Ruby is a simple programming language:
Ruby is also a powerful and complete programming language:
This section covers the basics of Ruby.
Many people who are new to Ruby often find that it doesn’t take very long to get up to speed with the basics. For example, it’s useful to know how to check the syntax of a Ruby file, such as the contents of a cookbook named my_cookbook.rb:
$ ruby -c my_cookbook_file.rb
to return:
Syntax OK
Use a comment to explain code that exists in a cookbook or recipe. Anything after a # is a comment.
# This is a comment.
Assign a local variable:
x = 1
Do some basic arithmetic:
1 + 2 # => 3 2 * 7 # => 14 5 / 2 # => 2 (because both arguments are whole numbers) 5 / 2.0 # => 2.5 (because one of the numbers had a decimal place) 1 + (2 * 3) # => 7 (you can use parens to group expressions)
Work with strings:
'single quoted' # => "single quoted" "double quoted" # => "double quoted" 'It\'s alive!' # => "It's alive!" (the \ is an escape character) '1 + 2 = 5' # => "1 + 2 = 5" (numbers surrounded by quotes behave like strings)
Convert a string to uppercase or lowercase. For example, a hostname named “Foo”:
node['hostname'].downcase # => "foo" node['hostname'].upcase # => "FOO"
Embed Ruby in a string:
x = 'Bob'
"Hi, #{x}" # => "Hi, Bob"
'Hello, #{x}' # => "Hello, \#{x}" Notice that single quotes don't work with #{} Use the backslash character (\) as an escape character when quotes must appear within strings. However, you do not need to escape single quotes inside double quotes. For example:
'It\'s alive!' # => "It's alive!" "Won\'t you read Grant\'s book?" # => "Won't you read Grant's book?"
When strings have quotes within quotes, use double quotes (" ") on the outer quotes, and then single quotes (' ') for the inner quotes. For example:
Chef::Log.info("Loaded from aws[#{aws['id']}]") "node['mysql']['secretpath']"
"#{ENV['HOME']}/chef.txt" antarctica_hint = hint?('antarctica')
if antarctica_hint['snow']
"There are #{antarctica_hint['penguins']} penguins here."
else
'There is no snow here, and penguins like snow.'
end Work with basic truths:
true # => true
false # => false
nil # => nil
0 # => true ( the only false values in Ruby are false
# and nil; in other words: if it exists in Ruby,
# even if it exists as zero, then it is true.)
1 == 1 # => true ( == tests for equality )
1 == true # => false ( == tests for equality ) Work with basic untruths (! means not!):
!true # => false !false # => true !nil # => true 1 != 2 # => true (1 is not equal to 2) 1 != 1 # => false (1 is not not equal to itself)
Convert something to either true or false (!! means not not!!):
!!true # => true !!false # => false !!nil # => false (when pressed, nil is false) !!0 # => true (zero is NOT false).
Create lists using arrays:
x = ['a', 'b', 'c'] # => ["a", "b", "c"] x[0] # => "a" (zero is the first index) x.first # => "a" (see?) x.last # => "c" x + ['d'] # => ["a", "b", "c", "d"] x # => ["a", "b", "c"] ( x is unchanged) x = x + ['d'] # => ["a", "b", "c", "d"] x # => ["a", "b", "c", "d"]
The %w syntax is a Ruby shortcut for creating an array without requiring quotes and commas around the elements.
For example:
if %w{debian ubuntu}.include?(node['platform'])
# do debian/ubuntu things with the Ruby array %w{} shortcut
end When %w syntax uses a variable, such as |foo|, double quoted strings should be used.
Right:
%w{openssl.cnf pkitool vars Rakefile}.each do |foo|
template "/etc/openvpn/easy-rsa/#{foo}" do
source "#{foo}.erb"
...
end
end Wrong:
%w{openssl.cnf pkitool vars Rakefile}.each do |foo|
template '/etc/openvpn/easy-rsa/#{foo}' do
source '#{foo}.erb'
...
