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Twig tutorial

Twig tutorial shows how to use Twig template engine in PHP applications to generate documents.

Twig

Twig is a PHP template engine. It was created by Symfony developers. Twig files have the extension of .html.twig; they are a mix of static data such as HTML and Twig constructs.

Twig uses the double curly brace delimiters {{ }} for output and the curly brace percentage delimiters {% %} for logic. The {# #} are used for comments.

<ul>
    {% for word in words %}
        <li>{{ word }}</li>
    {% endfor %}
</ul>

This code is a sample Twig syntax. In this code, we use for tag to crate a loop.

Twig syntax consists of tags, filters, functions, operators, and tests.

Setting up Twig

First, we set up Twig.

$ composer require twig/twig

We install Twig with composer.

$ mkdir templates

We will place our template files into the template directory.

require __DIR__ . '/vendor/autoload.php';

We need to add the autoload.php file to our scripts.

Template engine

A template engine or template processor is a library designed to combine templates with a data model to produce documents. Template engines are often used to generate large amounts of emails, in source code preprocessing or producing dynamic HTML pages.

We create a template engine, where we define static parts and dynamic parts. The dynamic parts are later replaced with data. The rendering function later combines the templates with data.

Twig first example

The following is a simple demonstration of the Twig template system.

first.php
<?php

require __DIR__ . '/vendor/autoload.php';

use Twig\Environment;
use Twig\Loader\FilesystemLoader;

$loader = new FilesystemLoader(__DIR__ . '/templates');
$twig = new Environment($loader);

echo $twig->render('first.html.twig', ['name' => 'John Doe', 
    'occupation' => 'gardener']);

We used FilesystemLoader to load templates from the specified directory.

echo $twig->render('first.html.twig', ['name' => 'John Doe', 
    'occupation' => 'gardener']);

The output is generated with render(). It takes two parameters: the template file and the data.

templates/first.html.twig
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <p>
        {{ name }} is a {{ occupation }}
    </p>

</body>

</html>

This is the template file. The variables are output with {{}} syntax.

$ php first.php
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <p>
        John Doe is a gardener
    </p>

</body>

</html>

This is the output.

Twig filters

Filters allow us to modify data in various ways.

filters.php
<?php

require __DIR__ . '/vendor/autoload.php';

use Twig\Environment;
use Twig\Loader\FilesystemLoader;

$loader = new FilesystemLoader(__DIR__ . '/templates');
$twig = new Environment($loader);

$words = ['sky', 'mountain', 'falcon', 'forest', 'rock', 'blue'];
$sentence = 'today is a windy day';

echo $twig->render('filters.html.twig', 
    ['words' => $words, 'sentence' => $sentence]);

In the example, we have an array and a string as template data.

templates/filters.html.twig
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Filters</title>
</head>

<body>

    <p>
     The array has {{ words | length }} elements
    </p>

    <p>
     Joined array elements: {{ words | join(',') }} 
    </p>    

    <p>
     {{ sentence | title }} 
    </p>        

</body>

</html>

Filters are applied with the | character. The example counts words with length, joins array elements with join and modifies characters with title.

Twig custom filters

We can create custom filters with Twig_Filter.

customfilter.php
<?php

require __DIR__ . '/vendor/autoload.php';

use Twig\Environment;
use Twig\Loader\FilesystemLoader;

$loader = new FilesystemLoader(__DIR__ . '/templates');
$twig = new Environment($loader);
$twig->addFilter(new Twig_Filter('accFirst', 'accFirst'));

$sentence = 'šumivé víno';

echo $twig->render('customfilter.html.twig',
    ['sentence' => $sentence]);

function accFirst($value, $encoding = 'UTF8')
{
    $strlen = mb_strlen($value, $encoding);
    $firstChar = mb_substr($value, 0, 1, $encoding);
    $rest = mb_substr($value, 1, $strlen - 1, $encoding);

    return mb_strtoupper($firstChar, $encoding) . $rest;
}

We add a new filter called accFirst. It modifies only the first letter and also handles accents.

templates/customfilter.html.twig
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Custom filter</title>
</head>

<body>  

    <p>
     {{ sentence | accFirst }} 
    </p>      

</body>

</html>

This is the template file, which uses the custom accFirst filter.

