ENV

ENV is a hash-like accessor for environment variables.

Interaction with the Operating System

The ENV object interacts with the operating system’s environment variables:

• When you get the value for a name in ENV, the value is retrieved from among the current environment variables.

• When you create or set a name-value pair in ENV, the name and value are immediately set in the environment variables.

• When you delete a name-value pair in ENV, it is immediately deleted from the environment variables.

Names and Values

Generally, a name or value is a String.

Valid Names and Values

Each name or value must be one of the following:

• A String.

• An object that responds to #to_str by returning a String, in which case that String will be used as the name or value.

Invalid Names and Values

A new name:

• May not be the empty string:

  Example

  Run in Playground

  ENV[''] = '0'
  # Raises Errno::EINVAL (Invalid argument - ruby_setenv())
  

• May not contain character "=":

  Example

  Run in Playground

  ENV['='] = '0'
  # Raises Errno::EINVAL (Invalid argument - ruby_setenv(=))
  

A new name or value:

• May not be a non-String that does not respond to #to_str:

  Example

  Run in Playground

  ENV['foo'] = Object.new
  # Raises TypeError (no implicit conversion of Object into String)
  ENV[Object.new] = '0'
  # Raises TypeError (no implicit conversion of Object into String)
  

• May not contain the NUL character "\0":

  Example

  Run in Playground

  ENV['foo'] = "\0"
  # Raises ArgumentError (bad environment variable value: contains null byte)
  ENV["\0"] == '0'
  # Raises ArgumentError (bad environment variable name: contains null byte)
  

• May not have an ASCII-incompatible encoding such as UTF-16LE or ISO-2022-JP:

  Example

  Run in Playground

  ENV['foo'] = '0'.force_encoding(Encoding::ISO_2022_JP)
  # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: ISO-2022-JP)
  ENV["foo".force_encoding(Encoding::ISO_2022_JP)] = '0'
  # Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: ISO-2022-JP)
  

About Ordering

ENV enumerates its name/value pairs in the order found in the operating system’s environment variables. Therefore the ordering of ENV content is OS-dependent, and may be indeterminate.

This will be seen in:

• A Hash returned by an ENV method.

• An Enumerator returned by an ENV method.

• An Array returned by ENV.keys, ENV.values, or ENV.to_a.

• The String returned by ENV.inspect.

• The Array returned by ENV.shift.

• The name returned by ENV.key.

About the Examples

Some methods in ENV return ENV itself. Typically, there are many environment variables. It’s not useful to display a large ENV in the examples here, so most example snippets begin by resetting the contents of ENV:

• ENV.replace replaces ENV with a new collection of entries.

• ENV.clear empties ENV.

What’s Here

First, what’s elsewhere. Class ENV:

• Inherits from class Object.

• Extends module Enumerable,

Here, class ENV provides methods that are useful for:

• Querying

• Assigning

• Deleting

• Iterating

• Converting

• And more .…

Methods for Querying

• ::[]: Returns the value for the given environment variable name if it exists:

• ::empty?: Returns whether ENV is empty.

• ::has_value?, ::value?: Returns whether the given value is in ENV.

• ::include?, ::has_key?, ::key?, ::member?: Returns whether the given name is in ENV.

• ::key: Returns the name of the first entry with the given value.

• ::size, ::length: Returns the number of entries.

• ::value?: Returns whether any entry has the given value.

Methods for Assigning

• ::[]=, ::store: Creates, updates, or deletes the named environment variable.

• ::clear: Removes every environment variable; returns ENV:

• ::update, ::merge!: Adds to ENV each key/value pair in the given hash.

• ::replace: Replaces the entire content of the ENV with the name/value pairs in the given hash.

Methods for Deleting

• ::delete: Deletes the named environment variable name if it exists.

• ::delete_if: Deletes entries selected by the block.

• ::keep_if: Deletes entries not selected by the block.

• ::reject!: Similar to delete_if, but returns nil if no change was made.

• ::select!, ::filter!: Deletes entries selected by the block.

• ::shift: Removes and returns the first entry.

Methods for Iterating

• ::each, ::each_pair: Calls the block with each name/value pair.

• ::each_key: Calls the block with each name.

• ::each_value: Calls the block with each value.

Methods for Converting

• ::assoc: Returns a 2-element array containing the name and value of the named environment variable if it exists:

• ::clone: Returns ENV (and issues a warning).

• ::except: Returns a hash of all name/value pairs except those given.

• ::fetch: Returns the value for the given name.

• ::inspect: Returns the contents of ENV as a string.

• ::invert: Returns a hash whose keys are the ENV values, and whose values are the corresponding ENV names.

• ::keys: Returns an array of all names.

• ::rassoc: Returns the name and value of the first found entry that has the given value.

• ::reject: Returns a hash of those entries not rejected by the block.

• ::select, ::filter: Returns a hash of name/value pairs selected by the block.

• ::slice: Returns a hash of the given names and their corresponding values.

• ::to_a: Returns the entries as an array of 2-element Arrays.

• ::to_h: Returns a hash of entries selected by the block.

• ::to_hash: Returns a hash of all entries.

• ::to_s: Returns the string 'ENV'.

• ::values: Returns all values as an array.

• ::values_at: Returns an array of the values for the given name.

More Methods

• ::dup: Raises an exception.

• ::freeze: Raises an exception.

• ::rehash: Returns nil, without modifying ENV.