This week we want to explain a new Portage option which allows you to track changes to USE flag settings you may have altered after installing an application. We're talking about --newuse, one of a number of very useful new features in Portage 2.0.51. Before we start, make sure that you've installed the latest Portage revision on your box.
Imagine that up until today, you never had printer. Now you bought one, and of course you want to use your Gentoo system to test your new printer. First of all, you'd want printing support for some of the applications you've installed. In order to get that you would alter your USE flags and add cups and maybe some more flags to your USE variable in /etc/make.conf.
So what's next, then? You'll need to find an easy way to create a listing with all packages affected by this USE flag change:
Type emerge --newuse to list all packages affected by a USE flag change:
Code Listing 1: List all packages affected by a USE flag change
# emerge --newuse world -Dpv These are the packages that I would merge, in order: Calculating world dependencies ...done! [ebuild N ] net-print/cups-1.1.21-r2 -debug +pam -samba -slp +ssl 8,348 kB [ebuild R ] gnome-base/nautilus-2.8.0 +cups* -debug -flac -gstreamer -mad +oggvorbis 5,637 kB
No surprise that the CUPS package itself wants to get installed now, but you will also notice the appended asterisk to the +cups USE flag on the Nautilus package: This simply points out that the USE flag has changed, and you can now merge CUPS and all the packages which could benefit from an active cups USE flag. Don't forget to configure your new printer.
from http://www.gentoo.org/news/en/gwn/20041025-newsletter.xml