This does not work with the patterns of the operating system.
Use a regexp call to filter the names instead:
List = dir('*.txt'):
Name = {List.Name};
% Name = {'1234.txt', '1234s.txt', '1265', 'a1234.txt'};
matchC = regexp(Name, '^\d+\.txt', 'start') % Or: '^[0-9]+\.txt'
match = ~cellfun('isempty', matchC)
List = List(match);
