How to change PHP version used by composer

I want to use another php version on my machine than the one already installed using WAMP (2 PHP version installed).

• The composer installed uses PHP 5.6
• A new project requires PHP7.0.

Whenever I choose PHP 7 from the control panel of WAMP and then run php -v it still printing PHP5.6 (CLI)... instead of PHP7.

How can I use PHP7 without reinstalling the composer again?

You can change php version of composer without uninstalling it, follow these steps :

1. Search for system environment variables in cortana.
2. Click on the button "Environment variables".
3. Under "System variables" select path and click on edit, you will see one entry like this "C:\wamp\bin\php\php5.6.13".
4. Just change this to the folder name of the php located at your wamp/bin/php7.1.9, here php7.1.9 is folder name.
5. Replace php5.6.13 with bin7.1.9, it will look like these "C:\wamp\bin\php\php7.1.9", just click ok on all the boxes.
6. You are done.
7. To verify, first close all the cmd windows, than open cmd and type php -v, press enter and you should see php7.1.9.
8. If you don't see change in php version than just restart your pc and run php -v again in cmd , it will work.

I'm assuming Windows if you're using WAMP. Composer likely is just using the PHP set in your path: How to access PHP with the Command Line on Windows?

You should be able to change the path to PHP using the same instructions.

Otherwise, composer is just a PHAR file, you can download the PHAR and execute it using any PHP:

C:\full\path\to\php.exe C:\full\path\to\composer.phar install

If anyone is still having trouble, remember you can run composer with any php version that you have installed e.g. $ php7.3 -f /usr/local/bin/composer update

Use which composer command to help locate the composer executable.

Another possibility to make composer think you're using the correct version of PHP is to add to the config section of a composer.json file a platform option, like this:

"config": {
    "platform": {
        "php": "<ver>"
    }
},

Where <ver> is the PHP version of your choice.

Snippet from the docs:

Lets you fake platform packages (PHP and extensions) so that you can emulate a production env or define your target platform in the config. Example: {"php": "7.0.3", "ext-something": "4.0.3"}.