Decaying exponential function plot

I want to plot an exponential function that approaches 1, then decays to zero. I have tried the script below. The function approaches 1 but does not decay. What have I done wrong?

Many Thanks! JMT

t = 0:0.1:10;
y = 1 - exp(-t);
if t>5
y = exp(-t);
end;
plot (t,y)