How PHP Scripts Execute: A Detailed Look at Parsing, Compilation, and Execution

Unraveling the Execution Process of PHP Scripts

Often wondered about the intricate workings of PHP script execution? While many intuit a process of parsing for errors followed by interpretation and execution, let's delve deeper into the precise stages involved.

The Evolution of PHP: From Interpretation to Compilation

Prior to PHP 4.0, PHP scripts were interpreted, meaning their source code was directly executed by the interpreter. However, PHP's trajectory changed dramatically with the introduction of PHP 4.0 in 2000.

The Zend Engine: A Two-Phase Orchestrator

PHP 4.0 ushered in the Zend engine, a revolutionary component that transformed PHP into a compiled language. The Zend engine orchestrates the execution process in two distinct phases:

Phase 1: Parsing and Code Generation

In this phase, the PHP source code is meticulously parsed, generating a binary representation known as Zend opcodes. These opcodes encapsulate a set of instructions akin to Java bytecodes and are subsequently stored in memory.

Phase 2: Opcode Execution

Armed with the generated opcodes, the Zend engine embarks on the second phase of execution. It meticulously executes the opcodes, translating them into the desired output.

Parsing Included Files

Included files play a crucial role in PHP script execution. They are incorporated into the script's scope, having their own parser and execution phases. The Zend engine seamlessly stitches these included files into the main script, ensuring their code is seamlessly integrated and executed.

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