Your problem is due to bad programming practices. I recommend to put each instruction in a separate line. If you do that your script works. If you don't do that you have to put a semicolon after each instruction.
w = [0:1:100]*pi/100;
X = exp(j*w) ./ (exp(j*w) - 0.2*ones(1,101));
magX = abs (X);
angX = angle (X);
realX = real(X);
imagX = imag(X);
subplot(2,2,1);
plot(w/pi,magX);
xlabel('frequency in pi units');
title('Magnitude Part');
ylabel('Magnitude')
subplot(2,2,2);
plot(w/pi,angX);
xlabel('frequency in pi units');
title('AnglePart');
ylabel('Radians')
subplot(2,2,3);
plot(w/pi,realX);
xlabel('frequency in pi units');
title('Real Part');
ylabel('Real')
subplot(2,2,4);
plot(w/pi,imagX);
xlabel('frequency in pi units');
title('Imaginary Part');
ylabel('Imaginary')
