I guess most personal routers do not ship with bash. This is what mine says:

# ls -l /bin/*sh

lrwxrwxrwx 1 root root 12 Feb 9 2014 /bin/ash -> /bin/busybox

lrwxrwxrwx 1 root root 12 Feb 9 2014 /bin/sh -> /bin/busybox