Using $ in quotes with characters after it

[Dan]

Hello,

I've noticed something strange when using grep.  It has to do with a
pattern similar to this one: "hello$world".  It seems to me that the
command executes fine, but the output does not seem to be in any way
predictable.  Of course the $ token signals the end of a line, so this
doesn't really make sense as a regular expression, but why does grep output
anything at all?  It should really throw an error when receiving
expressions like that one.  One other thing, having the pattern in quotes
matters.  If you don't quote it then grep outputs nothing, which is still
not what I would expect but at least the malformed regexp isn't throwing
false matches.  If there's a reason for this behavior could somebody please
enlighten me on why and what the logic is when dealing with the bad pattern?

Thanks,
Daniel Wilson
-- 
~~ Whatever happens, the sun's still gonna come up tomorrow ~~