Edit( filename )
Edit starts an editor  with  the file  whose  filename is given by  the
string filename, and reads the file back into  GAP when you exit the
editor again.  You should set the GAP variable EDITOR to the name of
the  editor  that you  usually use,  e.g.,  /usr/ucb/vi.   This can for
example  be done in   your .gaprc file  (see  the sections on operating
system dependent features in chapter Getting and Installing GAP).
GAP 3.4.4