Hi Dan
> what command do I use to substitute all occurences of a certain string (say,
> "NOT NULL") with another arbitrary string, (e.g. "")? I've tried grep and
> tr, but can't figure it out.
if substitution in 'vi' is not possible due to the size of the file try the
stream editor 'sed'
e.g.:
sed /"NOT NULL"/s/"NOT NULL"/""/ filename > filename2
(I am not sure, if ... filename > filename is appropriate)
Jochen