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

Provided by: libyaml-libyaml-perl_0.903.0+ds-1_amd64

NAME

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

SYNOPSIS

           use YAML::XS;

           my $yaml = Dump [ 1..4 ];
           my $array = 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

• $YAML::XS::LoadBlessed (since v0.69)

Default: false.

The default was changed in version 0.81.

When set to false, it will not bless data into objects, which can be a security problem, when loading
YAML from an untrusted source. It will silently ignore the tag and just load the data unblessed.

In PyYAML, this is called SafeLoad.

If set to true, it will load the following YAML as objects:

---
local: !Foo::Bar [a]
perl: !!perl/hash:Foo::Bar { a: 1 }
regex: !!perl/regexp:Foo::Bar pattern

You can create any kind of object with YAML. The creation itself is not the critical part. If the
class has a "DESTROY" method, it will be called once the object is deleted. An example with
File::Temp removing files can be found at <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=862373>.

• $YAML::XS::ForbidDuplicateKeys (since 0.84)

Default: false

When set to true, "Load" will die when encountering a duplicate key in a hash, e.g.

key: value
key: another value

This can be useful for bigger YAML documents where it is not that obvious, and it is recommended to
set it to true. That's also what a YAML loader should do by default according to the YAML
specification.

• $YAML::XS::UseCode

• $YAML::XS::DumpCode

• $YAML::XS::LoadCode

If enabled supports deparsing and evaling of code blocks.

Note that support for loading code was added in version 0.75, although $LoadCode was documented
already in earlier versions.

• $YAML::XS::QuoteNumericStrings

When true (the default) strings that look like numbers but have not been numified will be quoted when
dumping.

This ensures leading that things like leading zeros and other formatting are preserved.

• $YAML::XS::Boolean (since v0.67)

Default: undef

Since YAML::XS 0.89: When used with perl 5.36 or later, builtin booleans will work out of the box.
They will be created by "Load" and recognized by "Dump" automatically (since YAML::XS 0.89).

say Dump({ truth => builtin::true });
# truth: true

Since YAML::XS v0.902: loaded booleans are not set to readonly anymore.

For older perl versions you can use the following configuration to serialize data as YAML booleans:

When set to "JSON::PP" or "boolean", the plain (unquoted) strings "true" and "false" will be loaded
as "JSON::PP::Boolean" or "boolean.pm" objects. Those objects will be dumped again as plain "true" or
"false".

It will try to load [JSON::PP] or [boolean] and die if it can't be loaded.

With that it's possible to add new "real" booleans to a data structure:

local $YAML::XS::Boolean = "JSON::PP"; # or "boolean"
my $data = Load("booltrue: true");
$data->{boolfalse} = JSON::PP::false;
my $yaml = Dump($data);
# boolfalse: false
# booltrue: true

It also lets booleans survive when loading YAML via YAML::XS and encode it in JSON via one of the
various JSON encoders, which mostly support JSON::PP booleans.

Please note that JSON::PP::Boolean and boolean.pm behave a bit differently. Ideally you should only
use them in boolean context.

If not set, booleans are loaded as special perl variables "PL_sv_yes" and "PL_sv_no", which have the
disadvantage that they are readonly, and you can't add those to an existing data structure with pure
perl.

If you simply need to load "perl booleans" that are true or false in boolean context, you will be
fine with the default setting.

• $YAML::XS::Indent (since v0.76)

Default is 2.

Sets the number of spaces for indentation for "Dump".

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.

LIBYAML

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

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

AUTHOR

       Ingy döt Net ingy@ingy.net <mailto:ingy@ingy.net>

COPYRIGHT AND LICENSE

       Copyright 2007-2024 - 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>

perl v5.40.0                                       2025-02-07                                      YAML::XS(3pm)