en/handbook/hb-working-use.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE sections SYSTEM "/dtd/book.dtd">

<!-- The content of this document is licensed under the CC-BY-SA license -->
<!-- See http://creativecommons.org/licenses/by-sa/1.0 -->

<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.24 2004/11/20 22:23:30 neysx Exp $ -->

<sections>

<version>1.22</version>
<date>2004-12-26</date>

<section>
<title>What are USE-flags?</title>
<subsection>
<title>The ideas behind USE-flags</title>
<body>

<p>
When you are installing Gentoo (or any other distribution, or even operating
system for that matter) you make choices depending on the environment you are 
working with. A setup for a server differs from a setup for a workstation.
A gaming workstation differs from a 3D rendering workstation.
</p>

<p>
This is not only true for choosing what packages you want to install, but also
what features a certain package should support. If you don't need OpenGL, why
would you bother installing OpenGL and build OpenGL support in most of your
packages? If you don't want to use KDE, why would you bother compiling packages
with KDE-support if those packages work flawlessly without?
</p>

<p>
To help users in deciding what to install/activate and what not, we wanted the
user to specify his/her environment in an easy way. This forces the user into
deciding what they really want and eases the process for Portage, our package
managment system, to make useful decisions.
</p>

</body>
</subsection>
<subsection>
<title>Definition of a USE-flag</title>
<body>

<p>
Enter the USE-flags. Such a flag is a keyword that embodies support and
dependency-information for a certain concept. If you define a certain USE-flag, 
Portage will know that you want support for the chosen keyword. Of course
this also alters the dependency information for a package.
</p>

<p>
Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
have this keyword in your <c>USE</c> variable, all packages that have
<e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
packages that have an <e>optional</e> KDE dependency will be installed
<e>without</e> installing the KDE libraries (as dependency). If you have defined
the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
support, and the KDE libraries will be installed as dependency.
</p>

<p>
By correctly defining the keywords you will receive a system tailored
specifically to your needs.
</p>

</body>
</subsection>
<subsection>
<title>What USE-flags exist?</title>
<body>

<p>
There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
</p>

<ul>
  <li>
    A <e>global</e> USE-flag is used by several packages, system-wide. This is 
    what most people see as USE-flags.
  </li>
  <li>
    A <e>local</e> USE-flag is used by a single package to make package-specific
    decisions.
  </li>
</ul>

<p>
A list of available global USE-flags can be found <uri
link="/dyn/use-index.xml">online</uri> or locally in
<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
snippet:
</p>

<pre caption="A short snippet of available USE-flags">
gtk     - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
gtk2    - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
gtkhtml - Adds support for gnome-extra/gtkhtml
guile   - Adds support for dev-util/guile (interpreter for Scheme)
icc     - Use the Intel C++ Compiler if the package supports it
icc-pgo - Enable PGO data generation or use when use icc.
imap    - Adds support for IMAP
</pre>

<p>
A list of available local USE-flags can be found locally in
<path>/usr/portage/profiles/use.local.desc</path>.
</p>

</body>
</subsection>
</section>
<section>
<title>Using USE-flags</title>
<subsection>
<title>Declare permanent USE-flags</title>
<body>

<p>
In the hope you are convinced of the importance of USE-flags we will now inform
you how to declare USE-flags.
</p>

<p>
As previously mentioned, all USE-flags are declared inside the <c>USE</c>
variable. To make it easy for users to search and pick USE-flags, we already
provide a <e>default</e> USE setting. This setting is a collection of USE-flags
we think are commonly used by the Gentoo users. This default setting is declared
in the <path>make.defaults</path> files part of your profile. Let us take a 
look at this default setting:
</p>

<pre caption="/usr/portage/profiles/default-linux/x86/2004.3/make.defaults USE variable">
<comment>(This is an example and might have changed since it was taken)</comment>
USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
     gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
     nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
     slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
</pre>

<p>
As you can see, this variable already contains quite a lot of keywords. Do
<b>not</b> alter any <path>make.defaults</path> file to tailor
the <c>USE</c> variable to your needs: changes in this file will be undone when
you update Portage!
</p>

<p>
To change this default setting, you need to add or remove keywords to the
<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable 
in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
require, or remove the USE-flags you don't want. This latter is done by
prefixing the keyword with the minus-sign ("-").
</p>

<p>
For instance, to remove support for KDE and QT but add support for ldap, the
following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
</p>

<pre caption="An example USE setting in /etc/make.conf">
USE="-kde -qt ldap"
</pre>

</body>
</subsection>
<subsection>
<title>Declaring USE flags for individual packages</title>
<body>

