environmentVariables

Environment variables are dynamic named values used by an operating system and runtimes to configure the behavior of running processes. They are stored as key-value pairs and are provided to processes when they start. Each process has its own environment, typically inherited from its parent, and can read these values to determine settings such as file paths, locale, and runtime options.

Scope and lifecycle vary by platform. Environment variables can be set at the session level in a shell, per-user in the operating system, or system-wide for all users. Changes in a shell typically affect only the current session or its offspring, unless made persistent through startup files or system configuration.

Common examples include PATH (directories searched for executables), HOME or USERPROFILE (user home directory), LANG or LC_* (locale settings), and TEMP or TMP (temporary file location). Windows uses variables like PROGRAMFILES and APPDATA in addition to PATH, while Unix-like systems rely on PATH, LD_LIBRARY_PATH, and HOME.

Access and manipulation span many languages. In shells, variables are created or exported (export VAR=value); in Windows, set VAR=value or set VAR=value and then child processes inherit it. In programming languages, environments are read via APIs such as Python’s os.environ, Java’s System.getenv, or Node.js’s process.env.

Security and reliability considerations are important. Environment variables can expose secrets if misused, and they may be inherited unexpectedly. Avoid storing sensitive data in environment variables in shared contexts; prefer dedicated secret management and clear variables when no longer needed.

Best practices include documenting variable names, providing sensible defaults, and minimizing dependency on environment state for core logic, while using environment configuration for deployment-time customization.