How can I concatenate two strings together?

%% string1 string2 append string
% Function: Concatenates two strings together.
/append {
         2 copy length exch length add  % find the length of the new.
         string dup     % string1 string2 string string
         4 2 roll       % string string string1 string2
         2 index 0 3 index
         % string string string1 string2 string 0 string1
         putinterval    % stuff the first string in.
         % string string string1 string2
         exch length exch putinterval
} bind def