YAML::XS(3pm) User Contributed Perl Documentation YAML::XS(3pm)
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();
SEE ALSO
• YAML.pm
• YAML::Syck
• YAML::Tiny
• YAML::PP
• YAML::PP::LibYAML
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)
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