Accessing Ruby Hash value using a string

Question

I have a ruby array like below

tomcats = [
  'sandbox',
  'sandbox_acserver',
  'sandbox_vgw'
]

I need to pass the string as a hash index like below

tomcats.each do |tomcat_name|
  obi_tomcat '#{tomcat_name}' do
    Chef::Log::info("Creating tomcat instance - #{tomcat_name}")
    Chef::Log::info("#{node['obi']['tomcat']['sandbox'][:name]}") // works
    Chef::Log::info("#{node['obi']['tomcat']['#{tomcat_name}'][:name]}") // doesn't work
  end
end

The last log throws an error since the access with #{tomcat_name} is nil. I'm new to ruby. How do I access with key as the tomcat_name ?

Amadan · Accepted Answer · 2014-08-08 04:48:30Z

3

In normal code, you'd write:

node['obi']['tomcat'][tomcat_name][:name]

In a string interpolation (useless here, because it's the only thing in the string in this case), it is completely the same:

"#{node['obi']['tomcat'][tomcat_name][:name]}"

answered Aug 8, 2014 at 4:48

Amadan

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3 Comments

vee Over a year ago

So basically, calling Chef::Log::info(node['obi']['tomcat'][tomcat_name][:name]) should work!

Amadan Over a year ago

Yup. You only need interpolation if you want to insert stuff in a bigger string, like in your first info line - "#{foo}" is same as foo, but "Big #{foo}!" is same as "Big " + foo + "!", which is not as readable.

Wenbing Li Over a year ago

This one may be more useless in this case, but it still work: "#{node['obi']['tomcat']["#{tomcat_name}"][:name]}"

user1375096 · Accepted Answer · 2014-08-08 04:49:43Z

2

#{} only works in double quote, as "#{tomcat_name}".

But you don't need the syntax here, just use [tomcat_name] directly.

answered Aug 8, 2014 at 4:49

user1375096

Comments

Wenbing Li · Accepted Answer · 2014-08-08 05:38:48Z

When I saw this question, I'm thinking whether ruby placeholder could be put inside other placeholder in string interpolation. And I found that ruby actually support it, and most interesting thing is that you don't need to escape the " inside the string.

Although it is not very useful in this case, it still works if you write as below:

Chef::Log::info("#{node['obi']['tomcat']["#{tomcat_name}"][:name]}")

Below is an simple example of placeholder inside other placeholder:

tomcats = [
  'sandbox',
  'sandbox_acserver',
  'sandbox_vgw'
]

node = {
    'sandbox_name' => "sandbox name",
    'sandbox_acserver_name' => "sandbox_acserver name",
    'sandbox_vgw_name' => "sandbox_vgw name",
}

tomcats.each do | tomcat |
    puts "This is tomcat : #{node["#{tomcat}_name"]}"
end

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