Set

Usage: set [variable [value]]

Used by itself, set lists all environment variables which have been set.

With just a variable name as an argument, set will set the value of that environment variable to "".

If given a second argument, a value, a variable is created with that name and that value if it doesn't exist. If it already exists, the old value is replaced with the new one.

Some of the possible environment variables are:
LINES - set the number of lines on your screen (default 24).
TZONE - your timezone (one of EST, CST, MST, PST, BST, GMT, CET, EET, AST). Lets the game display all times in your time zone's units.
mail_notification - inform you when you receive some mail. (0/1)