How do environment variables work?

Environment variables work as key-value pairs that are stored in the operating system's environment. Here's how they function:

1. Setting Variables: You can set an environment variable using commands like export in Linux. For example:

   export MY_VAR="Hello, World!"
   

2. Accessing Variables: Once set, you can access the value of an environment variable using commands like echo:

   echo $MY_VAR
   

3. Scope: Environment variables can be local to a session or global. Local variables are available only in the current shell session, while global variables can be made persistent by adding them to shell configuration files (e.g., .bashrc, .zshrc).

4. Using in Programs: Programs can access these variables using system calls or libraries. For example, in Go, you can use os.Getenv to retrieve the value of an environment variable:

   value := os.Getenv("MY_VAR")
   

5. Listing Variables: You can list all environment variables using the env command or by accessing them programmatically (e.g., os.Environ() in Go).

Environment variables are essential for configuring applications and managing system settings dynamically.