Chef: How to set EDITOR for knife

When I run below command I get the error mentioned below:

$ knife node edit hostname.domain.com
ERROR: You must set your EDITOR environment variable or configure your editor via knife.rb

I wanted to set editor value in the knife.rb but I am not able to find which option would correspond to the editor. I have gone through below links which explain various options supported by knife.rb:

http://docs.opscode.com/config_rb_knife.html

http://docs.opscode.com/config_rb_knife_optional_settings.html

I know I did not overlook above links but i can;'t find an option which is relevant to setting editor value.

Could you point me to the correct options whihc will help me set editor for knife.

Thanks.