[how to obtain the identification or name of an object, from the script of another object]

Hello community! ,
I have an object-circle with an id and name, and another as a square, what I am doing is converting the square as a 
button so that when I touch it the other objetc-circle is positioned in some area,

I need to get the id of the circle object from the square object script.
if someone has a code snippet, it would help me a lot
thanks