i want to have a code that runs continously...

i have two movie clips on the stage. clip1 and clip2
i want to have a code that reposition clip2 base on the height of clip1

for ex... i have a shape tween animation in clip1 that expands the height of a rect.

as the rect is expanding, i want clip2 to be repositioned base on the height, so clip2 is always below the bottom of clip1.

can someone please help?