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<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE sections SYSTEM "/dtd/book.dtd">
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<!-- The content of this document is licensed under the CC-BY-SA license -->
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<!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-variables.xml,v 1.17 2006/03/14 19:29:29 neysx Exp $ -->
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<sections>
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<version>1.13</version>
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<date>2005-09-28</date>
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<section>
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<title>Environment Variables?</title>
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<subsection>
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<title>What they are</title>
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<body>
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<p>
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An environment variable is a named object that contains information used by one
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or more applications. Many users (and especially those new to Linux) find this
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a bit weird or unmanageable. However, this is a mistake: by using environment
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variables one can easily change a configuration setting for one or more
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applications.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>Important Examples</title>
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<body>
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<p>
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The following table lists a number of variables used by a Linux system and
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describes their use. Example values are presented after the table.
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</p>
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<table>
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<tr>
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<th>Variable</th>
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<th>Description</th>
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</tr>
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<tr>
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<ti>PATH</ti>
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<ti>
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This variable contains a colon-separated list of directories in which your
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system looks for executable files. If you enter a name of an executable
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(such as <c>ls</c>, <c>rc-update</c> or <c>emerge</c>) but this executable
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is not located in a listed directory, your system will not execute it
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(unless you enter the full path as command, such as <c>/bin/ls</c>).
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</ti>
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</tr>
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<tr>
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<ti>ROOTPATH</ti>
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<ti>
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This variable has the same function as <c>PATH</c>, but this one only lists
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the directories that should be checked when the root-user enters a command.
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</ti>
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</tr>
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<tr>
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<ti>LDPATH</ti>
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<ti>
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This variable contains a colon-separated list of directories in which the
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dynamical linker searches through to find a library.
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</ti>
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</tr>
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<tr>
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<ti>MANPATH</ti>
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<ti>
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This variable contains a colon-separated list of directories in which the
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<c>man</c> command searches for the man pages.
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</ti>
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</tr>
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<tr>
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<ti>INFODIR</ti>
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<ti>
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This variable contains a colon-separated list of directories in which the
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<c>info</c> command searches for the info pages.
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</ti>
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</tr>
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<tr>
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<ti>PAGER</ti>
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<ti>
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This variable contains the path to the program used to list the contents of
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files through (such as <c>less</c> or <c>more</c>).
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</ti>
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</tr>
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<tr>
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<ti>EDITOR</ti>
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<ti>
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This variable contains the path to the program used to change the contents
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of files with (such as <c>nano</c> or <c>vi</c>).
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</ti>
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</tr>
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<tr>
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<ti>KDEDIRS</ti>
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<ti>
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This variable contains a colon-separated list of directories which contain
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KDE-specific material.
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</ti>
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</tr>
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<tr>
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<ti>CLASSPATH</ti>
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<ti>
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This variable contains a colon-separated list of directories which contain
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Java classes.
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</ti>
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</tr>
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<tr>
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<ti>CONFIG_PROTECT</ti>
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<ti>
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This variable contains a <e>space</e>-delimited list of directories which
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should be protected by Portage during updates.
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</ti>
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</tr>
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<tr>
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<ti>CONFIG_PROTECT_MASK</ti>
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<ti>
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This variable contains a <e>space</e>-delimited list of directories which
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should not be protected by Portage during updates.
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</ti>
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</tr>
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</table>
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<p>
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Below you will find an example definition of all these variables:
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</p>
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<pre caption="Example definitions">
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PATH="/bin:/usr/bin:/usr/local/bin:/opt/bin:/usr/games/bin"
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ROOTPATH="/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin"
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LDPATH="/lib:/usr/lib:/usr/local/lib:/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3"
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MANPATH="/usr/share/man:/usr/local/share/man"
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INFODIR="/usr/share/info:/usr/local/share/info"
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PAGER="/usr/bin/less"
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EDITOR="/usr/bin/vim"
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KDEDIRS="/usr"
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CLASSPATH="/opt/blackdown-jre-1.4.1/lib/rt.jar:."
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CONFIG_PROTECT="/usr/X11R6/lib/X11/xkb /opt/tomcat/conf \
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/usr/kde/3.1/share/config /usr/share/texmf/tex/generic/config/ \
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/usr/share/texmf/tex/platex/config/ /usr/share/config"
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CONFIG_PROTECT_MASK="/etc/gconf"
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</pre>
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</body>
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</subsection>
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</section>
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<section>
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<title>Defining Variables Globally</title>
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<subsection>
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<title>The /etc/env.d Directory</title>
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<body>
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<p>
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To centralise the definitions of these variables, Gentoo introduced the
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<path>/etc/env.d</path> directory. Inside this directory you will find a number
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of files, such as <path>00basic</path>, <path>05gcc</path>, etc. which contain
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the variables needed by the application mentioned in their name.
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</p>
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<p>
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For instance, when you installed <c>gcc</c>, a file called <path>05gcc</path>
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was created by the ebuild which contains the definitions of the following
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variables:
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</p>
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<pre caption="/etc/env.d/05gcc">
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PATH="/usr/i686-pc-linux-gnu/gcc-bin/3.2"
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ROOTPATH="/usr/i686-pc-linux-gnu/gcc-bin/3.2"
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MANPATH="/usr/share/gcc-data/i686-pc-linux-gnu/3.2/man"
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INFOPATH="/usr/share/gcc-data/i686-pc-linux-gnu/3.2/info"
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CC="gcc"
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CXX="g++"
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LDPATH="/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3"
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</pre>
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<p>
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Other distributions tell you to change or add such environment variable
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definitions in <path>/etc/profile</path> or other locations. Gentoo on the other
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hand makes it easy for you (and for Portage) to maintain and manage the
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environment variables without having to pay attention to the numerous files that
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can contain environment variables.
