How to detect bash?

[mwoehlke]

Anyone have any clever, VERY reliable tricks for detecting if the 
current shell is bash? The obvious way is '[ -n "$BASH" ]', but in the 
interest of catching idiots that set BASH to get around such a check, I 
came up with:

[ "`BASH_SUBSHELL=975 ; ( echo $BASH_SUBSHELL )`" -eq 976 ]

(975 is of course an arbitrary number.)

Anyone think they know a better way (or a reason the above might not 
work)? I'm guessing it can still be circumvented*, but one would have to 
be specifically making an effort to do so.

(* Actually, I'm not 100% certain it can; you have to be able to run a 
script upon sub-shell startup. I'm assuming that can be done, but maybe 
I'm wrong...)

--
Matthew
KDE: Desktop Excellence