FeatureContext.php

<?php

// ...

class FeatureContext extends MinkContext
{
    protected $guestsName;
    // ...
    
    /**
     * @Given /I am a guest named "([^"]+)"/
     */
    public function nameGuest($name)
    {
        $this->guestsName = $name;
    }
    
    /**
     * @Given /I fill out the guest book form/
     */
    public function fillGuestBookForm()
    {
        $this->fillField('name', $this->guestsName);
        // ...
    }
}

GuestBook.feature

Feature: GuestBook
  In order to track all of my visitors
  As an admin
  I want to give users the ability to sign my guestbook

  Background:
    Given I am a guest named "John Doe"

  Scenario: With Valid Credentials
    Given there are no guests
    And I am on "guests/create"
    And I fill out the guest book form
    Then I should see "Guest Book"
    And I should see "John Doe"