you might try
in reply to pulling php into perl
my $online_indicator = 'http://mydomain.com/chatmonk3y/online_indicato
+r/webber.php?jid=' . $seller . '@mydomain.com';
# or more abstract
# my $online_indicator = $protocol . $hostname . $pathToScript . $argu
Note that double quotes force content negotiation whereas single quotes don't (which slightly speeds up the script as some parsing isn't needed).
Have a nice day
All decision is left to your taste
But what does my $scalar($seller) do? Where do you use that?
Might be helpfull to post some more code to better document the context of the problem.