Class

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:

    ENV[''] = '0'
    # Raises Errno::EINVAL (Invalid argument - ruby_setenv())
    
  • May not contain character "=":

    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:

    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":

    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:

    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:

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:


Returns the value for the environment variable name if it exists:

ENV['foo'] = '0'
ENV['foo'] # => "0"

Returns nil if the named variable does not exist:

ENV.clear
ENV['foo'] # => nil

Raises an exception if name is invalid. See Invalid Names and Values.

ENV.store is an alias for ENV.[]=.

Creates, updates, or deletes the named environment variable, returning the value. Both name and value may be instances of String. See Valid Names and Values.

  • If the named environment variable does not exist:

    • If value is nil, does nothing.

      ENV.clear
      ENV['foo'] = nil # => nil
      ENV.include?('foo') # => false
      ENV.store('bar', nil) # => nil
      ENV.include?('bar') # => false
      
    • If value is not nil, creates the environment variable with name and value:

      # Create 'foo' using ENV.[]=.
      ENV['foo'] = '0' # => '0'
      ENV['foo'] # => '0'
      # Create 'bar' using ENV.store.
      ENV.store('bar', '1') # => '1'
      ENV['bar'] # => '1'
      
  • If the named environment variable exists:

    • If value is not nil, updates the environment variable with value value:

      # Update 'foo' using ENV.[]=.
      ENV['foo'] = '2' # => '2'
      ENV['foo'] # => '2'
      # Update 'bar' using ENV.store.
      ENV.store('bar', '3') # => '3'
      ENV['bar'] # => '3'
      
    • If value is nil, deletes the environment variable:

      # Delete 'foo' using ENV.[]=.
      ENV['foo'] = nil # => nil
      ENV.include?('foo') # => false
      # Delete 'bar' using ENV.store.
      ENV.store('bar', nil) # => nil
      ENV.include?('bar') # => false
      

Raises an exception if name or value is invalid. See Invalid Names and Values.

Returns a 2-element Array containing the name and value of the environment variable for name if it exists:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.assoc('foo') # => ['foo' '0']

Returns nil if name is a valid String and there is no such environment variable:

ENV.assoc('baz') # => false

Returns nil if name is the empty String or is a String containing character '=':

ENV.assoc('') # => false
ENV.assoc('=') # => false

Raises an exception if name is a String containing the NUL character "\0":

ENV.assoc("\0") # Raises ArgumentError (bad environment variable name: contains null byte)

Raises an exception if name has an encoding that is not ASCII-compatible:

ENV.assoc("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
# Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)

Raises an exception if name is not a String:

ENV.assoc(Object.new) # TypeError (no implicit conversion of Object into String)

Removes every environment variable; returns ENV:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.size # => 2
ENV.clear # => ENV
ENV.size # => 0

Deletes the environment variable with name if it exists and returns its value:

ENV['foo'] = '0'
ENV.delete('foo') # => '0'

Returns nil if the named environment variable does not exist:

ENV.delete('foo') # => nil

If a block given and the environment variable does not exist, yields name to the block and returns nil:

ENV.delete('foo') { |name| puts name } # => nil
foo

If a block given and the environment variable exists, deletes the environment variable and returns its value (ignoring the block):

ENV['foo'] = '0'
ENV.delete('foo') { |name| fail 'ignored' } # => "0"

Raises an exception if name is invalid. See Invalid Names and Values.

Deletes every environment variable for which the block evaluates to true.

If no block is given an enumerator is returned instead.

Yields each environment variable name and its value as a 2-element Array:

h = {}
ENV.each_pair { |name, value| h[name] = value } # => ENV
h # => {"bar"=>"1", "foo"=>"0"}

Returns an Enumerator if no block given:

h = {}
e = ENV.each_pair # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_pair>
e.each { |name, value| h[name] = value } # => ENV
h # => {"bar"=>"1", "foo"=>"0"}

Yields each environment variable name:

ENV.replace('foo' => '0', 'bar' => '1') # => ENV
names = []
ENV.each_key { |name| names.push(name) } # => ENV
names # => ["bar", "foo"]

Returns an Enumerator if no block given:

e = ENV.each_key # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_key>
names = []
e.each { |name| names.push(name) } # => ENV
names # => ["bar", "foo"]

Yields each environment variable name and its value as a 2-element Array:

h = {}
ENV.each_pair { |name, value| h[name] = value } # => ENV
h # => {"bar"=>"1", "foo"=>"0"}

Returns an Enumerator if no block given:

h = {}
e = ENV.each_pair # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_pair>
e.each { |name, value| h[name] = value } # => ENV
h # => {"bar"=>"1", "foo"=>"0"}

Yields each environment variable value:

ENV.replace('foo' => '0', 'bar' => '1') # => ENV
values = []
ENV.each_value { |value| values.push(value) } # => ENV
values # => ["1", "0"]

