There are key differences between CLI PHP and Web PHP in configuration files, execution environments, error handling and usage scenarios. 1. Different configuration files, CLI usually uses /etc/php/8.x/cli/php.ini, while Web PHP uses such as /etc/php/8.x/apache2/php.ini, resulting in inconsistent settings such as display_errors; 2. Different execution environments, CLI runs on end users, and Web PHP runs on web server users (such as www-data), affecting permissions, environment variables and input and output methods; 3. Different error handling methods, CLI displays detailed error information by default, and Web PHP may record errors in logs rather than displaying them in the browser; 4. Different usage scenarios, CLI is suitable for command-line tasks such as timed jobs and unit tests, and Web PHP is used to handle HTTP requests and service dynamic content.

When you're working with PHP, it's easy to assume that the language behaves the same whether you're running it from the command line or through a web server. But in practice, CLI PHP and Web PHP have some important differences that can affect how scripts behave, what configurations are active, and even how errors are handled.

Let's break down the key distinctions so you know what to expect when switching between environments.

Configuration Files Can Be Different

One of the first things you might notice is that CLI PHP often uses a different php.ini file than Web PHP.

• When you run PHP from the terminal using php , it typically loads a configuration file like /etc/php/8.x/cli/php.ini .
• When PHP runs via Apache or Nginx, it usually uses something like /etc/php/8.x/apache2/php.ini or /etc/php/8.x/fpm/php.ini .

This means settings like display_errors , error_reporting , or memory_limit might be set differently depending on which environment you're in.

? A common gotcha: You might not see errors displayed in the browser because display_errors is turned off in the web version, but it's enabled in the CLI version, so they show up in your terminal.

You can check which config file is being used by running:

 php --ini # for CLI

And in a script accessed through the web:

 <?php phpinfo();

Execution Context and Environment Variables Vary

CLI PHP runs in a shell environment, while Web PHP runs under the web server user (like www-data ).

This affects:

• File system permissions — scripts may have different access to files and directories.
• Environment variables — some variables available in the shell aren't present in the web context and vice versa.
• User interaction — CLI scripts can read input from the terminal ( fgets(STDIN) ), while web scripts rely on HTTP requests.

For example, if you're writing a script that needs to read user input or output progress bars, those features only make sense in the CLI world.

Also, paths can behave differently. Relative paths in web scripts are relative to the document root or current script path, while in CLI, they're relative to where you're running the script from.

Error Handling and Output Are Treated Differently

Error handling in CLI and Web PHP can lead to different behaviors, especially during debugging.

In CLI :

• Errors and notices are usually printed directly to the terminal.
• The default error reporting level tends to be more verbose.

In Web PHP :

• Errors might be logged to a file instead of shown in the browser.
• Settings like display_errors and log_errors determine what happens.

So if a script works fine in the terminal but shows a blank page in the browser, it's likely due to an error that's being suppressed or logged elsewhere.

? Tip: Always check the web server's error log if something isn't behaving as expected. In many settings, it'll be something like /var/log/apache2/error.log or /var/log/nginx/error.log .

Performance and Use Cases Aren't the Same

CLI PHP is great for tasks that don't involve HTTP requests:

• Cron jobs
• Data imports/exports
• Long-running processes
• Unit tests

Web PHP, on the other hand, handles:

• HTTP requests
• Serving dynamic content
• Managing sessions and cookies

Because CLI scripts don't go through the overhead of a web request, they can sometimes perform better for background processing.

Also, timeouts work differently. Web scripts often have a time limit (like 30 seconds by default), while CLI scripts can run indefinitely unless explicitly configured otherwise.

Basically that's it. The difference between CLI and Web PHP seems to be small, but in actual development and debugging, it often brings confusion about "why can't you run in this environment in that environment". Understanding the differences between them can help you troubleshoot problems more efficiently and make more appropriate design choices when writing scripts.

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