Some common logical names with default extensions are:
HKLIN input MTZ reflection file (.mtz);
HKLOUT output MTZ reflection file (.mtz);
MAPIN input map file (.map);
MAPOUT output map file (.map);
XYZIN input coordinate file (.brk);
XYZOUT output coordinate file (.brk).
In some cases more than one file corresponding to the same type of entry in `$CINCL/default.def is required e.g., several input reflexion files. In this case they are typically specified as HKLINn, for instance, where n is a sequence number. The rules for matching logical names with the default specifications given above then apply to the prefix of the name which matches the entries in the files `$CINCL/environ.def and `$CINCL/default.def.
In Unix the environment variable CCP4_OPEN can be used to determine whether logical names opened as new over-write existing files with the name specified. Over-writing will occur if the value of the variable is UNKNOWN; otherwise the program will abort. Setting the equivalent symbol in VMS is less useful because of the file version mechanism.