knife axe prints diff of objects (environment,data_bag,role) before uploading them.
$ gem install knife-axe
or
$ cp axe*.rb ~/.chef/plugins/knife
$ knife axe role ~/chef-repo/role/role42.rb
$ knife axe env ~/chef-repo/environments/environment42.rb
$ knife axe data bag databagname ~/chef-repo/data_bags/databagname/item42.rb