當(dāng)用戶請求PHP文件時(shí)，服務(wù)器通過Apache或Nginx調(diào)用PHP解釋器執(zhí)行腳本並返迴響應(yīng)。具體流程如下：1. 用戶發(fā)起HTTP請求，服務(wù)器識別.php文件並將請求傳遞給PHP處理；2. PHP啟動時(shí)加載擴(kuò)展、設(shè)置環(huán)境變量並初始化函數(shù)；3. 執(zhí)行腳本代碼，包括解析文件、調(diào)用函數(shù)、數(shù)據(jù)庫查詢及輸出緩衝；4. 腳本執(zhí)行完畢後，PHP將頭部信息和響應(yīng)內(nèi)容髮送回服務(wù)器，再傳輸至用戶瀏覽器，隨後清理資源完成響應(yīng)。

Sure! Let's walk through how a PHP script actually runs from the moment someone makes a request to when they get a response.

1. The Request Comes In

When a user types a URL into their browser or clicks a link, their browser sends an HTTP request to the server. If that request is for a .php file (like index.php ), the web server (Apache, Nginx, etc.) knows it needs to involve PHP.

• For Apache, it usually uses mod_php or FastCGI
• For Nginx, it typically passes the request to PHP-FPM

At this point, the web server parses the URL and maps it to a physical file on the server — like /var/www/html/index.php .

2. PHP Starts Up

Once the server decides to run PHP, it starts up the PHP interpreter. This is where things like:

• Loading extensions ( mysqli , json , etc.)
• Setting up environment variables
• Initializing built-in functions and global settings

happen behind the scenes before your actual script even begins to run.

It's worth noting: if you're using opcache, PHP might skip re-parsing and re-compiling the script if it's already been compiled recently.

3. Your Script Runs

Now comes the part you're most familiar with — your PHP code gets executed line by line.

Let's say you have something like:

 <?php
// index.php
require &#39;config.php&#39;;
$data = fetch_from_database();
echo json_encode($data);

In this phase:

• PHP reads the file (or uses cached bytecode if available)
• It parses and compiles the script into opcodes
• Then executes those opcodes
• Any output (like from echo ) gets buffered

Also during execution:

• Any included or required files are loaded
• Functions are called
• Database queries may be made
• Sessions might be started
• Headers could be sent (using header() )

This is also where errors or notices might show up, depending on your error reporting settings.

4. Output Gets Sent Back

After your script finishes running, PHP flushes any buffered output and sends it back to the web server, which then sends it to the browser.

Headers go first — things like content type ( text/html , application/json ), cookies, redirects, etc.

Then comes the body — whatever was echoed or printed in your script.

Once all that is done, PHP shuts down, cleaning up memory, closing connections, and releasing resources.

If you're using persistent database connections or something like Redis, those might stay open briefly, but PHP tries to tidy up as best as it can unless told otherwise.

That's basically it. From request to response, PHP does a lot quietly so you can focus on writing your logic.

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