5.7 Files opened without an explicit ACTION= specifier

The Fortran standard says that if an OPEN statement is executed without an explicit ACTION= specifier, the default value is processor dependent. GNU Fortran behaves as follows:

1. Attempt to open the file with ACTION='READWRITE'
2. If that fails, try to open with ACTION='READ'
3. If that fails, try to open with ACTION='WRITE'
4. If that fails, generate an error