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.

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.

    Example

    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:

    Example

    # 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:

    Example

    # 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:

    Example

    # 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.

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

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

Returns ENV itself, and warns because ENV is a wrapper for the process-wide environment variables and a clone is useless. If freeze keyword is given and not nil or false, raises ArgumentError. If freeze keyword is given and true, raises TypeError, as ENV storage cannot be frozen.

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

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

If a block is not given and the named environment variable does not exist, returns nil.

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

ENV.delete('foo') { |name| name * 2 } # => "foofoo"

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| raise 'ignored' } # => "0"

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

Yields each environment variable name and its value as a 2-element Array, deleting each environment variable for which the block returns a truthy value, and returning ENV (regardless of whether any deletions):

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

Returns an Enumerator if no block given:

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

Raises TypeError, because ENV is a singleton object. Use to_h to get a copy of ENV data as a hash.

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, false otherwise:

ENV.clear
ENV.empty? # => true
ENV['foo'] = '0'
ENV.empty? # => false

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

ENV                       #=> {"LANG"=>"en_US.UTF-8", "TERM"=>"xterm-256color", "HOME"=>"/Users/rhc"}
ENV.except("TERM","HOME") #=> {"LANG"=>"en_US.UTF-8"}

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.

ENV.filter is an alias for ENV.select.

Yields each environment variable name and its value as a 2-element Array, returning a Hash of the names and values for which the block returns a truthy value:

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

Returns an Enumerator if no block given:

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

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

Yields each environment variable name and its value as a 2-element Array, deleting each entry for which the block returns false or nil, and returning ENV if any deletions made, or nil otherwise:

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

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

Returns an Enumerator if no block given:

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

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

Raises an exception:

ENV.freeze # Raises TypeError (cannot freeze ENV)

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 value is the value for some environment variable name, false otherwise:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.value?('0') # => true
ENV.has_value?('0') # => true
ENV.value?('2') # => false
ENV.has_value?('2') # => false

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 the contents of the environment as a String:

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

Returns a Hash whose keys are the ENV values, and whose values are the corresponding ENV names:

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

For a duplicate ENV value, overwrites the hash entry:

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

Note that the order of the ENV processing is OS-dependent, which means that the order of overwriting is also OS-dependent. See About Ordering.

Yields each environment variable name and its value as a 2-element Array, deleting each environment variable for which the block returns false or nil, and returning ENV:

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

Returns an Enumerator if no block given:

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

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

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

Raises an exception if value is invalid:

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

See Invalid Names and Values.

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.

Returns the count of environment variables:

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

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)

ENV.update is an alias for ENV.merge!.

Adds to ENV each key/value pair in the given hash; returns ENV:

ENV.replace('foo' => '0', 'bar' => '1')
ENV.merge!('baz' => '2', 'bat' => '3') # => {"bar"=>"1", "bat"=>"3", "baz"=>"2", "foo"=>"0"}

Deletes the ENV entry for a hash value that is nil:

ENV.merge!('baz' => nil, 'bat' => nil) # => {"bar"=>"1", "foo"=>"0"}

For an already-existing name, if no block given, overwrites the ENV value:

ENV.merge!('foo' => '4') # => {"bar"=>"1", "foo"=>"4"}

For an already-existing name, if block given, yields the name, its ENV value, and its hash value; the block’s return value becomes the new name:

ENV.merge!('foo' => '5') { |name, env_val, hash_val | env_val + hash_val } # => {"bar"=>"1", "foo"=>"45"}

Raises an exception if a name or value is invalid (see Invalid Names and Values);

ENV.replace('foo' => '0', 'bar' => '1')
ENV.merge!('foo' => '6', :bar => '7', 'baz' => '9') # Raises TypeError (no implicit conversion of Symbol into String)
ENV # => {"bar"=>"1", "foo"=>"6"}
ENV.merge!('foo' => '7', 'bar' => 8, 'baz' => '9') # Raises TypeError (no implicit conversion of Integer into String)
ENV # => {"bar"=>"1", "foo"=>"7"}

Raises an exception if the block returns an invalid name: (see Invalid Names and Values):

ENV.merge!('bat' => '8', 'foo' => '9') { |name, env_val, hash_val | 10 } # Raises TypeError (no implicit conversion of Integer into String)
ENV # => {"bar"=>"1", "bat"=>"8", "foo"=>"7"}

Note that for the exceptions above, hash pairs preceding an invalid name or value are processed normally; those following are ignored.

Returns a 2-element Array containing the name and value of the first found environment variable that has value value, if one exists:

ENV.replace('foo' => '0', 'bar' => '0')
ENV.rassoc('0') # => ["bar", "0"]

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

Returns nil if there is no such environment variable.

(Provided for compatibility with Hash.)

Does not modify ENV; returns nil.

Yields each environment variable name and its value as a 2-element Array. Returns a Hash whose items are determined by the block. When the block returns a truthy value, the name/value pair is added to the return Hash; otherwise the pair is ignored:

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

Returns an Enumerator if no block given:

e = ENV.reject
e.each { |name, value| name.start_with?('b') } # => {"foo"=>"0"}

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

Yields each environment variable name and its value as a 2-element Array, deleting each environment variable for which the block returns a truthy value, and 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):

ENV.replace('foo' => '0', :bar => '1') # Raises TypeError (no implicit conversion of Symbol into String)
ENV.replace('foo' => '0', 'bar' => 1) # Raises TypeError (no implicit conversion of Integer into String)
ENV.to_hash # => {"bar"=>"1", "foo"=>"0"}

ENV.filter is an alias for ENV.select.

Yields each environment variable name and its value as a 2-element Array, returning a Hash of the names and values for which the block returns a truthy value:

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

Returns an Enumerator if no block given:

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

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

Yields each environment variable name and its value as a 2-element Array, deleting each entry for which the block returns false or nil, and returning ENV if any deletions made, or nil otherwise:

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

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

Returns an Enumerator if no block given:

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

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

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.

Returns the count of environment variables:

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

Returns a Hash of the given ENV names and their corresponding values:

ENV.replace('foo' => '0', 'bar' => '1', 'baz' => '2', 'bat' => '3')
ENV.slice('foo', 'baz') # => {"foo"=>"0", "baz"=>"2"}
ENV.slice('baz', 'foo') # => {"baz"=>"2", "foo"=>"0"}

Raises an exception if any of the names is invalid (see Invalid Names and Values):

ENV.slice('foo', 'bar', :bat) # Raises TypeError (no implicit conversion of Symbol into String)

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.

    Example

    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:

    Example

    # 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:

    Example

    # 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:

    Example

    # 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