Returns an Enumerator if no block given:

e = ENV.each_value # => #<Enumerator: {"bar"=>"1", "foo"=>"0"}:each_value>
values = []
e.each { |value| values.push(value) } # => ENV
values # => ["1", "0"]

Returns true when there are no environment variables

If name is the name of an environment variable, returns its value:

ENV['foo'] = '0'
ENV.fetch('foo') # => '0'

Otherwise if a block is given (but not a default value), yields name to the block and returns the block's return value:

ENV.fetch('foo') { |name| :need_not_return_a_string } # => :need_not_return_a_string

Otherwise if a default value is given (but not a block), returns the default value:

ENV.delete('foo')
ENV.fetch('foo', :default_need_not_be_a_string) # => :default_need_not_be_a_string

If the environment variable does not exist and both default and block are given, issues a warning (“warning: block supersedes default value argument”), yields name to the block, and returns the block's return value:

ENV.fetch('foo', :default) { |name| :block_return } # => :block_return

Raises KeyError if name is valid, but not found, and neither default value nor block is given:

ENV.fetch('foo') # Raises KeyError (key not found: "foo")

Raises an exception if name is invalid. See Invalid Names and Values.

Returns a copy of the environment for entries where the block returns true.

Returns an Enumerator if no block was given.

ENV.filter is an alias for ENV.select.

Equivalent to ENV.keep_if but returns nil if no changes were made.

ENV.filter! is an alias for ENV.select!.

Ruby does not allow ENV to be frozen, so calling ENV.freeze raises TypeError.

ENV.has_key?, ENV.member?, and ENV.key? are aliases for ENV.include?.

Returns true if there is an environment variable with the given name:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.include?('foo') # => true

Returns false if name is a valid String and there is no such environment variable:

ENV.include?('baz') # => false

Returns false if name is the empty String or is a String containing character '=':

ENV.include?('') # => false
ENV.include?('=') # => false

Raises an exception if name is a String containing the NUL character "\0":

ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)

Raises an exception if name has an encoding that is not ASCII-compatible:

ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
# Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)

Raises an exception if name is not a String:

ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)

Returns true if there is an environment variable with the given value.

ENV.has_key?, ENV.member?, and ENV.key? are aliases for ENV.include?.

Returns true if there is an environment variable with the given name:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.include?('foo') # => true

Returns false if name is a valid String and there is no such environment variable:

ENV.include?('baz') # => false

Returns false if name is the empty String or is a String containing character '=':

ENV.include?('') # => false
ENV.include?('=') # => false

Raises an exception if name is a String containing the NUL character "\0":

ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)

Raises an exception if name has an encoding that is not ASCII-compatible:

ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
# Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)

Raises an exception if name is not a String:

ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)

Deprecated method that is equivalent to ENV.key

Returns the contents of the environment as a String.

Returns a new hash created by using environment variable names as values and values as names.

Deletes every environment variable where the block evaluates to false.

Returns an enumerator if no block was given.

Returns the name of the first environment variable with value if it exists:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.key('0') # =>'foo'

The order in which environment variables are examined is OS-dependent. See About Ordering.

Returns nil if there is no such value:

ENV.key('2') # => nil

Raises an exception if value is not a String:

ENV.key(Object.new) # raises TypeError (no implicit conversion of Object into String)

ENV.has_key?, ENV.member?, and ENV.key? are aliases for ENV.include?.

Returns true if there is an environment variable with the given name:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.include?('foo') # => true

Returns false if name is a valid String and there is no such environment variable:

ENV.include?('baz') # => false

Returns false if name is the empty String or is a String containing character '=':

ENV.include?('') # => false
ENV.include?('=') # => false

Raises an exception if name is a String containing the NUL character "\0":

ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)

Raises an exception if name has an encoding that is not ASCII-compatible:

ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
# Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)

Raises an exception if name is not a String:

ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)

Returns all variable names in an Array:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.keys # => ['bar', 'foo']

The order of the names is OS-dependent. See About Ordering.

Returns the empty Array if ENV is empty:

ENV.clear
ENV.keys # => []

Returns the number of environment variables.

ENV.has_key?, ENV.member?, and ENV.key? are aliases for ENV.include?.

Returns true if there is an environment variable with the given name:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.include?('foo') # => true

Returns false if name is a valid String and there is no such environment variable:

ENV.include?('baz') # => false

Returns false if name is the empty String or is a String containing character '=':

ENV.include?('') # => false
ENV.include?('=') # => false

Raises an exception if name is a String containing the NUL character "\0":

ENV.include?("\0") # Raises ArgumentError (bad environment variable name: contains null byte)

Raises an exception if name has an encoding that is not ASCII-compatible:

ENV.include?("\xa1\xa1".force_encoding(Encoding::UTF_16LE))
# Raises ArgumentError (bad environment variable name: ASCII incompatible encoding: UTF-16LE)

Raises an exception if name is not a String:

ENV.include?(Object.new) # TypeError (no implicit conversion of Object into String)

Adds the contents of hash to the environment variables. If no block is specified entries with duplicate keys are overwritten, otherwise the value of each duplicate name is determined by calling the block with the key, its value from the environment and its value from the hash.

