PHPSAPI

PHPSAPI, short for PHP Server API, refers to the interface between PHP and its execution environment. It determines how PHP is loaded, executed, and interacts with the hosting context. The term is commonly used to describe the specific SAPI that governs a PHP process.

PHP supports multiple SAPIs, selected at build time or runtime. Common ones include CLI (command-line interface) for script execution and testing, Apache2handler or mod_php for integration with the Apache web server, CGI and FastCGI (including PHP-FPM) for dynamic web serving, and the embed SAPI used to embed PHP within another application. Each SAPI presents a different execution model and set of capabilities.

The SAPI influences available features, configuration, and environment. Web-server SAPIs typically provide request handling, server variables, and certain defaults for web contexts, while CLI offers interactive usage and scripting workflows. Many PHP settings, error handling behavior, and superglobal values may differ across SAPIs, and some features are only meaningful in a given SAPI.

To identify the active SAPI, use the PHP_SAPI constant or the php_sapi_name() function, and consult the output of phpinfo(), which lists the SAPI in its information section. This helps diagnose environment behavior, performance characteristics, and compatibility with server environments or tooling.

In PHP source and distribution, SAPIs are implemented under the sapi/ directory, with packaging often providing distinct binaries or modules for each SAPI. Deployment typically selects a SAPI by installing the appropriate PHP binary or server module and configuring the hosting environment accordingly.