DefaultDir$
A string variable that contains the default directory for the running Just BASIC program.  The format is "drive:\dir1", or "drive:\dir1\dir2" etc.  There is no backslash appended to the DefaultDir$ variable.  

Usage:
    print DefaultDir$

As used with a FILES statement:
    files DefaultDir$, "*.txt", info$(

As used to access a text file in the same directory as the program.  Notice that the backslash must be added to the beginning of the filename:
    open DefaultDir$ + "\readme.txt" for append as #f
    print #f, "Sample"
    close #f