Handbuch:IA64/Arbeiten/Umgebungsvariablen
Umgebungsvariablen
Einleitung
Eine Umgebungsvariable ist ein benanntes Objekt, das Informationen enthält, die von einer oder mehreren Anwendungen verwendet werden. Durch die Verwendung von Umgebungsvariablen kann man auf einfache Weise eine Konfigurationseinstellung für eine oder mehrere Anwendungen ändern.
Wichtige Beispiele
Die folgende Tabelle enthält eine Reihe von Variablen, die von einem Linux-System verwendet werden, und beschreibt ihre Verwendung. Im Anschluss an die Tabelle sind Beispielwerte aufgeführt.
| Variable | Description |
|---|---|
| PATH | This variable contains a colon-separated list of directories in which the system looks for executable files. If a name is entered of an executable (such as ls, rc-update, or emerge) but this executable is not located in a listed directory, then the system will not execute it (unless the full path is entered as the command, such as /bin/ls). |
| ROOTPATH | This variable has the same function as PATH, but this one only lists the directories that should be checked when the root-user enters a command. |
| LDPATH | This variable contains a colon-separated list of directories in which the dynamical linker searches through to find a library. |
| MANPATH | This variable contains a colon-separated list of directories in which the man command searches for the man pages. |
| INFODIR | This variable contains a colon-separated list of directories in which the info command searches for the info pages. |
| PAGER | This variable contains the path to the program used to list the contents of files through (such as less or more). |
| EDITOR | This variable contains the path to the program used to change the contents of files with (such as nano or vi). |
| KDEDIRS | This variable contains a colon-separated list of directories which contain KDE-specific material. |
| CONFIG_PROTECT | This variable contains a space-delimited list of directories which should be protected by Portage during updates. |
| CONFIG_PROTECT_MASK | This variable contains a space-delimited list of directories which should not be protected by Portage during updates. |
Nachstehend finden Sie ein Beispiel für die Definition all dieser Variablen:
PATH="/bin:/usr/bin:/usr/local/bin:/opt/bin:/usr/games/bin" ROOTPATH="/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin" LDPATH="/lib:/usr/lib:/usr/local/lib:/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3" MANPATH="/usr/share/man:/usr/local/share/man" INFODIR="/usr/share/info:/usr/local/share/info" PAGER="/usr/bin/less" EDITOR="/usr/bin/vim" KDEDIRS="/usr" CONFIG_PROTECT="/usr/X11R6/lib/X11/xkb /opt/tomcat/conf \ /usr/kde/3.1/share/config /usr/share/texmf/tex/generic/config/ \ /usr/share/texmf/tex/platex/config/ /usr/share/config" CONFIG_PROTECT_MASK="/etc/gconf"
Globale Definition von Variablen
Das env.d-Verzeichnis
Um die Definition dieser Variablen zu zentralisieren, hat Gentoo das Verzeichnis /etc/env.d/ eingeführt. Innerhalb dieses Verzeichnisses gibt es eine Reihe von Dateien, wie z.B. 00basic, 05gcc, usw., die die Variablen enthalten, die von der im Namen genannten Anwendung benötigt werden.
Wenn z.B. gcc installiert wird, wurde eine Datei namens 05gcc vom Ebuild erstellt, die die Definition der folgenden Variablen enthält:
/etc/env.d/05gccDefault gcc enabled environment variablesPATH="/usr/i686-pc-linux-gnu/gcc-bin/3.2" ROOTPATH="/usr/i686-pc-linux-gnu/gcc-bin/3.2" MANPATH="/usr/share/gcc-data/i686-pc-linux-gnu/3.2/man" INFOPATH="/usr/share/gcc-data/i686-pc-linux-gnu/3.2/info" CC="gcc" CXX="g++" LDPATH="/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3"
Other distributions might tell their users to change or add such environment variable definitions in /etc/profile or other locations. Gentoo on the other hand makes it easy for the user (and for Portage) to maintain and manage the environment variables without having to pay attention to the numerous files that can contain environment variables.
For instance, when gcc is updated, the /etc/env.d/05gcc file is updated too without requesting any user-interaction.
This not only benefits Portage, but also the user. Occasionally users might be asked to set a certain environment variable system-wide. As an example we take the http_proxy variable. Instead of messing about with /etc/profile, users can now just create a file (say /etc/env.d/99local) and enter the definition(s) in it:
/etc/env.d/99localSetting a global variablehttp_proxy="proxy.server.com:8080"
By using the same file for all self-managed variables, users have a quick overview on the variables they have defined themselves.
env-update
Several files in /etc/env.d/ define the PATH variable. This is not a mistake: when the env-update command is executed, it will append the several definitions before it updates the environment variables, thereby making it easy for packages (or users) to add their own environment variable settings without interfering with the already existing values.
The env-update script will append the values in the alphabetical order of the /etc/env.d/ files. The file names must begin with two decimal digits.
00basic 99kde-env 99local
+-------------+----------------+-------------+
PATH="/bin:/usr/bin:/usr/kde/3.2/bin:/usr/local/bin"The concatenation of variables does not always happen, only with the following variables: ADA_INCLUDE_PATH, ADA_OBJECTS_PATH, CLASSPATH, KDEDIRS, PATH, LDPATH, MANPATH, INFODIR, INFOPATH, ROOTPATH, CONFIG_PROTECT, CONFIG_PROTECT_MASK, PRELINK_PATH, PRELINK_PATH_MASK, PKG_CONFIG_PATH, and PYTHONPATH. For all other variables the latest defined value (in alphabetical order of the files in /etc/env.d/) is used.
It is possible to add more variables into this list of concatenate-variables by adding the variable name to either COLON_SEPARATED or SPACE_SEPARATED variables (also inside an /etc/env.d/ file).
When executing env-update, the script will create all environment variables and place them in /etc/profile.env (which is used by /etc/profile). It will also extract the information from the LDPATH variable and use that to create /etc/ld.so.conf. After this, it will run ldconfig to recreate the /etc/ld.so.cache file used by the dynamical linker.
To notice the effect of env-update immediately after running it, execute the following command to update the environment. Users who have installed Gentoo themselves will probably remember this from the installation instructions:
root #env-update && source /etc/profileThe above command only updates the variables in the current terminal, new consoles, and their children. Thus, if the user is working in X11, he needs to either type source /etc/profile in every new terminal opened or restart X so that all new terminals source the new variables. If a login manager is used, it is necessary to become root and restart the /etc/init.d/xdm service.
It is not possible to use shell variables when defining other variables. This means things like
FOO="$BAR" (where $BAR is another variable) are forbidden.Defining variables locally
User specific
It might not be necessary to define an environment variable globally. For instance, one might want to add /home/my_user/bin and the current working directory (the directory the user is in) to the PATH variable but do not want all other users on the system to have that in their PATH too. To define an environment variable locally, use ~/.bashrc or ~/.bash_profile:
~/.bashrcExtending PATH for local usage# A colon followed by no directory is treated as the current working directory PATH="${PATH}:/home/my_user/bin:"
After logout/login, the PATH variable will be updated.
Session specific
Sometimes even stricter definitions are requested. For instance, a user might want to be able to use binaries from a temporary directory created without using the path to the binaries themselves or editing ~/.bashrc for the short time necessary.
In this case, just define the PATH variable in the current session by using the export command. As long as the user does not log out, the PATH variable will be using the temporary settings.
root #export PATH="${PATH}:/home/my_user/tmp/usr/bin"