The operating system commands SET, CD, and <drive>: can also be used in !IF expressions. Specifying these commands within !IF statements will guarantee that they are executed before any compile is processed at read-time.
The syntax for this type of !if expression is:
!if [command]
where the commands set, cd, and <drive>: are enclosed in square brackets.
Example:
The following line in a description file:
!if [cd \] == 0
will change the directory to the root directory and execute the statement(s) after the !if, if the return code from the command is 0.