end
end Example
WiX includes serveral tools – such as candle (preprocesses and compiles source files into object files), light (links and binds object files to an installer database), and heat (harvests files from various input formats). The following example uses a whitespace array and the InSpec file audit resource to verify if these three tools are present:
%w(
candle.exe
heat.exe
light.exe
).each do |utility|
describe file("C:/wix/#{utility}") do
it { should be_file }
end
end A Hash is a list with keys and values. Sometimes they don’t have a set order:
h = {
'first_name' => "Bob",
'last_name' => "Jones"
} And sometimes they do. For example, first name then last name:
h.keys # => ["first_name", "last_name"] h['first_name'] # => "Bob" h['last_name'] # => "Jones" h['age'] = 23 h.keys # => ["first_name", "age", "last_name"] h.values # => ["Jones", "Bob", 23]
Use Perl-style regular expressions:
'I believe' =~ /I/ # => 0 (matches at the first character) 'I believe' =~ /lie/ # => 4 (matches at the 5th character) 'I am human' =~ /bacon/ # => nil (no match - bacon comes from pigs) 'I am human' !~ /bacon/ # => true (correct, no bacon here) /give me a ([0-9]+)/ =~ 'give me a 7' # => 0 (matched)
Use conditions! For example, an if statement
if false # this won't happen elsif nil # this won't either else # code here will run though end
or a case statement:
x = 'dog' case x when 'fish' # this won't happen when 'dog', 'cat', 'monkey' # this will run else # the else is an optional catch-all end
An if statement can be used to specify part of a recipe to be used when certain conditions are met. else and elseif statements can be used to handle situations where either the initial condition is not met or when there are other possible conditions that can be met. Since this behavior is 100% Ruby, do this in a recipe the same way here as anywhere else.
For example, using an if statement with the platform node attribute:
if node['platform'] == 'ubuntu' # do ubuntu things end
A case statement can be used to handle a situation where there are a lot of conditions. Use the when statement for each condition, as many as are required.
For example, using a case statement with the platform node attribute:
case node['platform'] when 'debian', 'ubuntu' # do debian/ubuntu things when 'redhat', 'centos', 'fedora' # do redhat/centos/fedora things end
For example, using a case statement with the platform_family node attribute:
case node['platform_family'] when 'debian' # do things on debian-ish platforms (debian, ubuntu, linuxmint) when 'rhel' # do things on RHEL platforms (redhat, centos, scientific, etc) end
Call a method on something with .method_name():
x = 'My String'
x.split(' ') # => ["My", "String"]
x.split(' ').join(', ') # => "My, String" Define a method (or a function, if you like):
def do_something_useless( first_argument, second_argument)
puts "You gave me #{first_argument} and #{second_argument}"
end
do_something_useless( 'apple', 'banana')
# => "You gave me apple and banana"
do_something_useless 1, 2
# => "You gave me 1 and 2"
# see how the parens are optional if there's no confusion about what to do Use the Ruby File class in a recipe. Because Chef has the file resource, use File to use the Ruby File class. For example:
execute 'apt-get-update' do
command 'apt-get update'
ignore_failure true
only_if { apt_installed? }
not_if { File.exist?('/var/lib/apt/periodic/update-success-stamp') }
end Use :include to include another Ruby class. For example:
::Chef::Recipe.send(:include, Opscode::OpenSSL::Password)
In non-Chef Ruby, the syntax is include (without the : prefix), but without the : prefix the chef-client will try to find a provider named include. Using the : prefix tells the chef-client to look for the specified class that follows.
The include? method can be used to ensure that a specific parameter is included before an action is taken. For example, using the include? method to find a specific parameter:
if ['debian', 'ubuntu'].include?(node['platform']) # do debian/ubuntu things end
or:
if %w{rhel}.include?(node['platform_family'])
# do RHEL things
end Chef::Log extends Mixlib::Log and will print log entries to the default logger that is configured for the machine on which the chef-client is running. (To create a log entry that is built into the resource collection, use the log resource instead of Chef::Log.)
The following log levels are supported:
| Log Level | Syntax |
|---|---|
| Debug | Chef::Log.debug('string') |
| Error | Chef::Log.error('string') |
| Fatal | Chef::Log.fatal('string') |
| Info | Chef::Log.info('string') |
| Warn | Chef::Log.warn('string') |
Note
The parentheses are optional, e.g. Chef::Log.info 'string' may be used instead of Chef::Log.info('string').
The following examples show using Chef::Log entries in a recipe.
The following example shows a series of fatal Chef::Log entries:
unless node['splunk']['upgrade_enabled']
Chef::Log.fatal('The chef-splunk::upgrade recipe was added to the node,')
Chef::Log.fatal('but the attribute `node["splunk"]["upgrade_enabled"]` was not set.')