Twig loops

To create loops, we use the for tag.

looping.php
<?php

require __DIR__ . '/vendor/autoload.php';

use Twig\Environment;
use Twig\Loader\FilesystemLoader;

$loader = new FilesystemLoader(__DIR__ . '/templates');
$twig = new Environment($loader);

$words = ['sky', 'mountain', 'falcon', 'forest', 
    'rock', 'blue', 'solid', 'book', 'tree'];

echo $twig->render('words.html.twig', ['words' => $words]);

We will loop an array of words.

templates/words.html.twig
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Words</title>
</head>

<body>

    <ul>
    {% for word in words %}
        <li>{{ word }}</li>
    {% endfor %}
    </ul>

    <ul>
    {% for word in words|slice(2, 4) %}
        <li>{{ word }}</li>
    {% endfor %}    
    </ul>

</body>

</html>

In the template file, we loop over the words array and generate an HTML list. With slice() filter, we can loop over a part of the array.

Twig looping with if & else

We can combine the for tag with the if tag and else tags.

looping2.php
<?php

require __DIR__ . '/vendor/autoload.php';

use Twig\Environment;
use Twig\Loader\FilesystemLoader;

$loader = new FilesystemLoader(__DIR__ . '/templates');
$twig = new Environment($loader);

$users = [ 
    ['name' => 'John Doe', 'active' => false],
    ['name' => 'Lucy Smith', 'active' => false],
    ['name' => 'Peter Holcombe', 'active' => false],
    ['name' => 'Barry Collins', 'active' => false]
];

echo $twig->render('activeusers.html.twig', ['users' => $users]);

We send an array of users to the template file.

templates/activeusers.html.twig
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

<p>Active users</p>

<ul>
    {% for user in users if user.active %}
        <li>{{ user.name }}</li>
    {% else %}
        <li>No users found</li>
    {% endfor %}
</ul>

</body>

</html>

We output the user's name of the user.active property is true. When there are no active users, the output from the else tag is shown.

Twig set tag

The set tag allows to set a value to a variable inside a template.

$words = ['sky', 'mountain', 'falcon', 'forest',
    'rock', 'blue', 'solid', 'book', 'tree'];
    
echo $twig->render('test.html.twig', ['words' => $words]);

We have a list of words.

{% set sorted = words | sort %}

<ul>
{% for word in sorted %}
    <li>{{ word }}</li>
{% endfor %}
</ul>

We sort the array with sort filter and assign the sorted array to the sorted variable with set.

Twig verbatim tag

The verbatim marks sections as being raw text that should not be parsed.

{% verbatim %}
    <ul>
    {% for word in words %}
        <li>{{ word }}</li>
    {% endfor %}
    </ul>
{% endverbatim %}

For instance, if we had a tutorial explaing some Twig tag, we would need not to parse a piece of the demonstration.

Twig format filter

The format filter formats a given string by replacing the placeholders. It works like the sprintf() function.

$name = "John Doe";
$age = 34;
        
echo $twig->render('formatfil.html.twig', ['name' => $name, 'age' => $age]);

We send two variables to the template.

{{ "%s is %d years old" | format(name, age) }}

We build the string with format.

Twig date function

The date() function converts an argument to a date to allow date comparison.

$user = ['name' => 'John Doe', 'created_at' => '2011/11/10'];

echo $twig->render('datefun.html.twig', ['user' => $user]);

The user array has a created_at key.

{% if date(user.created_at) < date('-5years') %}
    <p>{{ user.name }} is a senior user</p>
{% endif %} 

In the template, we compare two dates.

Twig automatic escaping

Twig automatically escapes certain characters such as < or >.

$twig = new Environment($loader, [
    'autoescape' => false
]);

Autoescaping can be turned off with the autoescape option.

$data = "<script src='http::/example.com/nastyscript.js'></script>";

echo $twig->render('autoescape.html.twig', ['data' => $data]);

Users could potentionally add dangerous input to the application. The inclusion of unknown JS file can be prevented with autoescaping.

