Load .env file in Jenkins https://sorokin.engineer/posts/en/jenkins_load_env_vars_with_expanding.html

loadVarsFromFile.groovy

private void loadVarsFromFile(String path) {
    def file = readFile(path)
        .replaceAll("(?m)^\\s*\\r?\\n", "")  // skip empty line
        .replaceAll("(?m)^#[^\\n]*\\r?\\n", "")  // skip commented lines
    file.split('\n').each { envLine ->
        def (key, value) = envLine.tokenize('=')
        env."${key}" = "${value.trim().replaceAll('^\"|\"$', '')}"
    }
}