<p>
Sometimes you want to declare a certain USE flag for one (or a couple) of
applications but not system-wide. To accomplish this, you will need to create
the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
<path>/etc/portage/package.use</path>.
</p>

<p>
For instance, if you don't want <c>berkdb</c> support globally but you do want
it for <c>mysql</c>, you would add:
</p>

<pre caption="/etc/portage/package.use example">
dev-db/mysql berkdb
</pre>

<p>
You can of course also explicitly <e>disable</e> USE flags for a certain
application. For instance, if you don't want <c>java</c> support in PHP:
</p>

<pre caption="/etc/portage/package.use 2nd example">
dev-php/php -java
</pre>

</body>
</subsection>
<subsection>
<title>Declare temporary USE-flags</title>
<body>

<p>
Sometimes you want to set a certain USE-setting only once. Instead of editing
<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just 
declare the USE-variable as environment variable. Remember that, when you
re-emerge or update this application (either explicitly or as part of a system 
update) your changes will be lost!
</p>

<p>
As an example we will temporarily remove java from the USE-setting
during the installation of mozilla.
</p>

<pre caption="Using USE as environment variable">
# <i>USE="-java" emerge mozilla</i>
</pre>

</body>
</subsection>
<subsection>
<title>Inheriting USE-flags</title>
<body>

<p>
Some packages don't only listen to USE-flags, but also provide USE-flags. When
you install such a package, the USE-flag they provide is added to your USE
setting. To view the list of packages that provide a USE-flag, check
<path>/etc/make.profile/use.defaults</path>:
</p>

<pre caption="A snippet from /etc/make.profile/use.defaults">
gnome           gnome-base/gnome
gtk             x11-libs/gtk+
qt              x11-libs/qt
kde             kde-base/kdebase
motif           x11-libs/openmotif
</pre>

</body>
</subsection>
<subsection>
<title>Precedence</title>
<body>

<p>
Of course there is a certain precedence on what setting has priority over the
USE setting. You don't want to declare <c>USE="-java"</c> only to see that
<c>java</c> is declared anyway. The precedence for the USE setting is, ordered
by priority (first has lowest priority):
</p>

<ol>
  <li>
    Default USE setting declared in the <path>make.defaults</path> files part of
    your profile
  </li>
  <li>
    Inherited USE setting if a package from
    <path>/etc/make.profile/use.defaults</path> is installed
  </li>
  <li>
    User-defined USE setting in <path>/etc/make.conf</path>
  </li>
  <li>
    User-defined USE setting in <path>/etc/portage/package.use</path>
  </li>
  <li>
    User-defined USE setting as environment variable
  </li>
</ol>

<p>
To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
This will list all relevant variables (including the <c>USE</c> variable) with
the content used by Portage.
</p>

<pre caption="Running emerge info">
# <i>emerge info</i>
</pre>

</body>
</subsection>
<subsection>
<title>Adapting your Entire System to New USE Flags</title>
<body>

<p>
If you have altered your USE flags and you wish to update your entire system to
use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
</p>

<pre caption="Rebuilding your entire system">
# <i>emerge --update --deep --newuse world</i>
</pre>

<p>
Next, run Portage's depclean to remove the conditional dependencies that
were emerged on your "old" system but that have been obsoleted by the new USE
flags. 
</p>

<warn>
Running <c>emerge depclean</c> is a dangerous operation and should be handled
with care. Double-check the provided list of "obsoleted" packages to make sure
it doesn't remove packages you need. In the following example we add the
<c>-p</c> switch to have depclean only list the packages without removing them.
</warn>

<pre caption="Removing obsoleted packages">
# <i>emerge -p depclean</i>
</pre>

<p>
When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
applications that are dynamically linked against shared objects provided by 
possibly removed packages. <c>revdep-rebuild</c> is part of the 
<c>gentoolkit</c> package; don't forget to emerge it first.
</p>

<pre caption="Running revdep-rebuild">
# <i>revdep-rebuild</i>
</pre>

<p>
When all this is accomplished, your system is using the new USE flag settings.
</p>

</body>
</subsection>
</section>
<section>
<title>Package specific USE-flags</title>
<subsection>
<title>Viewing available USE-flags</title>
<body>

<p>
Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
options:
</p>

<pre caption="Viewing the used USE-flags">
# <i>emerge --pretend --verbose mozilla</i>
These are the packages that I would merge, in order:

Calculating dependencies ...done!
[ebuild  N    ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap 
+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
-moznocompose -moznoxft 
</pre>

<p>
<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
dedicated to package information called <c>etcat</c> which resides in the
<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
</p>