<p>
The data is {{ data }}
</p>

<p>
The data is {{ data | raw }}
</p>

If autoescaping is enabled, we can show the raw input with the raw filter.

<p>
The data is &lt;script src=&#039;http::/example.com/nastyscript.js&#039;&gt;&lt;/script&gt;
</p>

<p>
The data is <script src='http::/example.com/nastyscript.js'></script>
</p>

This partial output shows how the characters are escaped.

Twig tests

Twig tests allow to test data. The tests are applied with the is operator.

$words = ['', null, 'rock', '   ', 'forest'];
echo $twig->render('tests.html.twig', ['words' => $words]);

We have an array of words that contains empty, null, and blank elements.

<ul>
{% for word in words %}

    {% if word is null %}
    <p>null element</p>
    {% elseif word | trim is empty %}
    <p>Empty element</p>
    {% else %}
    <li>{{ word }}</li>
    {% endif %}

{% endfor %}
</ul>

To deal with empty, blank, and null elements, Twig has empty and null tests.

Twig inheritance

Twig's template inheritance is a powerful feature which removes duplication and promotes maintenance.

inheritance.php
<?php

require __DIR__ . '/vendor/autoload.php';

use Twig\Environment;
use Twig\Loader\FilesystemLoader;

$loader = new FilesystemLoader(__DIR__ . '/templates');
$twig = new Environment($loader);

echo $twig->render('derived.html.twig');

This is the inheritance.php file. It renders the derived.html.twig, which extends from base.html.twig.

templates/base.html.twig
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>{% block title %}{% endblock %}</title>
</head>

<body>

{% block body %}{% endblock %}

</body>

</html>

The base layout defines two blocks which are replaced by children: title and body.

templates/derived.html.twig
{% extends 'base.html.twig' %}

{% block title %}Some title{% endblock %}

{% block body %}

The body contents

{% endblock %}

The derived child template inherits from the base template with the extends keyword. The two block define custom text.

$ php inheritance.php
<!DOCTYPE html><html lang="en">
<head>
    <meta charset="UTF-8">    
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Some title</title>
</head>

<body>


The body contents


</body>

</html>

This is the output.

Symfony example

Twig is an integral part of Symfony framework. The next example shows steps to use Twig in a Symfony skeleton application.

$ composer create-project symfony/skeleton simple
$ cd simple

We create a new Symfony skeleton application and move to the project directory.

$ composer require server --dev

We include the development server.

$ composer require maker annotations twig

We include some basic Symfony components including Twig.

$ php bin/console make:controller HomeController

We create a home controller.

src/Controller/HomeController.php
<?php

namespace App\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\Routing\Annotation\Route;

class HomeController extends AbstractController
{
    /**
     * @Route("/home", name="home")
     */
    public function index()
    {
        $words = ['sky', 'blue', 'cloud', 'symfony', 'forest'];

        return $this->render('home/index.html.twig', [
            'words' => $words
        ]);
    }
}

In the home controller, we render the index.html.twig template and pass it the $words array to process.

templates/base.html.twig
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>{% block title %}Welcome!{% endblock %}</title>
        {% block stylesheets %}{% endblock %}
    </head>
    <body>
        {% block body %}{% endblock %}
        {% block javascripts %}{% endblock %}
    </body>
</html>

This is the base layout page.

templates/home/index.html.twig
{% extends 'base.html.twig' %}

{% block title %}Home page{% endblock %}

{% block body %}

<h2>List of words</h2>

<ul>
{% for word in words  %}
    <li>{{ word }}</li>
{% endfor %}
</ul>

{% endblock %}

This is the home page template. It uses the for tag to iterate over the words and output them in an unordered list.

$ php bin/console server:run

We start the server.

We navigate to http://localhost:8000/home to see the result.

In this tutorial, we have used Twig to generate documents from templates and data. We covered Twig tags, filters, tests, and inheritance. We showed Twing in a Symfony application.

You might also be interested in the following related tutorials: PHP Faker tutorial, Respect validation tutorial, Introduction to Symfony, Rakit validation tutorial, PHP PDO tutorial, and PHP tutorial.