Returns an Array of the name and value of the environment variable with value or nil if the value cannot be found.

Re-hashing the environment variables does nothing. It is provided for compatibility with Hash.

Same as ENV.delete_if, but works on (and returns) a copy of the environment.

Similar to ENV.delete_if, but returns nil if no changes were made.

Deletes each environment variable for which the block returns a truthy value, returning ENV (if any deletions) or nil (if not):

ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
ENV.reject! { |name, value| name.start_with?('b') } # => ENV
ENV # => {"foo"=>"0"}
ENV.reject! { |name, value| name.start_with?('b') } # => nil

Returns an Enumerator if no block given:

ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2')
e = ENV.reject! # => #<Enumerator: {"bar"=>"1", "baz"=>"2", "foo"=>"0"}:reject!>
e.each { |name, value| name.start_with?('b') } # => ENV
ENV # => {"foo"=>"0"}
e.each { |name, value| name.start_with?('b') } # => nil

Replaces the entire content of the environment variables with the name/value pairs in the given hash; returns ENV.

Replaces the content of ENV with the given pairs:

ENV.replace('foo' => '0', 'bar' => '1') # => ENV
ENV.to_hash # => {"bar"=>"1", "foo"=>"0"}

Raises an exception if a name or value is invalid. See Invalid Names and Values.

Returns a copy of the environment for entries where the block returns true.

Returns an Enumerator if no block was given.

ENV.filter is an alias for ENV.select.

Equivalent to ENV.keep_if but returns nil if no changes were made.

ENV.filter! is an alias for ENV.select!.

Removes the first environment variable from ENV and returns a 2-element Array containing its name and value:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.to_hash # => {'bar' => '1', 'foo' => '0'}
ENV.shift # => ['bar', '1']
ENV.to_hash # => {'foo' => '0'}

Exactly which environment variable is “first” is OS-dependent. See About Ordering.

Returns nil if the environment is empty:

ENV.clear
ENV.shift # => nil

Returns the number of environment variables.

Returns a hash containing only the given keys from ENV and their values.

ENV.slice("TERM","HOME")  #=> {"TERM"=>"xterm-256color", "HOME"=>"/Users/rhc"}

ENV.store is an alias for ENV.[]=.

Creates, updates, or deletes the named environment variable, returning the value. Both name and value may be instances of String. See Valid Names and Values.

  • If the named environment variable does not exist:

    • If value is nil, does nothing.

      ENV.clear
      ENV['foo'] = nil # => nil
      ENV.include?('foo') # => false
      ENV.store('bar', nil) # => nil
      ENV.include?('bar') # => false
      
    • If value is not nil, creates the environment variable with name and value:

      # Create 'foo' using ENV.[]=.
      ENV['foo'] = '0' # => '0'
      ENV['foo'] # => '0'
      # Create 'bar' using ENV.store.
      ENV.store('bar', '1') # => '1'
      ENV['bar'] # => '1'
      
  • If the named environment variable exists:

    • If value is not nil, updates the environment variable with value value:

      # Update 'foo' using ENV.[]=.
      ENV['foo'] = '2' # => '2'
      ENV['foo'] # => '2'
      # Update 'bar' using ENV.store.
      ENV.store('bar', '3') # => '3'
      ENV['bar'] # => '3'
      
    • If value is nil, deletes the environment variable:

      # Delete 'foo' using ENV.[]=.
      ENV['foo'] = nil # => nil
      ENV.include?('foo') # => false
      # Delete 'bar' using ENV.store.
      ENV.store('bar', nil) # => nil
      ENV.include?('bar') # => false
      

Raises an exception if name or value is invalid. See Invalid Names and Values.

Converts the environment variables into an array of names and value arrays.

ENV.to_a # => [["TERM", "xterm-color"], ["SHELL", "/bin/bash"], ...]

Creates a hash with a copy of the environment variables.

Creates a hash with a copy of the environment variables.

Returns “ENV”

Adds the contents of hash to the environment variables. If no block is specified entries with duplicate keys are overwritten, otherwise the value of each duplicate name is determined by calling the block with the key, its value from the environment and its value from the hash.

Returns true if there is an environment variable with the given value.

Returns all environment variable values in an Array:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.values # => ['1', '0']

The order of the values is OS-dependent. See About Ordering.

Returns the empty Array if ENV is empty:

ENV.clear
ENV.values # => []

Returns an array containing the environment variable values associated with the given names. See also ENV.select.