Chef::Log.fatal('I am bailing here so this node does not upgrade.')
raise
end
service 'splunk_stop' do
service_name 'splunk'
supports :status => true
provider Chef::Provider::Service::Init
action :stop
end
if node['splunk']['is_server']
splunk_package = 'splunk'
url_type = 'server'
else
splunk_package = 'splunkforwarder'
url_type = 'forwarder'
end
splunk_installer splunk_package do
url node['splunk']['upgrade']["#{url_type}_url"]
end
if node['splunk']['accept_license']
execute 'splunk-unattended-upgrade' do
command "#{splunk_cmd} start --accept-license --answer-yes"
end
else
Chef::Log.fatal('You did not accept the license (set node["splunk"]["accept_license"] to true)')
Chef::Log.fatal('Splunk is stopped and cannot be restarted until the license is accepted!')
raise
end The full recipe is the upgrade.rb recipe of the chef-splunk cookbook that is maintained by Chef.
The following example shows using multiple Chef::Log entry types:
...
begin
aws = Chef::DataBagItem.load(:aws, :main)
Chef::Log.info("Loaded AWS information from DataBagItem aws[#{aws['id']}]")
rescue
Chef::Log.fatal("Could not find the 'main' item in the 'aws' data bag")
raise
end
... The full recipe is in the ebs_volume.rb recipe of the database cookbook that is maintained by Chef.
This section covers best practices for cookbook and recipe authoring.
Although not strictly a Chef style thing, please always ensure your user.name and user.email are set properly in your .gitconfig file.
user.name should be your given name (e.g., “Julian Dunn”)user.email should be an actual, working e-mail addressThis will prevent commit log entries similar to "guestuser <[email protected]>", which are unhelpful.
Cookbook and custom resource names should contain only alphanumeric characters. A hyphen (-) is a valid character and may be used in cookbook and custom resource names, but it is discouraged. The chef-client will return an error if a hyphen is not converted to an underscore (_) when referencing from a recipe the name of a custom resource in which a hyphen is located.
Use a short organizational prefix for application cookbooks that are part of your organization. For example, if your organization is named SecondMarket, use sm as a prefix: sm_postgresql or sm_httpd.
Good cookbook examples:
Name things uniformly for their system and component. For example:
node['foo']['bar']
foo::bar
foo-bar
foo/bar (if specific to component), foo (if not). For example: /var/log/foo/bar.Name attributes after the recipe in which they are primarily used. e.g. node['postgresql']['server'].
Follow this order for information in each resource declaration:
For example:
template '/tmp/foobar.txt' do
source 'foobar.txt.erb'
owner 'someuser'
group 'somegroup'
mode '0644'
variables(
:foo => 'bar'
)
notifies :reload, 'service[whatever]'
action :create
end Always specify the file mode with a quoted 3-5 character string that defines the octal mode:
mode '755'
mode '0755'
mode 00755
A resource declaration does not require the action to be specified because the chef-client will apply the default action for a resource automatically if it’s not specified within the resource block. For example:
package 'monit'
will install the monit package because the :install action is the default action for the package resource.
However, if readability of code is desired, such as ensuring that a reader understands what the default action is for a custom resource or stating the action for a resource whose default may not be immediately obvious to the reader, specifying the default action is recommended:
ohai 'apache_modules' do action :reload end
Prefer strings over symbols, because they’re easier to read and you don’t need to explain to non-Rubyists what a symbol is. Please retrofit old cookbooks as you come across them.
Right:
default['foo']['bar'] = 'baz'
Wrong:
default[:foo][:bar] = 'baz'
Use single-quoted strings in all situations where the string doesn’t need interpolation.
When %w syntax uses a variable, such as |foo|, double quoted strings should be used.
Right:
%w{openssl.cnf pkitool vars Rakefile}.each do |foo|
template "/etc/openvpn/easy-rsa/#{foo}" do
source "#{foo}.erb"
...
end
end Wrong:
%w{openssl.cnf pkitool vars Rakefile}.each do |foo|
template '/etc/openvpn/easy-rsa/#{foo}' do
source '#{foo}.erb'
...
end
end Always use mixlib-shellout to shell out. Never use backticks, Process.spawn, popen4, or anything else!
The mixlib-shellout module provides a simplified interface to shelling out while still collecting both standard out and standard error and providing full control over environment, working directory, uid, gid, etc.
Starting with chef-client version 12.0 you can use the shell_out, shell_out! and shell_out_with_system_locale Recipe DSL methods to interface directly with mixlib-shellout.
