Description files can use a special syntax to determine the drive, path, base name, and extension of the first dependent file in a description block. This syntax is called the extmake syntax.
The characters %s represent the complete file specification of the first dependent file. Various parts of the file specification are represented using the following syntax:
%<parts>
For example, to specify the drive and path name of the first dependent file in a description block, use:
%<dp>
The percent symbol (%) is a replacement in DOS and Windows command lines. To use the percent symbol in command-line arguments, use a double percent (%%).