Symfony\Installer\Manager\ComposerManager::getPackageVersion PHP Method

    public function getPackageVersion($packageName)
    {
        $composerLockFileContents = json_decode(file_get_contents($this->projectDir . '/composer.lock'), true);
        foreach ($composerLockFileContents['packages'] as $packageConfig) {
            if ($packageName === $packageConfig['name']) {
                return $packageConfig['version'];
            }
        }
    }

 /**
  * Returns the full Symfony version number of the project by getting
  * it from the composer.lock file.
  *
  * @return string The installed Symfony version
  */
 protected function getInstalledSymfonyVersion()
 {
     $symfonyVersion = $this->composerManager->getPackageVersion('symfony/symfony');
     if (!empty($symfonyVersion) && 'v' === substr($symfonyVersion, 0, 1)) {
         return substr($symfonyVersion, 1);
     }
     return $symfonyVersion;
 }