Fast

One of the goals of Symfony Yaml is to find the right balance between speed and features. It supports just the needed features to handle configuration files. Notable lacking features are: document directives, multi-line quoted messages, compact block collections and multi-document files.

Real Parser

It sports a real parser and is able to parse a large subset of the YAML specification, for all your configuration needs. It also means that the parser is pretty robust, easy to understand, and simple enough to extend.

Clear Error Messages

Whenever you have a syntax problem with your YAML files, the library outputs a helpful message with the filename and the line number where the problem occurred. It eases the debugging a lot.

Dump Support

It is also able to dump PHP arrays to YAML with object support, and inline level configuration for pretty outputs.

Types Support

It supports most of the YAML built-in types like dates, integers, octals, booleans, and much more...

Full Merge Key Support

Full support for references, aliases, and full merge key. Don't repeat yourself by referencing common configuration bits.

Reading YAML Files

The parse() method parses a YAML string and converts it to a PHP array:

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use Symfony\Component\Yaml\Yaml;

$value = Yaml::parse(file_get_contents('/path/to/file.yml'));

If an error occurs during parsing, the parser throws a ParseException exception indicating the error type and the line in the original YAML string where the error occurred:

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use Symfony\Component\Yaml\Exception\ParseException;

try {
    $value = Yaml::parse(file_get_contents('/path/to/file.yml'));
} catch (ParseException $e) {
    printf("Unable to parse the YAML string: %s", $e->getMessage());
}

Writing YAML Files

The dump() method dumps any PHP array to its YAML representation:

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use Symfony\Component\Yaml\Yaml;

$array = array(
    'foo' => 'bar',
    'bar' => array('foo' => 'bar', 'bar' => 'baz'),
);

$yaml = Yaml::dump($array);

file_put_contents('/path/to/file.yml', $yaml);

If an error occurs during the dump, the parser throws a DumpException exception.

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foo: bar
bar:
    foo: bar
    bar: baz

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echo Yaml::dump($array, 1);

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foo: bar
bar: { foo: bar, bar: baz }

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echo Yaml::dump($array, 2);

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foo: bar
bar:
    foo: bar
    bar: baz

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// use 8 spaces for indentation
echo Yaml::dump($array, 2, 8);

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foo: bar
bar:
        foo: bar
        bar: baz

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parameters:
    credit_card_number: 1234_5678_9012_3456
    long_number: 10_000_000_000
    pi: 3.14159_26535_89793
    hex_words: 0x_CAFE_F00D

Object Parsing and Dumping

You can dump objects by using the DUMP_OBJECT flag:

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$object = new \stdClass();
$object->foo = 'bar';

$dumped = Yaml::dump($object, 2, 4, Yaml::DUMP_OBJECT);
// !php/object:O:8:"stdClass":1:{s:5:"foo";s:7:"bar";}

And parse them by using the PARSE_OBJECT flag:

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$parsed = Yaml::parse($dumped, Yaml::PARSE_OBJECT);
var_dump(is_object($parsed)); // true
echo $parsed->foo; // bar

The YAML component uses PHP's serialize() method to generate a string representation of the object.

Handling Invalid Types

By default the parser will encode invalid types as null. You can make the parser throw exceptions by using the PARSE_EXCEPTION_ON_INVALID_TYPE flag:

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$yaml = '!php/object:O:8:"stdClass":1:{s:5:"foo";s:7:"bar";}';
Yaml::parse($yaml, Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE); // throws an exception

Similarly you can use DUMP_EXCEPTION_ON_INVALID_TYPE when dumping:

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$data = new \stdClass(); // by default objects are invalid.
Yaml::dump($data, 2, 4, Yaml::DUMP_EXCEPTION_ON_INVALID_TYPE); // throws an exception

echo $yaml; // { foo: bar }

Date Handling

By default the YAML parser will convert unquoted strings which look like a date or a date-time into a Unix timestamp; for example 2016-05-27 or 2016-05-27T02:59:43.1Z (ISO-8601):

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Yaml::parse('2016-05-27'); // 1464307200

You can make it convert to a DateTime instance by using the PARSE_DATETIME flag:

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$date = Yaml::parse('2016-05-27', Yaml::PARSE_DATETIME);
var_dump(get_class($date)); // DateTime

Dumping Multi-line Literal Blocks

In YAML multiple lines can be represented as literal blocks, by default the dumper will encode multiple lines as an inline string:

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$string = array("string" => "Multiple\nLine\nString");
$yaml = Yaml::dump($string);
echo $yaml; // string: "Multiple\nLine\nString"

You can make it use a literal block with the DUMP_MULTI_LINE_LITERAL_BLOCK flag:

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$string = array("string" => "Multiple\nLine\nString");
$yaml = Yaml::dump($string, 2, 4, Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK);
echo $yaml;
//  string: |
//       Multiple
//       Line
//       String

Parsing PHP Constants

By default, the YAML parser treats the PHP constants included in the contents as regular strings. Use the PARSE_CONSTANT flag and the special !php/const: syntax to parse them as proper PHP constants:

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$yaml = '{ foo: PHP_INT_SIZE, bar: !php/const:PHP_INT_SIZE }';
$parameters = Yaml::parse($yaml, Yaml::PARSE_CONSTANT);
// $parameters = array('foo' => 'PHP_INT_SIZE', 'bar' => 8);

Syntax Validation

The syntax of YAML contents can be validated through the CLI using the LintCommand command.

First, install the Console component:

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$ composer require symfony/console

Create a console application with lint:yaml as its only command:

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// lint.php

use Symfony\Component\Console\Application;
use Symfony\Component\Yaml\Command\LintCommand;

(new Application('yaml/lint'))
    ->add(new LintCommand())
    ->getApplication()
    ->setDefaultCommand('lint:yaml', true)
    ->run();

Then, execute the script for validating contents:

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# validates a single file
$ php lint.php path/to/file.yml

# or all the files in a directory
$ php lint.php path/to/directory

# or contents passed to STDIN
$ cat path/to/file.yml | php lint.php

The result is written to STDOUT and uses a plain text format by default. Add the --format option to get the output in JSON format:

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$ php lint.php path/to/file.yml --format json