Learning Unix for Mac OS X, Second Edition

Customizing Your Shell Environment

The Unix shell reads a number of configuration files when it starts up. These configuration files are really shell programs , so they are extraordinarily powerful. Shell programming is beyond the scope of this book. For more detail, see Paul DuBois’ book Using csh and tcsh (O’Reilly). Because Unix is a multiuser system, there are two possible locations for the configuration files: one applies to all users of the system and another to each individual user.

The system-wide setup files that are read by tcsh , the default shell for Mac OS X, are found in /etc (csh.login, csh.cshrc, and csh.logout). You only have permission to change these system-wide files if you use sudo (see Section 2.3). However, you can create an additional file called .tcshrc in your home directory that will add additional commands to be executed whenever you start a new Terminal window. (If you configure Terminal to use another shell, such as the Bourne shell, the C shell, or the Z shell, you’ll need to set up different configuration files, which we don’t discuss.) The system-wide setup files are read first, then the user-specific ones, so commands in your .tcshrc file may override those in the system-wide files.

The .tcshrc file can contain any shell command that you want to run automatically whenever you create a new Terminal. Some typical examples include changing the shell prompt, setting environment variables (values that control the operation of other Unix utilities), ...