nginx config question, rules?

This works:
add_header Set-Cookie "EXAMPLE=$SHAIP;Path=/";

This does not work:
if ($http_cookie ~ "EXAMPLE=$SHAIP") {

Why this? How can I get it to work? I want $SHAIP to be checked if exist, basically it will store the cookie if its not set already.

This is what shaip is:
set_sha1 $SHAIP test;

i want it to compare the sha1'd "test" text, if the cookie is set or not.. for some reason i cant put that variable there?

it's a little hard to explain.

if ($http_cookie ~ "EXAMPLE=$SHAIP") {
return 403;
}

How will i do this correctly? basically check if the sha1'd cookie is set.. currently it just checks if that variable is set, instead of the sha1 its elf.