org.apache.commons.configuration2.interpol

## Class EnvironmentLookup

- java.lang.Object
- - org.apache.commons.configuration2.interpol.EnvironmentLookup

- All Implemented Interfaces:
    Lookup

      public class EnvironmentLookup
      extends Object
      implements Lookup

  A specialized lookup implementation that allows access to environment variables.

  This implementation relies on `System.getenv()` to resolve environment variables. It can be used for referencing environment variables in configuration files in an easy way, for instance:

       java.home = ${env:JAVA_HOME}

  `EnvironmentLookup` is one of the standard lookups that is registered per default for each configuration.

  Since:
    1.7
  Version:
    $Id: EnvironmentLookup.java 1679784 2015-05-16 17:46:21Z oheger $
  Author:
    Commons Configuration team

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `EnvironmentLookup()`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `String` | `lookup(String key)` Performs a lookup for the specified variable.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### EnvironmentLookup

          public EnvironmentLookup()

  - ### Method Detail

    - #### lookup

          public String lookup(String key)

      Performs a lookup for the specified variable. This implementation directly delegates to a `System.getenv()`.
      Specified by:
        `lookup` in interface `Lookup`
      Parameters:
        `key` - the key to lookup
      Returns:
        the value of this key or null if it cannot be resolved

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