Looking up data with Hiera

You can combine these arguments in the following ways:

• lookup( <NAME>, [<VALUE TYPE>], [<MERGE BEHAVIOR>], [<DEFAULT VALUE>] )

• lookup( [<NAME>], <OPTIONS HASH> )

• lookup( as above ) |$key| { <VALUE> } # lambda returns a default value

Arguments accepted by lookup:

• <NAME> (String or Array) - The name of the key to look up. This can also be an array of keys. If Hiera doesn't find anything for the first key, it tries with the subsequent ones, only resorting to a default value if none of them succeed.
• <VALUE TYPE> (data Type) - A data type that must match the retrieved value; if not, the lookup (and catalog compilation) fails. Defaults to Data which accepts any normal value.
• <MERGE BEHAVIOR> (String or Hash; see Merge behaviors) - Whether and how to combine multiple values. If present, this overrides any merge behavior specified in the data sources. Defaults to no value; Hiera uses merge behavior from the data sources if present, otherwise it does a first-found lookup.
• <DEFAULT VALUE> (any normal value) - If present, lookup returns this when it can't find a normal value. Default values are never merged with found values. Like a normal value, the default must match the value type. Defaults to no value; if Hiera can't find a normal value, the lookup (and compilation) fails.
• <OPTIONS HASH> (Hash) - Alternate way to set the arguments above, plus some less common additional options. If you pass an options hash, you can't combine it with any regular arguments (except <NAME>). An options hash can have the following keys:
  • 'name' - Same as <NAME> (argument 1). You can pass this as an argument or in the hash, but not both.
  • 'value_type' - Same as <VALUE TYPE>.
  • 'merge' - Same as <MERGE BEHAVIOR>.
  • 'default_value' - Same as <DEFAULT VALUE> .
  • 'default_values_hash' (Hash) - A hash of lookup keys and default values. If Hiera can't find a normal value, it checks this hash for the requested key before giving up. You can combine this with default_value or a lambda, which is used if the key isn't present in this hash. Defaults to an empty hash.
  • 'override' (Hash) - A hash of lookup keys and override values. Puppet checks for the requested key in the overrides hash first. If found, it returns that value as the final value, ignoring merge behavior. Defaults to an empty hash.
  • lookup - can take a lambda, which must accept a single parameter. This is yet another way to set a default value for the lookup; if no results are found, Puppet passes the requested key to the lambda and use its result as the default value.

Examples:

(Still works, but deprecated)

hiera('some::key', 'the default value')

(Recommended) 

lookup('some::key', undef, undef, 'the default value')

Look up a key and returning the first value found:

lookup('ntp::service_name')

A unique merge lookup of class names, then adding all of those classes to the catalog:

lookup('classes', Array[String], 'unique').include

A deep hash merge lookup of user data, but letting higher priority sources remove values by prefixing them with:

lookup( { 'name'  => 'users',
          'merge' => {
            'strategy'        => 'deep',
            'knockout_prefix' => '--',
          },
})

To look up key_name using the Puppet Server node’s facts:

$ puppet lookup key_name

To look up key_name with agent.local's facts:

$ puppet lookup --node agent.local key_name

To get the first value found for key_name_one and key_name_two with agent.local's facts while merging values and knocking out the prefix 'example' while merging:

puppet lookup --node agent.local --merge deep --knock-out-prefix example key_name_one key_name_two

To lookup key_name with agent.local's facts, and return a default value of 0 if nothing is found:

puppet lookup --node agent.local --default 0 key_name

To see an explanation of how the value for key_name is found, using agent.local facts:

puppet lookup --node agent.local --explain key_name

The puppet lookup command has the following command options:

• --help: Print a usage message.

• --explain: Explain the details of how the lookup was performed and where the final value came from, or the reason no value was found. Useful when debugging Hiera data. If --explain isn't specified, lookup exits with 0 if a value was found and 1 if not. With --explain, lookup always exits with 0 unless there is a major error. You can provide multiple lookup keys to this command, but it only returns a value for the first found key, omitting the rest.

• --node <NODE-NAME>: Specify which node to look up data for; defaults to the node where the command is run. The purpose of Hiera is to provide different values for different nodes; use specific node facts to explore your data. If the node where you're running this command is configured to talk to PuppetDB, the command uses the requested node's most recent facts. Otherwise, override facts with the '--facts' option.

• --facts <FILE>: Specify a JSON or YAML file that contains key-value mappings to override the facts for this lookup. Any facts not specified in this file maintain their original value.

• --environment <ENV>: Specify an environment. Different environments can have different Hiera data.

• --merge first/unique/hash/deep: Specify the merge behavior, overriding any merge behavior from the data's lookup_options.

• --knock-out-prefix <PREFIX-STRING>: Used with 'deep' merge. Specifies a prefix to indicate a value should be removed from the final result.

• --sort-merged-arrays: Used with 'deep' merge. When this flag is used, all merged arrays are sorted.

• --merge-hash-arrays: Used with the 'deep' merge strategy. When this flag is used, hashes within arrays are deep-merged with their counterparts by position.

• --explain-options: Explain whether a lookup_options hash affects this lookup, and how that hash was assembled. (lookup_options is how Hiera configures merge behavior in data.)

• --default <VALUE>: A value to return if Hiera can't find a value in data. Useful for emulating a call to the `lookup function that includes a default.

• --type <TYPESTRING>: Assert that the value has the specified type. Useful for emulating a call to the lookup function that includes a data type.

• --compile: Perform a full catalog compilation prior to the lookup. If your hierarchy and data only use the $facts, $trusted, and $server_facts variables, you don't need this option. If your Hiera configuration uses arbitrary variables set by a Puppet manifest, you need this to get accurate data. The lookup command doesn't cause catalog compilation unless this flag is given.

• --render-as s/json/yaml/binary/msgpack: Specify the output format of the results; s means plain text. The default when producing a value is yaml and the default when producing an explanation is s.