How to tell and force Composer to use a specific PHP version such as 7.x or 8.x

To tell Composer to use a specific PHP version, you can use the --php option when installing or updating packages.

For example, to install packages using PHP 8.0, you can use the following command:

composer install --php=8.0

To update packages using PHP 7.4, you can use the following command:

composer update --php=7.4

By default, Composer will use the PHP version specified in the composer.json file. If you want to force Composer to use a specific PHP version, you can add the php key to the composer.json file and set it to the desired version.

For example, to force Composer to use PHP 7.4, you can add the following line to the composer.json file:

"php": "7.4"

Then, when you run composer install or composer update, Composer will use PHP 7.4 regardless of the version specified in the composer.json file.