If you only want the file size, you want to check the header of the reply that the server sends to you. The LWP::Simple module has a very convenient method, unimaginatively called head, which does Just That:

use strict;
use LWP::Simple;
my $url = 'http://xxxxx.xxx/xxxxxx/xxxxx/xxxx.gif';
printf "$url : %s bytes", ((head $url)[1]);
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