Provided by: libyaml-perl_1.30-1_all bug


       YAML - YAML Ain't Markup Language™


       This document describes YAML version 1.30.


       This module has been released to CPAN as YAML::Old, and soon will be changed to
       just be a frontend interface module for all the various Perl YAML implementation modules,
       including YAML::Old.

       If you want robust and fast YAML processing using the normal Dump/Load API, please
       consider switching to YAML::XS. It is by far the best Perl module for YAML at this time.
       It requires that you have a C compiler, since it is written in C.

       If you really need to use this version of it will always be available as

       The rest of this documentation is left unchanged, until is switched over to the
       new UI-only version.


           use YAML;

           # Load a YAML stream of 3 YAML documents into Perl data structures.
           my ($hashref, $arrayref, $string) = Load(<<'...');
           name: ingy       # A Mapping
           age: old
           weight: heavy
           # I should comment that I also like pink, but don't tell anybody.
           favorite colors:
             - red
             - green
             - blue
           - Clark Evans    # A Sequence
           - Oren Ben-Kiki
           - Ingy döt Net
           --- >            # A Block Scalar
           You probably think YAML stands for "Yet Another Markup Language". It
           ain't! YAML is really a data serialization language. But if you want
           to think of it as a markup, that's OK with me. A lot of people try
           to use XML as a serialization format.

           "YAML" is catchy and fun to say. Try it. "YAML, YAML, YAML!!!"

           # Dump the Perl data structures back into YAML.
           print Dump($string, $arrayref, $hashref);

           # YAML::Dump is used the same way you'd use Data::Dumper::Dumper
           use Data::Dumper;
           print Dumper($string, $arrayref, $hashref);

           Since version 1.25 supports trailing comments.


       The module implements a YAML Loader and Dumper based on the YAML 1.0
       specification. <>

       YAML is a generic data serialization language that is optimized for human readability. It
       can be used to express the data structures of most modern programming languages.
       (Including Perl!!!)

       For information on the YAML syntax, please refer to the YAML specification.


       YAML is readable for people.
           It makes clear sense out of complex data structures. You should find that YAML is an
           exceptional data dumping tool. Structure is shown through indentation, YAML supports
           recursive data, and hash keys are sorted by default. In addition, YAML supports
           several styles of scalar formatting for different types of data.

       YAML is editable.
           YAML was designed from the ground up to be an excellent syntax for configuration
           files. Almost all programs need configuration files, so why invent a new syntax for
           each one? And why subject users to the complexities of XML or native Perl code?

       YAML is multilingual.
           Yes, YAML supports Unicode. But I'm actually referring to programming languages. YAML
           was designed to meet the serialization needs of Perl, Python, Ruby, Tcl, PHP,
           Javascript and Java. It was also designed to be interoperable between those languages.
           That means YAML serializations produced by Perl can be processed by Python.

       YAML is taint safe.
           Using modules like Data::Dumper for serialization is fine as long as you can be sure
           that nobody can tamper with your data files or transmissions. That's because you need
           to use Perl's "eval()" built-in to deserialize the data.  Somebody could add a snippet
           of Perl to erase your files.

           YAML's parser does not need to eval anything.

       YAML is full featured.
           YAML can accurately serialize all of the common Perl data structures and deserialize
           them again without losing data relationships. Although it is not 100% perfect (no
           serializer is or can be perfect), it fares as well as the popular current modules:
           Data::Dumper, Storable, XML::Dumper and Data::Denter.

  also has the ability to handle code (subroutine) references and typeglobs.
           (Still experimental) These features are not found in Perl's other serialization

       YAML is extensible.
           The YAML language has been designed to be flexible enough to solve it's own problems.
           The markup itself has 3 basic construct which resemble Perl's hash, array and scalar.
           By default, these map to their Perl equivalents. But each YAML node also supports a
           tagging mechanism (type system) which can cause that node to be interpreted in a
           completely different manner. That's how YAML can support object serialization and
           oddball structures like Perl's typeglob.


       This module,, is really just the interface module for YAML modules written in
       Perl. The basic interface for YAML consists of two functions: "Dump" and "Load". The real
       work is done by the modules YAML::Dumper and YAML::Loader.

       Different YAML module distributions can be created by subclassing and YAML::Loader
       and YAML::Dumper. For example, YAML-Simple consists of YAML::Simple YAML::Dumper::Simple
       and YAML::Loader::Simple.

       Why would there be more than one implementation of YAML? Well, despite YAML's offering of
       being a simple data format, YAML is actually very deep and complex. Implementing the
       entirety of the YAML specification is a daunting task.

       For this reason I am currently working on 3 different YAML implementations.

           The main YAML distribution will keeping evolving to support the entire YAML
           specification in pure Perl. This may not be the fastest or most stable module though.
           Currently, has lots of known bugs. It is mostly a great tool for dumping Perl
           data structures to a readable form.

           The point of YAML::Tiny is to strip YAML down to the 90% that people use most and
           offer that in a small, fast, stable, pure Perl form. YAML::Tiny will simply die when
           it is asked to do something it can't.

           "libsyck" is the C based YAML processing library used by the Ruby programming language
           (and also Python, PHP and Pugs). YAML::Syck is the Perl binding to "libsyck". It
           should be very fast, but may have problems of its own. It will also require C

           NOTE: Audrey Tang has actually completed this module and it works great and is
                 10 times faster than

       In the future, there will likely be even more YAML modules. Remember, people other than
       Ingy are allowed to write YAML modules!


