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CONTENTS

NAME

YAML::XS - Perl YAML Serialization using XS and libyaml

linux

SYNOPSIS

use YAML::XS;

# Classic functional interface
my $yaml = Dump [ 1..4 ];
my $array = Load $yaml;

# EXPERIMENTAL: Object Oriented interface for YAML 1.2
# Incompatible to functional interface!
my $xs = YAML::XS->new;
my $yaml = $xs->dump([ 1..4 ]);
my $array = $xs->load($yaml);

DESCRIPTION

Kirill Simonov's libyaml is arguably the best YAML implementation. The C library is written precisely to the YAML 1.1 specification. It was originally bound to Python and was later bound to Ruby.

This module is a Perl XS binding to libyaml which offers Perl the best YAML support to date.

This module exports the functions Dump, Load, DumpFile and LoadFile. These functions are intended to work exactly like YAML.pm's corresponding functions. Only Load and Dump are exported by default.

CONFIGURATION

The object oriented interface is described below: "OBJECT ORIENTED INTERFACE"

USING YAML::XS WITH UNICODE

Handling unicode properly in Perl can be a pain. YAML::XS only deals with streams of utf8 octets. Just remember this:

$perl = Load($utf8_octets);
$utf8_octets = Dump($perl);

There are many, many places where things can go wrong with unicode. If you are having problems, use Devel::Peek on all the possible data points.

OBJECT ORIENTED INTERFACE

Since version v0.904.0, EXPERIMENTAL

+++NOTE: This is incompatible with the functional interface and will treat YAML values in a different way.+++

This has two MAJOR differences to the old functional interface:

Object with options

This provides an interface where you create a YAML::XS object with options (instead of the old interface with global variables).

YAML 1.2 Core Schema

It implements the YAML 1.2 Core Schema.

(Note that the functional interface does not implement YAML 1.1, when it comes to loading numbers, booleans, null etc. It implements its own set of rules.)

Here is an (incomplete!) example of values that are treated differently than with the functional interface. YAML values that match a certain pattern, are not loaded as strings, but as other types:

# Functional interface: special values (not compatible to other YAML modules)
- [true, false]                             # booleans
- [null, ~]                                 # undef
- [inf, INF, iNf, iNF, InF, INf, -inf, ...] # Inf
- [100_000]                                 # 100000
- # anything that looks_like_number()       # number

# OOP YAML 1.2 special values
- [true, True, TRUE, false, False, FALSE]   # booleans
- [null, Null, NULL, ~]                     # undef
- [.inf, .Inf, .INF, -.inf, -.Inf, -.INF]   # Inf
- [.nan, .NAN, .NaN]                        # nan
- [42, 0x10, 0o10]                          # dec 42, hex 16, oct 8

For more subtle differences regarding numbers checkout the comprehensive data here:

YAML 1.1 / 1.2 definitions: https://perlpunk.github.io/yaml-test-schema/schemas.html
Test data: https://perlpunk.github.io/yaml-test-schema/data.html

This way the OOP interface is compatible to YAML::PP and YAML processors in other languages supporting YAML 1.2.

load will return the first document in scalar context

The functional interface returns the last.

Numbers don't have string flags
Booleans currently are only preserved for the new builtin booleans

Adding a JSON::PP boolean option for older perls is planned

References, objects, globs, regexes and coderefs cannot be loaded or dumped

This is planned.

Usage

use YAML::XS ();
my $xs = YAML::XS->new;
my $yaml = "foo: bar";

# Load single (first) document:
my $data = $xs->load($yaml);
$yaml = $xs->dump($data);

# Or to load all documents:
my @data = $xs->load($yaml);
$yaml = $xs->dump(@data);

METHODS

new

use YAML::XS;
my $xs = YAML::XS->new(
    # load options
    # require_footer => 0,

    # dump options
    # indent => 2,
    # header => 1,
    # footer => 0,
    # width => 80,
    # anchor_prefix => '',

    # load and dump options
    # utf8 => 0,
);

Options:

indent

Default: 2

Sets the number of spaces for indentation for dumping.

utf8

Default: false

When false, the loader will accept unencoded character strings, and the dumper returns unencoded character strings.

When true, the loader accepts a UTF-8 encoded string of bytes, and the dumper returns a UTF-8 encoded string of bytes. This typically makes sense when you read from / write to a file directly.

Default: 1

Writes a --- before every document

Default: 0

Writes a ... at the end of every document.

width

Set the maximum number of colums for dumping. If a value has too many characters, it will be split into multiple lines.

Default: 0

Can be useful in a use case where you want to make sure you received the complete document from the sender.

anchor_prefix

Default: ''

If set to a string like ANCHOR, anchors and aliases will be prefixed with this instead of just being numbers:

# my $xs = YAML::XS->new( anchor_prefix => 'ANCHOR' );
# my $hash = { some => "mapping" };
# say $xs->dump([$hash, $hash]);
- &ANCHOR1
  some: mapping
- *ANCHOR1

load

my $yaml = <<'EOM';
---
- 23
---
some: mapping
EOM
my $array = $xs->load($yaml);
# [23]
my @documents = $xs->load($yaml);
# (
#   [23],
#   { some => "mapping" }
# )

In scalar context, if the YAML string contains more than one document, it will return the first document.

dump

$yaml = $xs->dump($data);
$yaml = $xs->dump($data1, $data2, $data3);
$yaml = $xs->dump(@data);

LIBYAML

You can find out (since v.079) which libyaml version this module was built with:

my $libyaml_version = YAML::XS::LibYAML::libyaml_version();

SEE ALSO

AUTHORS

Ingy döt Net ingy@ingy.net
Tina Müller <tinita@cpan.org>

COPYRIGHT AND LICENSE

Copyright 2007-2025 - Ingy döt Net

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html