Web domain - 58 Part I . Linux First Steps To
58 Part I . Linux First Steps To set an environment variable temporarily, you can simply type a variable name and assign it to a value. Here s an example: $ AB=/usr/dog/contagious/ringbearer/grind ; export AB This example causes a long directory path to be assigned to the AB variable. The export AB command says to export the value to the shell so that it can be propagated to other shells you may open. With AB set, you go to the directory by typing the following: $ cd $AB The problem with setting environment variables in this way is that as soon as you exit the shell in which you set the variable, the setting is lost. To set variables permanently, add variable settings to a bash configuration file, as described later in this section. If you want to have other text right up against the output from an environment variable, you can surround the variable in braces. This protects the variable name from being misunderstood. For example, if you want to add a command name to the AB variable shown earlier, you can type the following: $ echo ${AB}/adventure /usr/dog/contagious/ringbearer/grind/adventure Remember that you must export the variable so that it can be picked up by other shell commands. You must add the export line to a shell configuration file for it to take effect the next time you log in. The export command is fairly flexible. Instead of running the export command after you set the variable, you can do it all in one step, as follows: $ export XYZ=/home/xyz/bin You can override the value of any environment variable. This can be temporary, by simply typing the new value, or you can add the new export line to your $HOME/.bashrc file. One useful variable to update is PATH: $ export PATH=$PATH:/home/xyz/bin In this example, the /home/xyz/bin directory is added to the PATH, a useful technique if you want to run a bunch of commands from a directory that is not normally in your PATH, without typing the full or relative path each time. If you decide that you no longer want a variable to be set, you can use the unset command to erase its value. For example, you can type unset XYZ, which causes XYZ to have no value set. (Remember to remove the export from the $HOME/.bashrc file if you added it there or it will return the next time you open a shell.)
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