[chef] Get node attributes from environment

[< >]

Hello.
I'm trying get node attribute from environment :
<code>
if node[:platform] == "ubuntu"
  default_attributes "troll" => "70lvl"
end
</code>
but error pops up, then i'm uploading environment file to chef-server:
<code>
$ knife environment from file dev.rb
ERROR: knife encountered an unexpected error
This may be a bug in the 'environment from file' knife command or plugin
Please collect the output of this command with the `-VV` option before filing 
a
bug report.
Exception: NameError: undefined local variable or method `node' for
#<Chef::Environment:0x7f1e8d08f270>

$ knife environment from file dev.rb -VV
DEBUG: Using configuration from /home/sabadash/.chef/knife.rb
/home/sabadash/chef-repo/environments/dev.rb:12:in `from_file': undefined 
local
variable or method `node' for #<Chef::Environment:0x7fd7499b4b50> (NameError)
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife/core/object_loader.rb:96:in
`object_from_file'
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife/core/object_loader.rb:42:in
`load_from'
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife/environment_from_file.rb:59:in
`load_environment'
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife/environment_from_file.rb:77:in
`run'
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife/environment_from_file.rb:76:in
`each'
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife/environment_from_file.rb:76:in
`run'
    from /usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife.rb:408:in
`run_with_pretty_exceptions'
    from /usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/knife.rb:168:in
`run'
    from
/usr/lib/ruby/gems/1.8/gems/chef-10.16.2/lib/chef/application/knife.rb:123:in
`run'
    from /usr/lib/ruby/gems/1.8/gems/chef-10.16.2/bin/knife:25
    from /usr/bin/knife:19:in `load'
    from /usr/bin/knife:19
</code>

Can you please explain to me why is this happening? Is it possible to get node
attributes from environment?