examples.md

(ARM-2) Iteration Examples

This document contains examples of the Recommended Implementation.

Update

The examples have been updated to Puppet 3.4 w.r.t renamed iterative functions.

Creating an Array by appending to each element of another Array

Question from mailing list:

How can I append "/var/bricks" to each item in the array? Lack of a looping construct makes this challenging in puppet, such that: brick_array = ['gfs01:/var/bricks', 'gfs02:/var/bricks', ... ] ?

Here is how:

$nodes = ['gfs01' ,'gfs02', 'gfs03', 'gfs04']
$brick_store = "/var/bricks"
$brick_array = $nodes.map |$x| { "$x:$brick_store" }

Combining Two Structures

From the mailinglist:

I need to generate a file with this content:

/bin/mount --bind /home/some/path/ /home/someuser/www
/bin/mount --bind /home/comple/tely/different/path/ /home/differentuser/www
/bin/mount --bind /home/another/path/ /home/anotheruser/www

For each row I need to insert two variables, the path (different per user), and .../user/www.

By reducing a hash

$data = {
  'someuser'     => 'some/path', 
  'differentuser'=>'complete/tely/different/path', 
  'anotheruser'  => 'another/path'
}
$content = $data.reduce("") |$memo, $x| { "$memo
/bin/mount --bind /home/${x[1]}/ /home/${x[1]}/www" }

# content contains the desired text (although with a blank line first)

By map and join

This can also be implemented as mapping to an array, and applying the standard library join function on the result (joining entries with a new line).

# function call style
$content = join($data.map |$x| "/bin/mount --bind /home/${$x[1]}/ /home/${x[0]}/www" }, "\n")

# or method call style
$content = $data.map |$x| "/bin/mount --bind /home/${$x[1]}/ /home/${x[0]}/www" }.join("\n")

zip of two arrays, map, and join

If the structure is in two arrays, the stdlib function zip can be used to combine them:

$users = ['someuser', 'differentuser', 'anotheruser']
$paths = ['some/path', 'complete/tely/different/path', 'another/path']
$content = zip($users, $paths).map |$x| "/bin/mount --bind /home/${x[1]}/ /home/${x[0]}/www" }.join("\n")

slize one array, map, and join

If the structure is in one array, the slice function (in this ARM) can be used:

$users = ['someuser', 'some/path', 'differentuser', 'complete/tely/different/path', 'anotheruser', 'another/path']
$content = $users.slice(2).map |$x| { "/bin/mount --bind /home/${paths[$x]}/ /home/$x/www" }.join("\n")

Iterating over an Array - Creating Resources

Question: I have a list of users and need to create a file resource for each user and set the owner to that user. (Sure, I can pass an array as title, but I need to also set owner...)

Here is how this can be done:

$usernames.each |$x| { file { "/home/$x/.somerc": owner => $x } }

Iterating over pairs in an array or hash

Question: I have an array with user-names and modes, I need to create a file resource with corresponding mode.

Here is how, using slice function to pick pairs from the array

$users_with_mode = ['fred', 0666, 'mary', 0777 ]
$users_with_mode.slice(2) |$x| {
  file {"/home/{$x[0]}/.somerc":
    owner => $x[0],
    mode  => $x[1]
  }
}

And if they are in a hash?

Easier, that can be written as:

$users_with_mode = ['fred' => 0666, 'mary' => 0777 ]
$users_with_mode.each |$user, $mode| {
  file {"/home/$user/.somerc":
    owner => $user,
    mode  => $mode
  }
}

Creating, Collecting, and Relating Resources

$r1 = $a1.map |$x| {file {"/somewhere/$x": owner => $x}}
$r2 = $a2.map |$x| {file {"/elsewhere/$x": owner => $x}}
$r1 -> $r2

or

$a1.map |$x| { file {"/somewhere/$x": owner => $x}} ->
  $a2.map |$x| { file {"/elsewhere/$x": owner => $x}}

Filtering Data Before Creating a resource

$a.filter |$x| { $x =~ /com$/ }.each |$x| {
  file { "/somewhere/$x":
    owner => $x
  }
}

Including Classes Derived From Facts

From user group:
Variable $roles contains names of roles (obtained via a fact), and the need is to map these to inclusion of classes.

Here is a very simple interpolation of the name, but could naturally use a hash lookup or similar.

$roles.each |$x| { 
  include "our_$x"
}