Hi, I'm wondering whether trying to use string substitution with an undefined string variable shouldn't throw an error. Example: gretl version 1.9.9cvs Current session: 2012-09-28 11:20 ? if !isnull(check) ? delete check ? endif ? print "This prints @check" This prints @check I would argue that the unescaped @-sign is a clear indication that the script author wanted to refer to the variable 'check'. Since that doesn't exist, gretl should complain. thanks, sven