At login the C (and TC shell) reads initialisation files in your home directory . First it reads the file .cshrc ( .tcshrc for TC shell) followed by the file .login . In addition to environmental variables, both these shells have a number of local shell variables which are not exported to the environment. When another shell is created to run a program, it only reads the .cshrc ( .tcshrc ) file, but it inherits any environment variables that were set up at login. more .. ...