$|=1;

print <<"EoF";
Content-type: multipart/x-mixed-replace; boundary=1234

--1234
Content-type: text/html

<h1>Test 123...</h1>

--1234
EoF

sleep 2;

print <<"EoF";
Content-type: text/html

<h1>Test 456...</h1>

--1234
EoF