There are two options.

1. Access the php file through a local webserver(ie thru a local website). The web-server will deal with the requested php file. It will use either,

   • Inbuilt PHP module to interpret the php file, or

   • PHP through CGI (eg.CGI, FastCGI)
     
     If your apache(check if apache is running using service apache2 status!!) is set to the default configuration, this could be as simple as
     

     http://localhost/path/to/your.php
     

     Remember by default, the base directory for apache is /var/www/html/, so you need not include this in the url.

2. Use the php binary directly from a terminal.

      php /path/to/your/file.php
   

To open an interactive php shell, just type in a terminal:

php -a

As for opening a file, just:

php filename.php

Make sure you have LAMP installed. Do a sudo tasksel and select lamp then hit enter, its gotta be the most simple *amp install ever made. Its a good idea to install phpmyadmin: sudo apt-get install phpmyadmin. After that just copy the files to /var/www/ and then they will show up on http://localhost. I recommended using Eclipse PDT or the Netbeans build for PHP.

This answer provides details on LAMP and PHP Install. This answer provides the details on "how to run php" on your web server.

In this answer you'll get the steps on how to install MySQL. But the details on how to connect php into mysql are too long and probably off topic right here. So I suggest you to first meet the requirements to properly run LAMP.

Additionally you may wish to have a look at this post on howtoforge, of which I place here the relevant things for your convenience:

Installing LAMP On Ubuntu For Newbies

In this guide I will show you how to install a LAMP system. LAMP stands for Linux, Apache, MySQL, PHP. The guide is intended to help those who have very little knowlegde of using Linux.

Install Apache

To start off we will install Apache.

1. Open up the Terminal (Applications > Accessories > Terminal). (Ctrl+T also works)

2. Copy/Paste the following line of code into Terminal and then press enter:

   sudo apt-get install apache2

3. The Terminal will then ask you for you're password, type it and then press enter.

Testing Apache

To make sure everything installed correctly we will now test Apache to ensure it is working properly.

1. Open up any web browser and then enter the following into the web address:

http://localhost/

You should see a folder entitled apache2-default/. Open it and you will see a message saying "It works!" , congrats to you!

Install PHP

In this part we will install PHP 5.

Step 1. Again open up the Terminal (Applications > Accessories > Terminal). Step 2. Copy/Paste the following line into Terminal and press enter:

sudo apt-get install php5 libapache2-mod-php5

Step 3. In order for PHP to work and be compatible with Apache we must restart it. Type the following code in Terminal to do this:

sudo /etc/init.d/apache2 restart

Test PHP -- To ensure there are no issues with PHP let's give it a quick test run.

Step 1. In the terminal copy/paste the following line: updated

sudo gedit /var/www/html/testphp.php

This will open up a file called phptest.php.

Step 2. Copy/Paste this line into the phptest file:

<?php phpinfo(); ?>

Step 3. Save and close the file.

Step 4. Now open you're web browser and type the following into the web address:

http://localhost/testphp.php

The page should look like this:

Good luck!

The path where php file should be stored should be correct. Store your php file of /var/www/html/yourdirectory/filename.php follow above path and then in the browser type:

http://localhost/yourdirectory/filename.php

As long as you have php installed, you run a PHP file using

/usr/bin/php /path/to/php/file.php

Or if your $PATH is set up properly to include /usr/bin, then simply

php /path/to/php/file.php

You can check if PHP is installed, by running

which php