Sun Studio 12: Fortran User's Guide

3.4.100 –U

Recognize upper and lower case in source files.

Do not treat uppercase letters as equivalent to lowercase. The default is to treat uppercase as lowercase except within character–string constants. With this option, the compiler treats Delta, DELTA, and delta as different symbols. Calls to intrinsic functions are not affected by this option.

Portability and mixing Fortran with other languages may require use of -U. See the Fortran Programming Guide chapter on porting programs to Fortran 95.