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Global or Environment Variables

A global variable is one that is visible to all shells. It is said to be global because it is not restricted to use by the current shell. To set a global variable in the C shell, the setenv command must be used. This command is used precisely the same as the set command with the exception that it is used for setting global variables (often referred to as environment variables). To see a listing of the current global variables in use, the setenv command can be used without any arguments. To remove a global variable from use, the unsetenv command can be used in the same manner that the unset command was used. The C shell comes with a number of predefined environmental variables which can be read and altered by the user. The lower case variables displayed in the set example are a few of these. Predefined variables are generally lower case which is why it is a good idea to use all upper case when a user defines his own variables (global or otherwise). Some predefined variables are set by the shell during login while others need to be set by the user if he so desires. Table 4.3 contains the predefined environmental variables for the C shell as well a description and default setting

Table 4.3:  Predefined environmental variables and their default setting.

Not all of these variables would be given an explicit value when activated. Some of these variables are either set or unset. The nobeep variable, for example, would be set by simply entering setenv nobeep. If the user wished to have any of these variables set during each session, the variable assignments could be placed into one of the login scripts.

Douglas M Gingrich
Mon Apr 27 15:25:49 MDT 1998