---------- BEGIN /cgi-bin/ip_addr_as_text ----------
#!/bin/sh

cat << __EOI__
Content-Type: text/plain

$REMOTE_ADDR
__EOI__
----------- END /cgi-bin/ip_addr_as_text -----------

---------- BEGIN client code ----------
use LWP::Simple ();
$content = LWP::Simple::get("http://bla/cgi-bin/ip_addr_as_text");
die(...) unless (LWP::Simple::is_success());
chomp($content);
----------- END client code -----------