Show project version in TYPO3 backend

AddProjectVersionToSystemInformationToolbar.php

<?php

declare(strict_types=1);

namespace MyVendor\Sitepackage\EventListener;

use TYPO3\CMS\Backend\Backend\Event\SystemInformationToolbarCollectorEvent;
use TYPO3\CMS\Backend\Backend\ToolbarItems\SystemInformationToolbarItem;
use TYPO3\CMS\Core\Core\Environment;
use TYPO3\CMS\Core\Utility\CommandUtility;

/**
 * Prints the current code version into the System Information Toolbar.
 * The current version is read from
 *  * the PROJECT_VERSION env variable or
 *  * the currently checked out git branch.
 */
class AddProjectVersionToSystemInformationToolbar
{
    public function __invoke(SystemInformationToolbarCollectorEvent $event): SystemInformationToolbarCollectorEvent
    {
        $this->addProjectVersion($event->getToolbarItem());
        return $event;
    }

    protected function addProjectVersion(SystemInformationToolbarItem $systemInformationToolbarItem): void
    {
        $projectVersion = null;
        if (!empty(getenv('PROJECT_VERSION'))) {
            $projectVersion = getenv('PROJECT_VERSION');
        } elseif (is_array($currentMessage = self::runGitcommand('git branch | grep \*'))) {
            $projectVersion = $currentMessage[0];
            if (strpos($projectVersion, '* ') === 0) {
                $projectVersion = substr($projectVersion, 2);
            }
        }

        if (empty($projectVersion)) {
            return;
        }

        $systemInformationToolbarItem->addSystemInformation(
            'Project Version',
            $projectVersion,
            'mimetypes-x-sys_category'
        );
    }

    protected function runGitcommand(string $command): array
    {
        $path = Environment::getPublicPath() . '/';
        CommandUtility::exec('cd ' . $path . ' &&' . $command, $output);
        return $output;
    }
}

Services.yaml

services:
  MyVendor\Sitepackage\EventListener\AddProjectVersionToSystemInformationToolbar:
    tags:
      - name: event.listener
        identifier: 'sitepackage/addProjectVersionToSystemInformationToolbar'
        event: TYPO3\CMS\Backend\Backend\Event\SystemInformationToolbarCollectorEvent