private void printAll(PrintWriter writer, EnvironmentVariableHandler handler) {
    List<Pair<String, String>> shellEnvs = handler.getAllEnvironmentVariables();
    for (Pair<String, String> pair : shellEnvs) {
      printVariable(writer, pair.getL(), pair.getR());
    }
  }
retrieves the list of {@link CommandHandler}s setup in this environment
@return List of {@link CommandHandler}
samza-sql-shell/src/main/java/org/apache/samza/sql/client/cli/CliEnvironment.java