<pre caption="Installing gentoolkit">
# <i>emerge gentoolkit</i>
</pre>

<p>
Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
certain package. For instance, for the <c>gnumeric</c> package:
</p>

<pre caption="Using etcat to view used USE-flags">
# <i>etcat uses gnumeric</i>
[ Colour Code : <i>set</i> <comment>unset</comment> ]
[ Legend      : (U) Col 1 - Current USE flags        ]
[             : (I) Col 2 - Installed With USE flags ]

 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
 - - <comment>libgda</comment>  : Adds GNU Data Access (CORBA wrapper) support for gnumeric
 - - <comment>gnomedb</comment> : unknown
 + + <i>python</i>  : Adds support/bindings for the Python language
 + + <i>bonobo</i>  : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
</pre>

</body>
</subsection>
</section>
</sections>
1	swift	1.7	<?xml version='1.0' encoding='UTF-8'?>
2			<!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4	swift	1.1	<!-- The content of this document is licensed under the CC-BY-SA license -->
5			<!-- See http://creativecommons.org/licenses/by-sa/1.0 -->
6
7	swift	1.25	<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.24 2004/11/20 22:23:30 neysx Exp $ -->
8	swift	1.1
9			<sections>
10	swift	1.22
11	swift	1.25	<version>1.22</version>
12			<date>2004-12-26</date>
13	swift	1.22
14	swift	1.1	<section>
15			<title>What are USE-flags?</title>
16			<subsection>
17			<title>The ideas behind USE-flags</title>
18			<body>
19
20	swift	1.2	<p>
21			When you are installing Gentoo (or any other distribution, or even operating
22			system for that matter) you make choices depending on the environment you are
23			working with. A setup for a server differs from a setup for a workstation.
24			A gaming workstation differs from a 3D rendering workstation.
25			</p>
26
27			<p>
28			This is not only true for choosing what packages you want to install, but also
29			what features a certain package should support. If you don't need OpenGL, why
30			would you bother installing OpenGL and build OpenGL support in most of your
31			packages? If you don't want to use KDE, why would you bother compiling packages
32	swift	1.5	with KDE-support if those packages work flawlessly without?
33	swift	1.2	</p>
34
35			<p>
36			To help users in deciding what to install/activate and what not, we wanted the
37	swift	1.10	user to specify his/her environment in an easy way. This forces the user into
38	swift	1.11	deciding what they really want and eases the process for Portage, our package
39	swift	1.5	managment system, to make useful decisions.
40	swift	1.2	</p>
41
42	swift	1.1	</body>
43			</subsection>
44			<subsection>
45			<title>Definition of a USE-flag</title>
46			<body>
47
48	swift	1.2	<p>
49			Enter the USE-flags. Such a flag is a keyword that embodies support and
50			dependency-information for a certain concept. If you define a certain USE-flag,
51	swift	1.3	Portage will know that you want support for the chosen keyword. Of course
52	swift	1.2	this also alters the dependency information for a package.
53			</p>
54
55			<p>
56	swift	1.6	Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
57	swift	1.2	have this keyword in your <c>USE</c> variable, all packages that have
58			<e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
59			packages that have an <e>optional</e> KDE dependency will be installed
60			<e>without</e> installing the KDE libraries (as dependency). If you have defined
61			the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
62			support, and the KDE libraries will be installed as dependency.
63			</p>
64
65			<p>
66			By correctly defining the keywords you will receive a system tailored
67			specifically to your needs.
68			</p>
69
70	swift	1.1	</body>
71			</subsection>
72			<subsection>
73			<title>What USE-flags exist?</title>
74			<body>
75
76	swift	1.2	<p>
77			There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
78			</p>
79
80			<ul>
81			<li>
82			A <e>global</e> USE-flag is used by several packages, system-wide. This is
83			what most people see as USE-flags.
84			</li>
85			<li>
86	swift	1.8	A <e>local</e> USE-flag is used by a single package to make package-specific
87	swift	1.2	decisions.
88			</li>
89			</ul>
90
91			<p>
92			A list of available global USE-flags can be found <uri
93			link="/dyn/use-index.xml">online</uri> or locally in
94			<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
95			snippet:
96			</p>
97
98			<pre caption="A short snippet of available USE-flags">
99			gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
100			gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
101			gtkhtml - Adds support for gnome-extra/gtkhtml
102			guile - Adds support for dev-util/guile (interpreter for Scheme)
103			icc - Use the Intel C++ Compiler if the package supports it
104			icc-pgo - Enable PGO data generation or use when use icc.
105			imap - Adds support for IMAP
106			</pre>
