/sys$common/syshlp/helplib.hlb Lexicals, F$DIRECTORY, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  $ SAVE_DIR = F$DIRECTORY()
  $ SET DEFAULT [CARLEN.TESTFILES]
     .
     .
     .
  $ SET DEFAULT 'SAVE_DIR'

      This example shows an excerpt from a command procedure that
      uses the F$DIRECTORY function to save the current default
      directory setting. The assignment statement equates the symbol
      SAVE_DIR to the current directory. Then the SET DEFAULT command
      establishes a new default directory. Later, the symbol SAVE_DIR
      is used in the SET DEFAULT command that restores the original
      default directory.

      Note that you can use the F$ENVIRONMENT function with the
      DEFAULT keyword to return the default disk and directory.
      You should use the F$ENVIRONMENT function rather than the
      F$DIRECTORY function in situations involving more than one
      disk.