have to use yaourt -S <package>?

EDIT

• There is a problem with using yaourt -S <package>: If there is no update available, the package will be reinstalled anyway
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For the first point:

Is it possible to do a yaourt -Syu but only including packages from core/extra or what I want?

According to the documentation, pacman (or yaourt in this case) will attempt to read pacman.conf each time it is invoked. So, did you try to comment the sections you don't want to be upgraded?

For the second point:

How to update single packages? yaourt -U <package> does not work (could not find or read package). Do I have to use yaourt -S <package>?

Pacman's install command -S it's, in fact, a synchronization. Installing or upgrading are done in the same way:

$pacman -S <package>  Or: $ yaourt -S <package>

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Ok, but with selective update I meant giving the selection in the command line when doing the update. –  user905686 May 23 '12 at 13:00