bash

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Use the bash resource to execute scripts using the Bash interpreter. This resource may also use any of the actions and properties that are available to the execute resource. Commands that are executed with this resource are (by their nature) not idempotent, as they are typically unique to the environment in which they are run. Use not_if and only_if to guard this resource for idempotence.

Note

The bash script resource (which is based on the script resource) is different from the ruby_block resource because Ruby code that is run with this resource is created as a temporary file and executed like other script resources, rather than run inline.

Syntax

A bash resource block executes scripts using Bash:

bash 'extract_module' do
  cwd ::File.dirname(src_filepath)
  code <<-EOH
    mkdir -p #{extract_path}
    tar xzf #{src_filename} -C #{extract_path}
    mv #{extract_path}/*/* #{extract_path}/
    EOH
  not_if { ::File.exist?(extract_path) }
end

where

  • cwd specifies the directory from which the command is run
  • code specifies the command to run

The full syntax for all of the properties that are available to the bash resource is:

bash 'name' do
  code                       String
  creates                    String
  cwd                        String
  environment                Hash
  flags                      String
  group                      String, Integer
  notifies                   # see description
  path                       Array
  returns                    Integer, Array
  subscribes                 # see description
  timeout                    Integer, Float
  user                       String, Integer
  umask                      String, Integer
  action                     Symbol # defaults to :run if not specified
end

where

  • bash is the resource
  • name is the name of the resource block
  • cwd is the location from which the command is run
  • action identifies the steps the chef-client will take to bring the node into the desired state
  • code, creates, cwd, environment, flags, group, path, returns, timeout, user, and umask are properties of this resource, with the Ruby type shown. See “Properties” section below for more information about all of the properties that may be used with this resource.

Actions

This resource has the following actions:

:nothing
Prevent a command from running. This action is used to specify that a command is run only when another resource notifies it.
:run
Default. Run a script.

Properties

This resource has the following properties:

code

Ruby Type: String

A quoted (” “) string of code to be executed.

creates

Ruby Type: String

Prevent a command from creating a file when that file already exists.

cwd

Ruby Type: String

The current working directory.

environment

Ruby Type: Hash

A Hash of environment variables in the form of ({"ENV_VARIABLE" => "VALUE"}). (These variables must exist for a command to be run successfully.)

flags

Ruby Type: String

One or more command line flags that are passed to the interpreter when a command is invoked.

group

Ruby Type: String, Integer

The group name or group ID that must be changed before running a command.

ignore_failure

Ruby Type: true, false | Default Value: false

Continue running a recipe if a resource fails for any reason.

notifies

Ruby Type: Symbol, ‘Chef::Resource[String]’

A resource may notify another resource to take action when its state changes. Specify a 'resource[name]', the :action that resource should take, and then the :timer for that action. A resource may notify more than one resource; use a notifies statement for each resource to be notified.

A timer specifies the point during the Chef Client run at which a notification is run. The following timers are available:

:before
Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.
:delayed
Default. Specifies that a notification should be queued up, and then executed at the end of the Chef Client run.
:immediate, :immediately
Specifies that a notification should be run immediately, per resource notified.

The syntax for notifies is:

notifies :action, 'resource[name]', :timer
path

Ruby Type: Array

An array of paths to use when searching for a command. These paths are not added to the command’s environment $PATH. The default value uses the system path.

Warning

For example:

bash 'mycommand' do
  environment 'PATH' => "/my/path/to/bin:#{ENV['PATH']}"
end
retries

Ruby Type: Integer | Default Value: 0

The number of times to catch exceptions and retry the resource.

retry_delay

Ruby Type: Integer | Default Value: 2

The retry delay (in seconds).

returns

Ruby Type: Integer, Array | Default Value: 0

The return value for a command. This may be an array of accepted values. An exception is raised when the return value(s) do not match.

subscribes

Ruby Type: Symbol, ‘Chef::Resource[String]’

A resource may listen to another resource, and then take action if the state of the resource being listened to changes. Specify a 'resource[name]', the :action to be taken, and then the :timer for that action.

Note that subscribes does not apply the specified action to the resource that it listens to - for example:

file '/etc/nginx/ssl/example.crt' do
   mode '0600'
   owner 'root'
end

service 'nginx' do
   subscribes :reload, 'file[/etc/nginx/ssl/example.crt]', :immediately
end

In this case the subscribes property reloads the nginx service whenever its certificate file, located under /etc/nginx/ssl/example.crt, is updated. subscribes does not make any changes to the certificate file itself, it merely listens for a change to the file, and executes the :reload action for its resource (in this example nginx) when a change is detected.

A timer specifies the point during the Chef Client run at which a notification is run. The following timers are available:

:before
Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.
:delayed
Default. Specifies that a notification should be queued up, and then executed at the end of the Chef Client run.
:immediate, :immediately
Specifies that a notification should be run immediately, per resource notified.

The syntax for subscribes is:

subscribes :action, 'resource[name]', :timer
timeout

Ruby Type: Integer, Float | Default Value: 3600

The amount of time (in seconds) a command is to wait before timing out.

user

Ruby Type: String, Integer

The user name or user ID that should be changed before running a command.

umask

Ruby Type: String, Integer

The file mode creation mask, or umask.

Guards

A guard property can be used to evaluate the state of a node during the execution phase of the chef-client run. Based on the results of this evaluation, a guard property is then used to tell the chef-client if it should continue executing a resource. A guard property accepts either a string value or a Ruby block value:

  • A string is executed as a shell command. If the command returns 0, the guard is applied. If the command returns any other value, then the guard property is not applied. String guards in a powershell_script run Windows PowerShell commands and may return true in addition to 0.
  • A block is executed as Ruby code that must return either true or false. If the block returns true, the guard property is applied. If the block returns false, the guard property is not applied.

