Language: Reserved words and acceptable names

Reserved words

Several words in the Puppet language are reserved. This means they:

Cannot be used as bare word strings — you must quote these words if you wish to use them as strings.
Cannot be used as names for custom functions.
Cannot be used as names for classes.
Cannot be used as names for custom resource types or defined resource types.

The following words are reserved:

and — expression operator
application — language keyword
attr — reserved for future use
case — language keyword
class — language keyword
component — reserved
consumes — language keyword
default — language keyword
define — language keyword
else — language keyword
elsif — language keyword
environment — reserved for symbolic namespace use
false — boolean value
function — language keyword
if — language keyword
import — former language keyword (now removed)
in — expression operator
inherits — language keyword
node — language keyword
or — expression operator
private — reserved for future use
produces — language keyword
regexp — reserved
site — language keyword
true — boolean value
type — language keyword
undef — special value
unit — reserved
unless — language keyword

Additionally:

You cannot use the name of any existing resource type or function as the name of a function.
You cannot use the name of any existing resource type as the name of a defined type.
You shouldn’t use the name of any existing data type (e.g. integer) as the name of a defined type, as this will make it inconvenient to interact with. (You can’t directly reference a resource of that defined type with only its uppercased name — instead of writing a resource reference like Integer[title], you would have to use Resource[integer, title].)

Reserved class names

The following are built-in namespaces used by Puppet and so must not be used as class names:

main — Puppet automatically creates a main class, which contains any resources not contained by any other class.
settings — The automatically created settings namespace contains variables with the settings available to the compiler (that is, the Puppet master’s settings).

Additionally, the names of data types can’t be used as class names:

any, Any
array, Array
boolean, Boolean
catalogentry, catalogEntry, CatalogEntry
class, Class
collection, Collection
callable, Callable
data, Data
default, Default
enum, Enum
float, Float
hash, Hash
integer, Integer
numeric, Numeric
optional, Optional
pattern, Pattern
resource, Resource
runtime, Runtime
scalar, Scalar
string, String
struct, Struct
tuple, Tuple
type, Type
undef, Undef
variant, Variant

Reserved variable names

The following variable names are reserved. Unless otherwise noted, you can’t assign values to them or use them as parameters in classes or defined types.

$0, $1, and every other variable name consisting only of digits. These regex capture variables are automatically set by regular expressions used in conditional statements, and their values do not persist outside their associated code block or selector value. Puppet will raise an error if you try to assign to these variables.
Puppet’s built-in variables and facts are reserved at top scope, but can be safely re-used at node or local scope.
$trusted and $facts are reserved for facts and cannot be reassigned at local scopes.
$server_facts (if enabled) is reserved for trusted server facts and cannot be reassigned at local scopes.
$title is reserved for the title of a class or defined type.
$name is a synonym for $title.

Acceptable characters in names

Puppet limits the characters you can use when naming language constructs.

Note: In some cases, names containing unsupported characters will still work. These cases should be considered bugs, and might cease to work at any time. Removal of these bug cases will not be limited to major releases.

Variables

Variable names begin with a $ (dollar sign) and are case-sensitive.

Most variable names must start with a lowercase letter or an underscore. The exception is regex capture variables, which are named with only numbers.

Variable names can include:

Uppercase and lowercase letters
Numbers
Underscores (_)

If the first character is an underscore, that variable should only be accessed from its own local scope; using qualified variable names where any namespace segment begins with _ is deprecated.

Note that some variable names are reserved.

Qualified Variable Names

Qualified variable names are prefixed with the name of their scope and the :: (double colon) namespace separator. (For example, the $vhostdir variable from the apache::params class would be $apache::params::vhostdir.)

Optionally, the name of the very first namespace can be empty, representing the top namespace. In previous versions of the Puppet language, this was often used to work around bugs, but it’s not necessary in this version. The main use is to indicate to readers that you’re accessing a top-scope variable, e.g. $::is_virtual.

Regular Expressions For Variable Names

Short variable names should match the following regular expression:

\A\$[a-z0-9_][a-zA-Z0-9_]*\Z

Qualified variable names should match the following regular expression:

\A\$([a-z][a-z0-9_]*)?(::[a-z][a-z0-9_]*)*::[a-z0-9_][a-zA-Z0-9_]*\Z

Classes and defined resource types

The names of classes and defined resource types can consist of one or more namespace segments. Each namespace segment must begin with a lowercase letter and can include:

Lowercase letters
Uppercase letters
Digits
Underscores

In other words, namespace segments should match the following Ruby regular expression:

\A[a-z]\w*\Z

The one exception is the top namespace, whose name is the empty string.

Multiple namespace segments can be joined together in a class or defined type name with the :: (double colon) namespace separator.

For example, class names with multiple namespaces should match the following Ruby regular expression:

\A((::)?[a-z]\w*)(::[a-z]\w*)*\z

Note that some class names are reserved, and reserved words cannot be used as class or defined type names.

Additionally, you cannot use the name <MODULE NAME>::init for a class or defined type. This is because init.pp is a reserved filename, which should contain a class named after the module.

Modules

Module names obey the same rules as individual namespace segments (like in a class or defined type name). That is, they must begin with a lowercase letter and can include:

Lowercase letters
Uppercase letters.
Digits
Underscores

Module names should match the following Ruby regular expression:

\A[a-z][a-z0-9_]*\Z

Note that reserved words and reserved class names cannot be used as module names.

Parameters

Class and defined type parameters begin with a $ (dollar sign), and their first non-$ character must be a lowercase letter. They can include:

Lowercase letters
Uppercase letters
Digits
Underscores

Parameter names should match the following Ruby regular expression:

\A\$[a-z][a-z0-9_]*\Z

Resources

Resource titles can contain any characters whatsoever. They are case-sensitive.

Resource names (or namevars) might be limited by the underlying system being managed. (E.g., most systems have limits on the characters allowed in the name of a user account.) The user is generally responsible for knowing the name limits on the platforms they manage.

Nodes

The set of characters allowed in node names is undefined in this version of Puppet. For best future compatibility, you should limit node names to letters, digits, periods, underscores, and dashes. (That is, node names should match /\A[a-z0-9._-]+\Z/.)

Environments

Environment names can contain lowercase letters, numbers, and underscores. That is, they must match the following Ruby regular expression:

\A[a-z0-9_]+\Z

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