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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/1.0 --> |
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<!-- $Header: /home/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-variables.xml,v 1.3 2003/12/16 18:37:29 swift Exp $ --> |
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<sections> |
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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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|
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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 a |
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bit weird or unmanageable. This is however wrong: by using environment variables |
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one can easily change a configuration setting for one or more applications. |
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</p> |
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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<pre caption="/etc/conf.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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|
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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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|
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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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|
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<p> |
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This doesn't only benefit 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 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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|
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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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|
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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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|
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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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|
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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 wrong: 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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|
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<p> |
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The <c>env-update</c> script will append the values in the alphabetical order of |
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the <path>/etc/env.d</path> files. This is why many of the files in |
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<path>/etc/env.d</path> begin with a number. |
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</p> |
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|
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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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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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|
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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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|
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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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|
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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> 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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|
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<pre caption="Extending PATH for local usage in ~/.bashrc"> |
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PATH="${PATH}:/home/my_user/bin" |
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</pre> |
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|
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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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|
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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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|
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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 those few moments |
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you need it. |
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</p> |
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|
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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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|
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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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|
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</body> |
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</subsection> |
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</section> |
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</sections> |
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