"SHELL The full pathname to the shell is kept in this environment variable. If it is not set when the shell starts, Bash assigns to it the full pathname of the current user's login shell."
SHELL is not being exported to the environment on Cygwin. For reference: http://cygwin.com/ml/cygwin/2008-07/msg00280.html $ echo $BASH_VERSION 3.2.39(19)-release
