CODEWITHSUNDEEP
chef-infra
Cory Ringdahl
Cory Ringdahl

Reputation: 542

chef only_if AND not_if in same resource

I'm confused about the logic order of only_if and not_if in Chef's resource model.

In the following example, assuming a file called /tmp/foo containing the word bar:

execute "rm /tmp/foo" do
    action :run
    only_if "ls /tmp/foo"
    not_if "grep bar /tmp/foo"
end

What happens? Are only_if and not_if exclusive? AND? OR? Which comes first? Why?

Upvotes: 3

Views: 6607

Answers (3)

Jason Crease
Jason Crease

Reputation: 1985

As an explicit, generalized statement: "In order to run, all only_ifs must be true, and all not_ifs must be false."

As an example, consider this code:

node.force_default['A'] = true
node.force_default['B'] = true
node.force_default['C'] = false
node.force_default['D'] = false

log 'message' do
  message 'This has run'
  level :error
  only_if { node['A'] }
  only_if { node['B'] }
  not_if { node['C'] }
  not_if { node['D'] }
end

It will print 'This has run'. However, if any of A, B, C or D change, then it will be skipped.

Upvotes: 0

Saravanan G
Saravanan G

Reputation: 581

In general programming terms, "only_if" is similar to "if" and "not_if" is similar to unless (or if !)

So it is always recommended to have either one of the gaurd check in your resource.

For example:

Below code will be creating the user "adam", if the user does not exists:

not_if 'grep adam /etc/passwd', :user => 'adam'

Below code will be creating foo.txt, only if the directory "/tmp" is exists:

file '/tmp/foo.txt' do
  action :create
  only_if { ::Dir.exist?("/tmp") }
end

Also please refer the Chef documentation for "Gaurds" to get further clarity.

Upvotes: 0

coderanger
coderanger

Reputation: 54267

The are run in the order given in the code. The internals of each method basically boils down to @guards << Guard.new(*args) so they track order implicitly. Both clauses must "pass" for the action the run. In general this is a bad idea as it is super hard to read, if you must then leave a very very good comment.

Upvotes: 9

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