How I draw partial function?

hi, everyone I want to plot partial function like these code:

clear,clc

x1=2:.01:6;

x2=4:.01:8;

y1=(2*(x1+1)-6)+(-2*(x2+1)+14);

y2=(2*(x1-1)-6)+(-2*(x2-1)+14);

x=[x1 x2];

y=[y1 y2];

x_line=0:.01:8;

y_line=0*x_line;

% h is assumed to be 4 and l is assumed to be 8.

figure(1)

plot(x,y,'r',x_line,y_line,'--k','linewidth',2)

axis([0 8 -6 6])

title('Initial Shape of f(x)')

xlabel('length')

ylabel('h')

I can create this

but, i cannot following

thanks a lot

[darova]

what about impoly?