Ruby Environment Variables

Environment variables are a set of dynamic named values that can affect the way running processes behave on a computer. In Ruby, the ENV object is used to interact with the environment variables.

Here is a brief tutorial on how to use environment variables in Ruby:

1. Accessing Environment Variables:

To access an environment variable, you use ENV followed by the name of the variable in square brackets. For example, to get the value of the PATH environment variable:

puts ENV['PATH']

2. Setting Environment Variables:

You can also set the value of an environment variable using ENV. This will only affect the environment variable for the currently running process and any processes it spawns - it won't change the variable globally on your system or affect other running processes. For example:

ENV['MY_VARIABLE'] = 'my value'
puts ENV['MY_VARIABLE'] # Outputs: my value

3. Deleting Environment Variables:

You can delete an environment variable from the environment of the current process using the delete method:

ENV['MY_VARIABLE'] = 'my value'
ENV.delete('MY_VARIABLE')
puts ENV['MY_VARIABLE'] # Outputs: nil

4. Iterating Over Environment Variables:

You can iterate over all environment variables and their values using each:

ENV.each do |key, value|
  puts "#{key}: #{value}"
end

5. Checking if an Environment Variable Exists:

You can check if an environment variable exists using the has_key? method or include? method:

if ENV.has_key?('PATH')
  puts "PATH exists"
end

if ENV.include?('PATH')
  puts "PATH exists"
end

Remember, changes made to environment variables within a Ruby program only affect the current process and any subprocesses it spawns. They don't persist after the program exits, and they don't affect other running processes.

In addition, you should be careful not to expose sensitive data such as passwords, API keys, or other secrets in your environment variables, especially if you're working in a shared or public environment. It's usually a good idea to keep these values in a secure, encrypted storage and only read them into your program's environment when necessary.

Setting and accessing environment variables in Ruby:
- Description: Use the ENV hash to set and access environment variables in Ruby.
- Code example:
```
# Setting an environment variable
ENV['MY_VARIABLE'] = 'my_value'

# Accessing an environment variable
puts ENV['MY_VARIABLE']
```
Ruby ENV class:
- Description: The ENV class in Ruby provides a hash-like interface for accessing environment variables.
- Code example:
```
# Accessing environment variables using ENV class
puts ENV['PATH']
```

How to export environment variables in Ruby:

Description: Environment variables can be exported in the terminal or set within a Ruby script.

Code example:

# Exporting environment variables in the terminal
export MY_VARIABLE=my_value

# Setting environment variables within a Ruby script
ENV['MY_VARIABLE'] = 'my_value'

Environment variable substitution in Ruby:
- Description: Use environment variable substitution to include variable values in strings.
- Code example:
```
# Substituting environment variable in a string
puts "My variable value: #{ENV['MY_VARIABLE']}"
```
Reading environment variables in a Ruby script:
- Description: Read and use environment variables within a Ruby script for configuration.
- Code example:
```
# Reading and using environment variable in a script
api_key = ENV['API_KEY']
puts "API Key: #{api_key}"
```
Ruby dotenv gem usage:
- Description: The dotenv gem simplifies the management of environment variables by loading them from a .env file.
- Code example:
```
# Gemfile
gem 'dotenv', '~> 2.7'

# .env file
API_KEY=my_api_key

# Ruby script
require 'dotenv/load'
puts "API Key: #{ENV['API_KEY']}"
```