107
108	swift	1.18	<p>
109			A list of available local USE-flags can be found locally in
110			<path>/usr/portage/profiles/use.local.desc</path>.
111			</p>
112
113	swift	1.1	</body>
114			</subsection>
115			</section>
116			<section>
117			<title>Using USE-flags</title>
118			<subsection>
119			<title>Declare permanent USE-flags</title>
120			<body>
121
122	swift	1.2	<p>
123			In the hope you are convinced of the importance of USE-flags we will now inform
124			you how to declare USE-flags.
125			</p>
126
127			<p>
128			As previously mentioned, all USE-flags are declared inside the <c>USE</c>
129			variable. To make it easy for users to search and pick USE-flags, we already
130			provide a <e>default</e> USE setting. This setting is a collection of USE-flags
131			we think are commonly used by the Gentoo users. This default setting is declared
132	swift	1.25	in the <path>make.defaults</path> files part of your profile. Let us take a
133			look at this default setting:
134	swift	1.2	</p>
135
136	swift	1.25	<pre caption="/usr/portage/profiles/default-linux/x86/2004.3/make.defaults USE variable">
137			<comment>(This is an example and might have changed since it was taken)</comment>
138	neysx	1.14	USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
139			gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
140			nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
141			slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
142	swift	1.2	</pre>
143
144			<p>
145			As you can see, this variable already contains quite a lot of keywords. Do
146	swift	1.25	<b>not</b> alter any <path>make.defaults</path> file to tailor
147	swift	1.2	the <c>USE</c> variable to your needs: changes in this file will be undone when
148			you update Portage!
149			</p>
150
151			<p>
152			To change this default setting, you need to add or remove keywords to the
153			<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
154			in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
155			require, or remove the USE-flags you don't want. This latter is done by
156			prefixing the keyword with the minus-sign ("-").
157			</p>
158
159			<p>
160			For instance, to remove support for KDE and QT but add support for ldap, the
161			following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
162			</p>
163
164			<pre caption="An example USE setting in /etc/make.conf">
165			USE="-kde -qt ldap"
166			</pre>
167
168	swift	1.19	</body>
169			</subsection>
170			<subsection>
171			<title>Declaring USE flags for individual packages</title>
172			<body>
173
174	swift	1.17	<p>
175			Sometimes you want to declare a certain USE flag for one (or a couple) of
176			applications but not system-wide. To accomplish this, you will need to create
177			the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
178			<path>/etc/portage/package.use</path>.
179			</p>
180
181			<p>
182			For instance, if you don't want <c>berkdb</c> support globally but you do want
183			it for <c>mysql</c>, you would add:
184			</p>
185
186			<pre caption="/etc/portage/package.use example">
187			dev-db/mysql berkdb
188			</pre>
189
190			<p>
191			You can of course also explicitly <e>disable</e> USE flags for a certain
192			application. For instance, if you don't want <c>java</c> support in PHP:
193			</p>
194
195			<pre caption="/etc/portage/package.use 2nd example">
196			dev-php/php -java
197			</pre>
198
199	swift	1.1	</body>
200			</subsection>
201			<subsection>
202			<title>Declare temporary USE-flags</title>
203			<body>
204
205	swift	1.2	<p>
206			Sometimes you want to set a certain USE-setting only once. Instead of editing
207			<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
208	swift	1.17	declare the USE-variable as environment variable. Remember that, when you
209			re-emerge or update this application (either explicitly or as part of a system
210			update) your changes will be lost!
211	swift	1.2	</p>
212
213			<p>
214			As an example we will temporarily remove java from the USE-setting
215			during the installation of mozilla.
216			</p>
217
218	swift	1.13	<pre caption="Using USE as environment variable">
219	swift	1.2	# <i>USE="-java" emerge mozilla</i>
220			</pre>
221
222	swift	1.1	</body>
223			</subsection>
224			<subsection>
225			<title>Inheriting USE-flags</title>
226			<body>
227
228	swift	1.2	<p>
229			Some packages don't only listen to USE-flags, but also provide USE-flags. When
230			you install such a package, the USE-flag they provide is added to your USE
231			setting. To view the list of packages that provide a USE-flag, check
232			<path>/etc/make.profile/use.defaults</path>:
233			</p>
234
235			<pre caption="A snippet from /etc/make.profile/use.defaults">
236			gnome gnome-base/gnome
237			gtk x11-libs/gtk+
238			qt x11-libs/qt
239			kde kde-base/kdebase
240			motif x11-libs/openmotif
241			</pre>
242
243			</body>
244			</subsection>
245			<subsection>
