When the macro processor executes a macro program statement that can create a macro variable (such as a %LET statement), the macro processor attempts to change the value of an existing macro variable ...

store values in macro variables (for example, to pass information from the current SCL program to subsequent programs in the application, to subsequent applications, or to other parts of SAS software) ...

These variables can be used in batch files, through the Run utility and in a programming environment such as VB and VBA. Typing % UserProfile% references the current user. Typing % UserProfile%\My ...

Your program will depend on all sorts of facilities ... but it lets you explore the flow of the macro, examine variables, and more. You can read more about it on the GitHub page, but essentially ...