


Could you detail the lifecycle of a PHP script from request to response?
Jun 05, 2025 am 12:10 AMWhen the user requests a PHP file, the server calls the PHP interpreter through Apache or Nginx to execute the script and returns the response. The specific process is as follows: 1. The user initiates an HTTP request, the server recognizes the .php file and passes the request to PHP for processing; 2. Loads the extension, sets environment variables and initializes the functions when PHP starts; 3. Execute script code, including parsing files, calling functions, database query and output buffering; 4. After the script is executed, PHP sends the header information and response content back to the server, then transmits it to the user's browser, and then cleans up the resources to complete the response.
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 'config.php'; $data = fetch_from_database(); echo json_encode($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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