From MorphOS Library
Set - Creates or modifies specified local environment variable
NAME - Name of the environment variable STRING - value to attach to the variable
Set with NAME and STRING arguments creates a new environment variable. The first word after Set is taken as the NAME. Everything else on the command line is taken as the STRING argument. Quotation marks are not required.
An environment variable created with Set is local to the Shell in which it was created. If you create a new Shell with the NEWSHELL command, that Shell also recognizes any variables created in its parent Shell. However, if you create a new Shell with the Execute Command Ambient menu item or by opening the Shell icon, variables created with SET are not recognized in the new Shells.
NOTE: Set with no arguments lists the current local variables.