How to iterate over an array in Puppet

Question

I would like to iterate over an array that is stored as a Facter fact, and for each element of the array create a new system user and a directory, and finally make API calls

Answer 1

As of latest Puppet (6.4.2), and since Puppet 4, iteration over arrays is supported in a few ways:

$my_arr = ['foo', 'bar', 'baz']

Each function:

$my_arr.each |$v| {
  notice($v)
}

Each function alternative syntax:

each($my_arr) |$v| {
  notice($v)
}

To get the index:

Pass a second argument to each:

$my_arr.each |$i, $v| {
  notice("Index: $i, value: $v")
}

Comparison with Ruby:

Note that this grammar is inspired by Ruby but slightly different, and it's useful to show the two side by side to avoid confusion. Ruby would allow:

my_arr.each do |v|
  notice(v)
end

Or:

my_arr.each { |v|
  notice(v)
}

Other iteration functions:

Note that Puppet provides a number of other iteration functions:

• each - Repeats a block of code a number of times, using a collection of values to provide different parameters each time.

• slice - Repeats a block of code a number of times, using groups of values from a collection as parameters.

• filter - Uses a block of code to transform a data structure by removing non-matching elements.

• map - Uses a block of code to transform every value in a data structure.

• reduce - Uses a block of code to create a new value, or data structure, by combining values from a provided data structure.

• with - Evaluates a block of code once, isolating it in its own local scope. It doesn’t iterate, but has a family resemblance to the iteration functions.

Puppet 3 and earlier:

If you have inherited old code still using Puppet 3, the accepted answer is still correct:

define my_type {
  notice($name)
}

my_type { $my_arr: }

Note however that this is usually considered bad style in modern Puppet.

Answer 2

Puppet 3.7 released earlier this month have the new DSL, which one feature is the iteration, check the following URL https://docs.puppetlabs.com/puppet/latest/reference/experiments_lambdas.html#enabling-lambdas-and-iteration

these new features can be enabled with the :

Setting parser = future in your puppet.conf file or adding the command line switch --parser=future

hope that helps

Answer 3

As of puppet 3.2 this is possible using the "future" parser like so:

$my_env = [ 'shared1', 'shared2', 'shared3', ]
each($my_env) |$value| {
  file { "/var/tmp/$value":
    ensure => directory,
    mode => 0600,
  }
  user { $value:
    ensure -> present,
  }
}

See also: http://docs.puppetlabs.com/puppet/3/reference/lang_experimental_3_2.html#background-the-puppet-future-parser

Answer 4

This might work, depending on what you are doing

# Assuming fact my_env => [ shared1, shared2, shared3 ]

define my_resource {
  file { "/var/tmp/$name":
    ensure => directory,
    mode   => '0600',
  }
  user { $name:
    ensure => present,
  }
}
my_resource { $my_env: }

It will work if your requirements are simple, if not, Puppet makes this very hard to do. The Puppet developers have irrational prejudices against iteration based on a misunderstanding about how declarative languages work.

If this kind of resource doesn't work for you, perhaps you could give a better idea of which resource properties you are trying to set from your array?

EDIT:

With Puppet 4, this lamentable flaw was finally fixed. Current state of affairs documented here. As the documentation says, you'll find examples of the above solution in a lot of old code.

Answer 5

There is a "create_resources()" function in puppet. that will be very helpful while iterating over the list of itmes

Answer 6

itsbruce's answer is probably the best for now, but there is an iteration proposal going through puppetlabs' armatures process for possible implementation in future.