bash Resource

Edit this page in the Chef repository

Resources Reference page

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.

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
  path                       Array
  returns                    Integer, Array
  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 given to the resource block.
• action identifies which steps Chef Infra 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

The bash resource has the following actions:

:nothing

This resource block does not act unless notified by another resource to take action. Once notified, this resource block either runs immediately or is queued up to run at the end of a Chef Infra Client run.

:run

Default. Run a script.

Properties

The bash resource has the following properties:

code

Ruby Type: String | REQUIRED

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 from which the command will be run.

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.

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.

timeout

Ruby Type: Integer, String, 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.

Common Resource Functionality

Chef resources include common properties, notifications, and resource guards.

Common Properties

The following properties are common to every resource:

compile_time

Ruby Type: true, false | Default Value: false

Control the phase during which the resource is run on the node. Set to true to run while the resource collection is being built (the compile phase). Set to false to run while Chef Infra Client is configuring the node (the converge phase).

ignore_failure

Ruby Type: true, false, :quiet | Default Value: false

Continue running a recipe if a resource fails for any reason. :quiet will not display the full stack trace and the recipe will continue to run if a resource fails.

retries

Ruby Type: Integer | Default Value: 0

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

retry_delay

Ruby Type: Integer | Default Value: 2

The retry delay (in seconds).

sensitive

Ruby Type: true, false | Default Value: false

Ensure that sensitive resource data is not logged by Chef InfraClient.

Notifications

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.

If the referenced resource does not exist, an error is raised. In contrast, subscribes will not fail if the source resource is not found.

A timer specifies the point during a Chef Infra 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 a Chef Infra 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

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.

If the other resource does not exist, the subscription will not raise an error. Contrast this with the stricter semantics of notifies, which will raise an error if the other resource does not exist.

A timer specifies the point during a Chef Infra 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 a Chef Infra 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

Guards

A guard property can be used to evaluate the state of a node during the execution phase of a Chef Infra Client run. Based on the results of this evaluation, a guard property is then used to tell Chef Infra 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 Chef Infra Client to do nothing.

The following properties can be used to define a guard that is evaluated during the execution phase of a Chef Infra 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.

Examples

The following examples demonstrate various approaches for using the bash resource in recipes:

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'
  revision '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