A guard property is useful for ensuring that a resource is idempotent by allowing that resource to test for the desired state as it is being executed, and then if the desired state is present, for the chef-client to do nothing.

Attributes

The following properties can be used to define a guard that is evaluated during the execution phase of the chef-client run:

not_if
Prevent a resource from executing when the condition returns true.
only_if
Allow a resource to execute only if the condition returns true.

Arguments

The following arguments can be used with the not_if or only_if guard properties:

:user

Specify the user that a command will run as. For example:

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

Specify the group that a command will run as. For example:

not_if 'grep adam /etc/passwd', :group => 'adam'
:environment

Specify a Hash of environment variables to be set. For example:

not_if 'grep adam /etc/passwd', :environment => {
  'HOME' => '/home/adam'
}
:cwd

Set the current working directory before running a command. For example:

not_if 'grep adam passwd', :cwd => '/etc'
:timeout

Set a timeout for a command. For example:

not_if 'sleep 10000', :timeout => 10

Examples

The following examples demonstrate various approaches for using resources in recipes. If you want to see examples of how Chef uses resources in recipes, take a closer look at the cookbooks that Chef authors and maintains: https://github.com/chef-cookbooks.

Use a named provider to run a script

bash 'install_something' do
  user 'root'
  cwd '/tmp'
  code <<-EOH
  wget http://www.example.com/tarball.tar.gz
  tar -zxf tarball.tar.gz
  cd tarball
  ./configure
  make
  make install
  EOH
end

Install a file from a remote location using bash

The following is an example of how to install the foo123 module for Nginx. This module adds shell-style functionality to an Nginx configuration file and does the following:

  • Declares three variables
  • Gets the Nginx file from a remote location
  • Installs the file using Bash to the path specified by the src_filepath variable
# the following code sample is similar to the ``upload_progress_module``
# recipe in the ``nginx`` cookbook:
# https://github.com/chef-cookbooks/nginx

src_filename = "foo123-nginx-module-v#{
  node['nginx']['foo123']['version']
}.tar.gz"
src_filepath = "#{Chef::Config['file_cache_path']}/#{src_filename}"
extract_path = "#{
  Chef::Config['file_cache_path']
  }/nginx_foo123_module/#{
  node['nginx']['foo123']['checksum']
}"

remote_file 'src_filepath' do
  source node['nginx']['foo123']['url']
  checksum node['nginx']['foo123']['checksum']
  owner 'root'
  group 'root'
  mode '0755'
end

bash 'extract_module' do
  cwd ::File.dirname(src_filepath)
  code <<-EOH
    mkdir -p #{extract_path}
    tar xzf #{src_filename} -C #{extract_path}
    mv #{extract_path}/*/* #{extract_path}/
    EOH
  not_if { ::File.exist?(extract_path) }
end

Install an application from git using bash

The following example shows how Bash can be used to install a plug-in for rbenv named ruby-build, which is located in git version source control. First, the application is synchronized, and then Bash changes its working directory to the location in which ruby-build is located, and then runs a command.

 git "#{Chef::Config[:file_cache_path]}/ruby-build" do
   repository 'git://github.com/sstephenson/ruby-build.git'
   reference 'master'
   action :sync
 end

 bash 'install_ruby_build' do
   cwd '#{Chef::Config[:file_cache_path]}/ruby-build'
   user 'rbenv'
   group 'rbenv'
   code <<-EOH
     ./install.sh
     EOH
   environment 'PREFIX' => '/usr/local'
end

To read more about ruby-build, see here: https://github.com/sstephenson/ruby-build.

Store certain settings

The following recipe shows how an attributes file can be used to store certain settings. An attributes file is located in the attributes/ directory in the same cookbook as the recipe which calls the attributes file. In this example, the attributes file specifies certain settings for Python that are then used across all nodes against which this recipe will run.

Python packages have versions, installation directories, URLs, and checksum files. An attributes file that exists to support this type of recipe would include settings like the following:

default['python']['version'] = '2.7.1'

if python['install_method'] == 'package'
  default['python']['prefix_dir'] = '/usr'
else
  default['python']['prefix_dir'] = '/usr/local'
end

default['python']['url'] = 'http://www.python.org/ftp/python'
default['python']['checksum'] = '80e387...85fd61'

and then the methods in the recipe may refer to these values. A recipe that is used to install Python will need to do the following:

  • Identify each package to be installed (implied in this example, not shown)
  • Define variables for the package version and the install_path
  • Get the package from a remote location, but only if the package does not already exist on the target system
  • Use the bash resource to install the package on the node, but only when the package is not already installed
#  the following code sample comes from the ``oc-nginx`` cookbook on |github|: https://github.com/cookbooks/oc-nginx

version = node['python']['version']
install_path = "#{node['python']['prefix_dir']}/lib/python#{version.split(/(^\d+\.\d+)/)[1]}"

remote_file "#{Chef::Config[:file_cache_path]}/Python-#{version}.tar.bz2" do
  source "#{node['python']['url']}/#{version}/Python-#{version}.tar.bz2"
  checksum node['python']['checksum']
  mode '0755'
  not_if { ::File.exist?(install_path) }
end

bash 'build-and-install-python' do
  cwd Chef::Config[:file_cache_path]
  code <<-EOF
    tar -jxvf Python-#{version}.tar.bz2
    (cd Python-#{version} && ./configure #{configure_options})
    (cd Python-#{version} && make && make install)
  EOF
  not_if { ::File.exist?(install_path) }
end