How do I change a folder icon from a script?

[Perl Whore <whoreperl gmail com>]

In nautilus, I can go into properties and change the icon of a folder
to a custom one. Can the same be done from the commandline or is it
possible with DBus? If so, how?

I want to use it in a script.

Also how do I check if it has an icon set already?

Thanks