What is environment?

sebastian/environment is a small PHP utility library that makes it easier to write code with different behavior depending on which runtime is executing it. PHP programs can run on standard PHP (the official interpreter) or on HHVM, an alternative runtime originally developed by Meta that implements PHP with a just-in-time compiler. The two runtimes can differ in subtle ways, and this library provides a way to detect the current environment so developers can write code that adapts its execution path accordingly. The practical use case is often in test frameworks or developer tools, where behavior differences between runtimes need to be handled explicitly. Rather than scattering inline checks throughout application code, centralizing runtime detection behind a small library keeps that logic reusable and easier to test. Installation is through Composer, the standard package manager for PHP. You can add it as a regular dependency if your production code needs it, or restrict it to development use if you only need it when running a test suite. The command is composer require sebastian/environment or, for development-only installation, composer require --dev sebastian/environment. The README for this repository is minimal: it states the purpose in one sentence and provides the install command. No usage examples, API reference, or list of available detection methods appears in the file, so the full capabilities of the library are not detailed here.