Iterating over multiple items

A hash is like an array, but each of the elements can be stored and looked up by name (referred to as the key), for example (hash.pp):

$interface = {
  'name' => 'eth0',
  'ip'   => '192.168.0.1',
  'mac'  => '52:54:00:4a:60:07' 
}
notify { "(${interface['ip']}) at ${interface['mac']} on ${interface['name']}": }

When we run Puppet on this, we see the following notify in the output:

t@cookbook:~/.puppet/manifests$ puppet apply hash.pp
Notice: (192.168.0.1) at 52:54:00:4a:60:07 on etho

Hash values can be anything that you can assign to variables, strings, function calls, expressions, and even other hashes or arrays. Hashes are useful to store a bunch of information about a particular thing because by accessing each element of the hash using a key, we can quickly find the information for which we are looking.

You can declare literal arrays using square brackets, as follows:

define lunchprint() {
  notify { "Lunch included ${name}":}": }
}

$lunch = ['egg', 'beans', 'chips']
lunchprint { $lunch: }

Now, when we run Puppet on the preceding code, we see the following notice messages in the output:

t@mylaptop ~ $ puppet apply lunchprint.pp 
...
Notice: Lunch included chips
Notice: Lunch included beans
Notice: Lunch included egg

However, Puppet can also create arrays for you from strings, using the split function, as follows:

$menu = 'egg beans chips'
$items = split($menu, ' ')
lunchprint { $items: }

Running puppet apply against this new manifest, we see the same messages in the output:

t@mylaptop ~ $ puppet apply lunchprint2.pp 
...
Notice: Lunch included chips
Notice: Lunch included beans
Notice: Lunch included egg.

Note that split takes two arguments: the first argument is the string to be split. The second argument is the character to split on; in this example, a single space. As Puppet works its way through the string, when it encounters a space, it will interpret it as the end of one item and the beginning of the next. So, given the string 'egg beans chips', this will be split into three items.

The character to split on can be any character or string:

$menu = 'egg and beans and chips'
$items = split($menu, ' and ')

The character can also be a regular expression, for example, a set of alternatives separated by a | (pipe) character:

$lunch = 'egg:beans,chips'
$items = split($lunch, ':|,')