We cover both methods of script execution in this book, with the bias towards web server usage. Most scripts will work smoothly in either environment, with the exception of scripts covered in the chapter "Alternative PHP uses", which require specific environments. You're encouraged to try using both when reading this book – it will give you more familiarity with how PHP works, and will also give you good experience using the CLI(Command Line Interface) SAPI(Server Application Programming Interface) to debug your scripts.

The primary difference between outputting text to the command line and to a web browser is the format of new lines – through the CLI you need to use n for a new line, whereas for web browsers you need to use the HTML line break, <BR />. If you want to take a script designed for CLI and make it work through the web, swap n for <BR />, and vice versa for converting web scripts to command line scripts.

Running scripts through your web server is as simple as putting the PHP script into your web server's public directory, then navigating to the appropriate URL with your browser. Hopefully you will already have followed the official PHP installation instructions for your platform!

Running scripts through the command line is done using the CLI SAPI, which, if you are using Windows, can be found in the CLI directory of your PHP installation. That is, if you have installed PHP into c:php, the CLI SAPI will be in c:phpcliphp.exe. If you are using Unix, the availability of the CLI SAPI is down to how you installed PHP - make sure and issue the command "make install-cli" after everything else in order to install it.

Later on we'll look at more detailed information on how using the CLI SAPI is different from normal PHP scripting, so don't rush off and try it out just yet!

If you are not sure about whether PHP is set up on your machine correctly, the best way forward is to run the following script:

<?php
   phpinfo();
?>

That calls a special function, phpinfo(), which outputs all the information PHP currently has – how it was configured, what server it is running on, what modules are available, and more. It is very handy to keep around when you are developing, as it will answer most questions you have about configuration.