246	swift	1.15	<title>Precedence</title>
247	swift	1.2	<body>
248
249			<p>
250	neysx	1.16	Of course there is a certain precedence on what setting has priority over the
251	swift	1.2	USE setting. You don't want to declare <c>USE="-java"</c> only to see that
252			<c>java</c> is declared anyway. The precedence for the USE setting is, ordered
253			by priority (first has lowest priority):
254			</p>
255
256			<ol>
257			<li>
258	swift	1.25	Default USE setting declared in the <path>make.defaults</path> files part of
259			your profile
260	swift	1.2	</li>
261			<li>
262			Inherited USE setting if a package from
263			<path>/etc/make.profile/use.defaults</path> is installed
264			</li>
265			<li>
266			User-defined USE setting in <path>/etc/make.conf</path>
267			</li>
268			<li>
269	swift	1.17	User-defined USE setting in <path>/etc/portage/package.use</path>
270			</li>
271			<li>
272	swift	1.2	User-defined USE setting as environment variable
273			</li>
274			</ol>
275	swift	1.4
276			<p>
277			To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
278			This will list all relevant variables (including the <c>USE</c> variable) with
279			the content used by Portage.
280			</p>
281
282			<pre caption="Running emerge info">
283			# <i>emerge info</i>
284			</pre>
285	swift	1.2
286	swift	1.1	</body>
287			</subsection>
288	swift	1.12	<subsection>
289			<title>Adapting your Entire System to New USE Flags</title>
290			<body>
291
292			<p>
293			If you have altered your USE flags and you wish to update your entire system to
294	swift	1.21	use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
295	swift	1.12	</p>
296
297			<pre caption="Rebuilding your entire system">
298	swift	1.21	# <i>emerge --update --deep --newuse world</i>
299	swift	1.12	</pre>
300
301			<p>
302	swift	1.20	Next, run Portage's depclean to remove the conditional dependencies that
303	swift	1.12	were emerged on your "old" system but that have been obsoleted by the new USE
304			flags.
305			</p>
306
307			<warn>
308			Running <c>emerge depclean</c> is a dangerous operation and should be handled
309			with care. Double-check the provided list of "obsoleted" packages to make sure
310			it doesn't remove packages you need. In the following example we add the
311			<c>-p</c> switch to have depclean only list the packages without removing them.
312			</warn>
313
314			<pre caption="Removing obsoleted packages">
315			# <i>emerge -p depclean</i>
316			</pre>
317
318			<p>
319	swift	1.21	When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
320			applications that are dynamically linked against shared objects provided by
321			possibly removed packages. <c>revdep-rebuild</c> is part of the
322			<c>gentoolkit</c> package; don't forget to emerge it first.
323			</p>
324
325			<pre caption="Running revdep-rebuild">
326			# <i>revdep-rebuild</i>
327			</pre>
328
329			<p>
330			When all this is accomplished, your system is using the new USE flag settings.
331	swift	1.12	</p>
332
333			</body>
334			</subsection>
335	swift	1.1	</section>
336			<section>
337			<title>Package specific USE-flags</title>
338			<subsection>
339	swift	1.2	<title>Viewing available USE-flags</title>
340	swift	1.1	<body>
341	swift	1.2
342			<p>
343			Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
344	swift	1.21	find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
345			options:
346	swift	1.2	</p>
347
348			<pre caption="Viewing the used USE-flags">
349			# <i>emerge --pretend --verbose mozilla</i>
350			These are the packages that I would merge, in order:
351
352			Calculating dependencies ...done!
353			[ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
354			+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
355			-moznocompose -moznoxft
356			</pre>
357
358			<p>
359			<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
360			dedicated to package information called <c>etcat</c> which resides in the
361			<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
362			</p>
363
364			<pre caption="Installing gentoolkit">
365	swift	1.21	# <i>emerge gentoolkit</i>
366	swift	1.2	</pre>
367
368			<p>
369			Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
370			certain package. For instance, for the <c>gnumeric</c> package:
371			</p>
372
373			<pre caption="Using etcat to view used USE-flags">
374			# <i>etcat uses gnumeric</i>
375			[ Colour Code : <i>set</i> <comment>unset</comment> ]
376			[ Legend : (U) Col 1 - Current USE flags ]
377			[ : (I) Col 2 - Installed With USE flags ]
378
379			U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
380			- - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
381			- - <comment>gnomedb</comment> : unknown
382			+ + <i>python</i> : Adds support/bindings for the Python language
383			+ + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
384			</pre>
385	swift	1.1
386			</body>
387			</subsection>
388			</section>
389			</sections>