[PLUG] what is the meaning of '~~' in a shell script?

[Galen Seitz]

I'm looking at the hotplug rules on an OpenWRT router.  Here's a excerpt.

SUBSYSTEM ~~ 
(^net$|^input$|^button$|^usb$|^ieee1394$|^block$|^atm$|^zaptel$|^tty$) {
	exec /sbin/hotplug-call %SUBSYSTEM%
}


What is the meaning of the '~~'?

How could I have found the answer myself with a search?  (i.e. is there 
a way to search for ~~)

thanks,
galen
-- 
Galen Seitz
galens at seitzassoc.com