Classes/Console/Command/UpgradeCommandController.php
public function subProcessCommand($upgradeCommand, $arguments)
    {
        $arguments = unserialize($arguments, ['allowed_classes' => false]);
        $result = $this->upgradeHandling->$upgradeCommand(...$arguments);
        $this->output(serialize($result));
    }
public function subProcessCommand($upgradeCommand, $arguments)
    {
        $arguments = unserialize($arguments, ['allowed_classes' => false]);
        $result = $this->upgradeHandling->$upgradeCommand(...$arguments);
        $this->output(serialize($result));
    }
This is where the hard work happens in a fully bootstrapped TYPO3
It will be called as sub process

@param string $upgradeCommand
@param string $arguments Serialized arguments
@internal