Keys and Values from Hashes in Ruby Templates

Reference: http://ruby-doc.org/stdlib-1.9.3/libdoc/erb/rdoc/ERB.html
ERB recognizes certain tags in the provided template and converts them based on the rules below:

<% Ruby code -- inline with output %>
<%= Ruby expression -- replace with result %>
<%# comment -- ignored -- useful in testing %>
% a line of Ruby code -- treated as <% line %> (optional -- see ERB.new)
%% replaced with % if first thing on a line and % processing is used
<%% or %%> -- replace with <% or %> respectively

Create a new “motd” cookbook

$ knife cookbook create motd

Example: ~/cookbooks/motd/recipes/default.rb

#
# Cookbook Name:: motd
# Recipe:: default
#
# Copyright 2012, YOUR_COMPANY_NAME
#
# All rights reserved - Do Not Redistribute
#

template "/home/motd" do
  source "motd.erb"
  owner "root"
end

Example: ~/cookbooks/motd/template/default/motd.erb
* You can find out what hashes are defined on a system by running “ohai”

Hostname : <%= node["hostname"] %>
Platform : <%= node["platform"] %>

Memory Usage
<% node["memory"].each_pair do |k,v| %>
<%= k %>     : <%= v%>
<% end %>

Block Devices
<% node["block_device"].each_pair do |k,v| %>
Key: <%= k %>   -   <%= v%>
<% end %>

Network Info
<% node["network"]["interfaces"].keys.each do |k| %>
Key: <%= k %>
<% end %>

<% node["network"]["interfaces"].values.each do |v| %>
Value: <%= v %>
<% end %>

Run chef-client with the “motd” cookbook installed and look at the output at

$ cat /home/motd

Hostname: ubuntu01
Platform: ubuntu

Memory Usage
vmalloc_total     : 34359738367kB
anon_pages     : 129892kB
writeback     : 0kB
dirty     : 0kB
vmalloc_used     : 266104kB
vmalloc_chunk     : 34359469948kB
active     : 186264kB
buffers     : 31252kB
commit_limit     : 773540kB
nfs_unstable     : 0kB
slab_unreclaim     : 11684kB
bounce     : 0kB
slab_reclaimable     : 17644kB
mapped     : 11580kB
cached     : 190268kB
slab     : 29328kB
inactive     : 165136kB
free     : 105708kB
total     : 502612kB
committed_as     : 926460kB
page_tables     : 4324kB
swap     : cached0kBfree522236kBtotal522236kB

Block Devices
Key: sda   -   timeout30modelVMware Virtual Sremovable0vendorVMware,rev1.0size41943040staterunning
Key: sr0   -   timeout30modelVMware IDE CDR10removable1vendorNECVMWarrev1.00size1401432staterunning
Key: fd0   -   removable1size0
Key: loop7   -   removable0size0
Key: loop6   -   removable0size0
Key: loop5   -   removable0size0
Key: loop4   -   removable0size0
Key: loop3   -   removable0size0
Key: loop2   -   removable0size0
Key: loop1   -   removable0size0
Key: loop0   -   removable0size0
Key: ram15   -   removable0size131072
Key: ram14   -   removable0size131072
Key: ram13   -   removable0size131072
Key: ram12   -   removable0size131072
Key: ram11   -   removable0size131072
Key: ram10   -   removable0size131072
Key: ram9   -   removable0size131072
Key: ram8   -   removable0size131072
Key: ram7   -   removable0size131072
Key: ram6   -   removable0size131072
Key: ram5   -   removable0size131072
Key: ram4   -   removable0size131072
Key: ram3   -   removable0size131072
Key: ram2   -   removable0size131072
Key: ram1   -   removable0size131072
Key: ram0   -   removable0size131072

Network Info
Key: eth0
Key: lo

Value: mtu16436encapsulationLoopbackflagsLOOPBACKUPLOWER_U....< i truncated output >
Value: mtu1500typeethencapsulationEthernetflagsBROADCASTM....< i truncated output >

Also for shits and giggles
Example Ohai output:

root@ubuntu01:~# ohai

{
  "idletime": "35 minutes 35 seconds",
  "uptime": "36 minutes 47 seconds",
  "dmi": {
    "base_board": {
      "chassis_handle": "0x0000",
      "location_in_chassis": "Not Specified",
      "product_name": "440BX Desktop Reference Platform",
      "serial_number": "None",
      "manufacturer": "Intel Corporation",
      "version": "None",
      "type": "Unknown",
      "features": "None",
      "contained_object_handles": "0",
      "all_records": [
  .. < i truncated output >