DouKaku?

%% Terminal 1
%   stty raw < /dev/tty
%   gs -sDEVICE=nullpage echoback.ps 

%% Terminal 2
%   gs -sDEVICE=nullpage pause.ps 

%------------------ echoback.ps ----- Cut Here ---------
%!PS

/Stdin (%stdin) (r) file def
(/tmp/test) (w) file closefile

% p: 112, q: 113
{
    Stdin read
    {
        (/tmp/test) (w) file dup 2 index write closefile
        113 eq { exit } if
    } {exit} ifelse
} loop
quit



%--------------------  pause.ps ------  Cut Here  ---------
%!PS

/Sleep { % OutputFlag Timer  Sleep   OutputFlag'
    realtime
    {
        realtime 1 index sub
        2 index ge {exit} if
        (/tmp/test) (r) file dup read 
        {
            exch closefile (/tmp/test) (w) file exch
            dup 113 eq { quit } if
            112 eq { 4 -1 roll not 4 1 roll } if
        } if
        closefile
    } loop
    pop
    pop
} def


true 
{
    1000 Sleep
    dup {(a) print flush} if
} loop