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</p>
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<p>
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For instance, when <c>gcc</c> is updated, the <path>/etc/env.d/05gcc</path> file
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is updated too without requesting any user-interaction.
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</p>
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<p>
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This not only benefits Portage, but also you, as user. Occasionally you might
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be asked to set a certain environment variable system-wide. As an example we
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take the <c>http_proxy</c> variable. Instead of messing about with
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<path>/etc/profile</path>, you can now just create a file
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(<path>/etc/env.d/99local</path>) and enter your definition(s) in it:
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</p>
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<pre caption="/etc/env.d/99local">
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http_proxy="proxy.server.com:8080"
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</pre>
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<p>
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By using the same file for all your variables, you have a quick overview on the
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variables you have defined yourself.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>The env-update Script</title>
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<body>
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<p>
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Several files in <path>/etc/env.d</path> define the <c>PATH</c> variable. This
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is not a mistake: when you run <c>env-update</c>, it will append the several
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definitions before it updates the environment variables, thereby making it easy
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for packages (or users) to add their own environment variable settings without
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interfering with the already existing values.
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</p>
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<p>
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The <c>env-update</c> script will append the values in the alphabetical order
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of the <path>/etc/env.d</path> files. The file names must begin with two
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decimal digits.
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</p>
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<pre caption="Update order used by env-update">
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00basic 99kde-env 99local
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+-------------+----------------+-------------+
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PATH="/bin:/usr/bin:/usr/kde/3.2/bin:/usr/local/bin"
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</pre>
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<p>
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The concatenation of variables does not always happen, only with the following
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variables: <c>KDEDIRS</c>, <c>PATH</c>, <c>CLASSPATH</c>, <c>LDPATH</c>,
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<c>MANPATH</c>, <c>INFODIR</c>, <c>INFOPATH</c>, <c>ROOTPATH</c>,
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<c>CONFIG_PROTECT</c>, <c>CONFIG_PROTECT_MASK</c>, <c>PRELINK_PATH</c> and
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<c>PRELINK_PATH_MASK</c>. For all other variables the latest defined value (in
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alphabetical order of the files in <path>/etc/env.d</path>) is used.
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</p>
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<p>
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When you run <c>env-update</c>, the script will create all environment variables
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and place them in <path>/etc/profile.env</path> (which is used by
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<path>/etc/profile</path>). It will also extract the information from the
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<c>LDPATH</c> variable and use that to create <path>/etc/ld.so.conf</path>.
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After this, it will run <c>ldconfig</c> to recreate the
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<path>/etc/ld.so.cache</path> file used by the dynamical linker.
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</p>
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<p>
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If you want to notice the effect of <c>env-update</c> immediately after you run
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it, execute the following command to update your environment. Users who have
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installed Gentoo themselves will probably remember this from the installation
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instructions:
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</p>
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<pre caption="Updating the environment">
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# <i>env-update && source /etc/profile</i>
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</pre>
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<note>
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The above command only updates the variables in your current terminal,
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<e>new</e> consoles, and their children. Thus, if you are working in X11, you
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will need to either type <c>source /etc/profile</c> in every new terminal you
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open or restart X so that all new terminals source the new variables. If you
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use a login manager, become root and type <c>/etc/init.d/xdm restart</c>. If
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not, you will need to logout and log back in for X to spawn children with the
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new variable values.
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</note>
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</body>
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</subsection>
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</section>
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<section>
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<title>Defining Variables Locally</title>
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<subsection>
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<title>User Specific</title>
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<body>
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<p>
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You do not always want to define an environment variable globally. For instance,
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you might want to add <path>/home/my_user/bin</path> and the current working
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directory (the directory you are in) to the <c>PATH</c> variable
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but don't want all other users on your system to have that in their <c>PATH</c>
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too. If you want to define an environment variable locally, you should use
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<path>~/.bashrc</path> or <path>~/.bash_profile</path>:
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</p>
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<pre caption="Extending PATH for local usage in ~/.bashrc">
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<comment>(A colon followed by no directory is treated as the current working directory)</comment>
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PATH="${PATH}:/home/my_user/bin:"
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</pre>
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<p>
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When you relogin, your <c>PATH</c> variable will be updated.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>Session Specific</title>
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<body>
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<p>
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Sometimes even stricter definitions are requested. You might want to be able to
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use binaries from a temporary directory you created without using the path to
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the binaries themselves or editing <path>~/.bashrc</path> for the short time
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you need it.
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</p>
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<p>
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In this case, you can just define the <c>PATH</c> variable in your current
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session by using the <c>export</c> command. As long as you don't log out, the
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<c>PATH</c> variable will be using the temporary settings.
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</p>
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<pre caption="Defining a session-specific environment variable">
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# <i>export PATH="${PATH}:/home/my_user/tmp/usr/bin"</i>
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</pre>
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</body>
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</subsection>
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</section>
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</sections>
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