Avoid the following patterns:
node.set / normal_attributes - Avoid using attributes at normal precedence since they are set directly on the node object itself, rather than implied (computed) at runtime.node.set_unless - Can lead to weird behavior if the node object had something set. Avoid unless altogether necessary (one example where it’s necessary is in node['postgresql']['server']['password'])node.run_list.include?('foo') i.e. branching in recipes based on what’s in the node’s run-list. Better and more readable to use a feature flag and set its precedence appropriately.node['foo']['bar'] i.e. setting normal attributes without specifying precedence. This is deprecated in Chef 11, so either use node.set['foo']['bar'] to replace its precedence in-place or choose the precedence to suit.A recipe should be clean and well-commented. For example:
###########
# variables
###########
connection_info = {
host: '127.0.0.1',
port: '3306',
username: 'root',
password: 'm3y3sqlr00t'
}
#################
# Mysql resources
#################
mysql_service 'default' do
port '3306'
initial_root_password 'm3y3sqlr00t'
action [:create, :start]
end
mysql_database 'wordpress_demo' do
connection connection_info
action :create
end
mysql_database_user 'wordpress_user' do
connection connection_info
database_name 'wordpress_demo'
password 'w0rdpr3ssdem0'
privileges [:create, :delete, :select, :update, :insert]
action :grant
end
##################
# Apache resources
##################
httpd_service 'default' do
listen_ports %w(80)
mpm 'prefork'
action [:create, :start]
end
httpd_module 'php' do
notifies :restart, 'httpd_service[default]'
action :create
end
###############
# Php resources
###############
# php_runtime 'default' do
# action :install
# end
package 'php-gd' do
action :install
end
package 'php-mysql' do
action :install
end
directory '/etc/php.d' do
action :create
end
template '/etc/php.d/mysql.ini' do
source 'mysql.ini.erb'
action :create
end
httpd_config 'php' do
source 'php.conf.erb'
notifies :restart, 'httpd_service[default]'
action :create
end
#####################
# wordpress resources
#####################
directory '/srv/wordpress_demo' do
user 'apache'
recursive true
action :create
end
tar_extract 'https://wordpress.org/wordpress-4.1.tar.gz' do
target_dir '/srv/wordpress_demo'
tar_flags ['--strip-components 1']
user 'apache'
creates '/srv/wordpress_demo/index.php'
action :extract
end
directory '/srv/wordpress_demo/wp-content' do
user 'apache'
action :create
end
httpd_config 'wordpress' do
source 'wordpress.conf.erb'
variables(
servername: 'wordpress',
server_aliases: %w(computers.biz www.computers.biz),
document_root: '/srv/wordpress_demo'
)
notifies :restart, 'httpd_service[default]'
action :create
end
template '/srv/wordpress_demo/wp-config.php' do
source 'wp-config.php.erb'
owner 'apache'
variables(
db_name: 'wordpress_demo',
db_user: 'wordpress_user',
db_password: 'w0rdpr3ssdem0',
db_host: '127.0.0.1',
db_prefix: 'wp_',
db_charset: 'utf8',
auth_key: 'You should probably use randomly',
secure_auth_key: 'generated strings. These can be hard',
logged_in_key: 'coded, pulled from encrypted databags,',
nonce_key: 'or a ruby function that accessed an',
auth_salt: 'arbitrary data source, such as a password',
secure_auth_salt: 'vault. Node attributes could work',
logged_in_salt: 'as well, but you take special care',
nonce_salt: 'so they are not saved to your chef-server.',
allow_multisite: 'false'
)
action :create
end This section covers things that should be avoided when authoring cookbooks and recipes.
Use node.default (or maybe node.override) instead of node.set because node.set is an alias for node.normal. Normal data is persisted on the node object. Therefore, using node.set will persist data in the node object. If the code that uses node.set is later removed, if that data has already been set on the node, it will remain.
Normal and override attributes are cleared at the start of the chef-client run, and are then rebuilt as part of the run based on the code in the cookbooks and recipes at that time.
node.set (and node.normal) should only be used to do something like generate a password for a database on the first chef-client run, after which it’s remembered (instead of persisted). Even this case should be avoided, as using a data bag is the recommended way to store this type of data.
This section covers best practices for cookbook and recipe authoring.
All cookbooks should pass Foodcritic rules before being uploaded.
$ foodcritic -f all your-cookbook
should return nothing.
To learn more about Ruby, see the following:
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https://docs-archive.chef.io/release/12-13/ruby.html