In command prompt type below

set PATH=%PATH%;C:\path\to\php

Where C:\path\to\php is the folder where your php.exe file is located. After this run

C:\>php -v

than you will see something like

PHP 7.3.6 (cli) (built: May 29 2019 12:11:00) 

UPDATE:

If you find that when you restart your computer, this solution will not work anymore:

Set the Path like as following:

Step 1 - Click on the Windows icon

Step 2 - Click on the Settings icon

Step 3 - Click on System

Step 4 - Click on About

Step 5 - Click on System info

Step 6 - Click on Advanced system settings

Step 7 - Click on Environment variables...

Step 8 - Select Path row and then click Edit

Step 9 - Click New and then click Browse, then in the next panel which will open you need to select the folder you want in the Path. For the initial premise of this guide i will add the folder C:\Users\NewFolderInPath

Note: Replace your PHP installed path(e.g:C:\Program Files\php) with the above path .

Step 10 - Click OK and click every OK button you will encounter to close every previous windows.

PHP is a scripting language that commonly has been used to implement a content management systems. It is my recommendation that you move anything that is dependent on PHP to a Linux machine. Microsoft ended their support and involvement of PHP about 5 years ago and at php 8.0. If you want to do like I do, utilize the tools on the system to manage the PHP installations (phpmanager and Windows Platform Installer) you can no longer do that. The infrastructure for both of those are gone (iis.net). Since PHP is an open source project, you can go directly there and get what you want, but you have also now acquired the resposibility for doing it yourself.
On top of that with the age of these servers, you have to also assess the applications that are using PHP. The upgrade from 5.6 to 8.2 isn’t likely to be smooth. Something built for 5.6 is far from being compatible with 8.x You have at least the step from version 5 to 7 and 7 to 8 to consider.

Hi @XR220 ,

I suggest you install php manager in IIS. It can help you manage different versions of php and it is simpler to add new php than configure fastcgi manually. Download it from here.

Please download php from this link and choose the zip:

Please put all php folders in C:\Program Files (x86)\PHP for ease of management. (Web PI also install php in this folder)

1. Click php manager to register new php version.
   
2. Choose the php-cgi.exe of php 7.3.31 and OK.
   
3. Click Change php version to check which version of php is using now.
   
4. Then click Check php info and OK, it will output the version of php.
   

If it doesn't output php version correctly and show error that fastcgi exited unexpectedly, you can use command line to run php-cgi.exe. It will tell you why php run failed. When I tested php 7.3.31, it ran failed because VCRUNTIME140.dll is missing. If you have same issue, please download it from here. Choose the x64 or x86 according to your machine.

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Best regards,
Bruce Zhang

If you are using the PHP CLI, then try using theese shell commands (i'm assuming that you are using linux here)

which php - will locate the php executable (this should be the default php used by you)
whereis php - The first path displayed will be the location of the php executable
echo $PATH - will print a list of paths separated by ":" where the system looks for commands

If you are using PHP as an Apache module then phpinfo() will tell you the php version used, and the php config files, NOT the php path. If you have 2 versions of the php executable then this will help you. If they are the same version then it wont really matter which one is who:)

If you want to find out the php version, then php -v will print the php version in the CLI and any Zend modules installed.

If you want to find out the ini files included then php --ini will display th list of ini files loaded by the php module (this applies for the CLI version).