Class: ENV

Inherits:
Object show all
Defined in:
hash.c

Overview

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:

  • 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.