Equivalent of String.Format in a Chef/Bash Recipe - linux

Question

looking for something similar to .Net string format in a chef recipe ie.
string phone = String.format("phone: {0}",_phone);
I have a Chef recipe where I need to build up a command string with 30 of these params so hoping for a tidy way to build the string, in principle Im doing this
a=node['some_var'].to_s
ruby_block "run command" do
block do
cmd = shell_out!("node mycommand.js #{a}; exit 2;")
end
end
When I try this I get the error
Arguments to path.join must be strings any tips appreciated

Answer 1

Chef runs in two phases:
Compile and Execute (see https://www.chef.io/blog/2013/09/04/demystifying-common-idioms-in-chef-recipes/ for more details).
Your variable assignment to a happens at compile time, e.g. when chef loads all recipes. The ruby block will be execute in execution mode at converge time and cannot access the variable a.
So the easiest solution might be putting the attribute into the ruby block:
ruby_block "run command with argument #{node['some_var']}" do
block do
shell_out!("node mycommand.js #{node['some_var']}")
end
end
However:
If you don't need to execute Ruby code, consider using the execute or bash resource instead.
Keep in mind, that you must have a unique resource name, if you're building some kind of loop around it. An easy way is to put something unique into the name ruby_block "something unique per loop iteration" do ... end
What I really don't understand is your exit code 2. This is an error code. It will make chef throw an exception each time. (shell_out! throws an exception if exit code != 0, see https://github.com/chef/chef/blob/master/lib/chef/mixin/shell_out.rb#L24-L28)
The resource will be executed on each chef run. This is probably not in your interest. Consider adding a guard (test), to prevent unnecessary execution, see https://docs.chef.io/resource_common.html#guards