In bash you test like this for problems that can be caused by non-printable characters since if you don't know how to identify it because it basically breaks your script.
echo "url=$url" should print something like this normally if you have properly formatted input/text:
But if you have some weird hidden characters (not visible in a text editor of any sort you'll get something like this
This error is annoying, in a Virtuozzo KB entry about this ip tables nat problem they say the kernel needs to be ugpraded:
The node runs 2.6.18-x kernel older than 2.6.18-028stab053.10.
NAT module does not work in container, you get "can't initialize iptables table 'nat'" error:
# iptables -t nat........