       YAML is completely OO under the hood. Still it exports a few useful top level functions so
       that it is dead simple to use. These functions just do the OO stuff for you. If you want
       direct access to the OO API see the documentation for YAML::Dumper and YAML::Loader.

   Exported Functions
       The following functions are exported by by default. The reason they are exported
       is so that YAML works much like Data::Dumper. If you don't want functions to be imported,
       just use YAML with an empty import list:

           use YAML ();

           Turn Perl data into YAML. This function works very much like Data::Dumper::Dumper().
           It takes a list of Perl data structures and dumps them into a serialized form. It
           returns a string containing the YAML stream. The structures can be references or plain

           Turn YAML into Perl data. This is the opposite of Dump. Just like Storable's thaw()
           function or the eval() function in relation to Data::Dumper. It parses a string
           containing a valid YAML stream into a list of Perl data structures.

   Exportable Functions
       These functions are not exported by default but you can request them in an import list
       like this:

           use YAML qw'freeze thaw Bless';

       freeze() and thaw()
           Aliases to Dump() and Load() for Storable fans. This will also allow to be
           plugged directly into modules like, that use the freeze/thaw API for internal

       DumpFile(filepath, list)
           Writes the YAML stream to a file instead of just returning a string.

           Reads the YAML stream from a file instead of a string.

       Bless(perl-node, [yaml-node | class-name])
           Associate a normal Perl node, with a yaml node. A yaml node is an object tied to the
           YAML::Node class. The second argument is either a yaml node that you've already
           created or a class (package) name that supports a "yaml_dump()" function. A
           "yaml_dump()" function should take a perl node and return a yaml node. If no second
           argument is provided, Bless will create a yaml node. This node is not returned, but
           can be retrieved with the Blessed() function.

           Here's an example of how to use Bless. Say you have a hash containing three keys, but
           you only want to dump two of them. Furthermore the keys must be dumped in a certain
           order. Here's how you do that:

               use YAML qw(Dump Bless);
               $hash = {apple => 'good', banana => 'bad', cauliflower => 'ugly'};
               print Dump $hash;
               Bless($hash)->keys(['banana', 'apple']);
               print Dump $hash;


               apple: good
               banana: bad
               cauliflower: ugly
               banana: bad
               apple: good

           Bless returns the tied part of a yaml-node, so that you can call the YAML::Node
           methods. This is the same thing that YAML::Node::ynode() returns.  So another way to
           do the above example is:

               use YAML qw(Dump Bless);
               use YAML::Node;
               $hash = {apple => 'good', banana => 'bad', cauliflower => 'ugly'};
               print Dump $hash;
               $ynode = ynode(Blessed($hash));
               $ynode->keys(['banana', 'apple']);
               print Dump $hash;

           Note that Blessing a Perl data structure does not change it anyway. The extra
           information is stored separately and looked up by the Blessed node's memory address.

           Returns the yaml node that a particular perl node is associated with (see above).
           Returns undef if the node is not (YAML) Blessed.


       YAML options are set using a group of global variables in the YAML namespace.  This is
       similar to how Data::Dumper works.

       For example, to change the indentation width, do something like:

           local $YAML::Indent = 3;

       The current options are:

           You can override which module/class YAML uses for Dumping data.

       LoadBlessed (since 1.25)
           Default is undef (false)

           The default was changed in version 1.30.

           When set to true, YAML nodes with special tags will be automatocally blessed into

               - !perl/hash:Foo::Bar
                   foo: 42

           When loading untrusted YAML, you should disable this option by setting it to 0. This
           will also disable setting typeglobs when loading them.

           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

           You can override which module/class YAML uses for Loading data.

           This is the number of space characters to use for each indentation level when doing a
           Dump(). The default is 2.

           By the way, YAML can use any number of characters for indentation at any level. So if
           you are editing YAML by hand feel free to do it anyway that looks pleasing to you;
           just be consistent for a given level.

           Default is 1. (true)

           Tells whether or not to sort hash keys when storing a document.

           YAML::Node objects can have their own sort order, which is usually what you want. To
           override the YAML::Node order and sort the keys anyway, set SortKeys to 2.

           Default is 0. (false)

           Objects with string overloading should honor the overloading and dump the
           stringification of themselves, rather than the actual object's guts.

           Default is 0. (false)

           Values that look like numbers (integers, floats) will be numified when loaded.

           Default is 1. (true)

           This tells whether to use a separator string for a Dump operation.  This only
           applies to the first document in a stream. Subsequent documents must have a YAML
           header by definition.

           Default is 0. (false)

           Tells whether to include the YAML version on the separator/header.

               --- %YAML:1.0

           Default is ''.

           Anchor names are normally numeric. simply starts with '1' and increases by one
           for each new anchor. This option allows you to specify a string to be prepended to
           each anchor number.

           Setting the UseCode option is a shortcut to set both the DumpCode and LoadCode options
           at once. Setting UseCode to '1' tells to dump Perl code references as Perl
           (using B::Deparse) and to load them back into memory using eval(). The reason this has
           to be an option is that using eval() to parse untrusted code is, well, untrustworthy.

           Determines if and how should serialize Perl code references. By default
  will dump code references as dummy placeholders (much like Data::Dumper). If
           DumpCode is set to '1' or 'deparse', code references will be dumped as actual Perl

           LoadCode is the opposite of DumpCode. It tells YAML if and how to deserialize code
           references. When set to '1' or 'deparse' it will use "eval()". Since this is
           potentially risky, only use this option if you know where your YAML has been.

           LoadCode must be enabled also to use the feature of evaluating typeglobs (because with
           the typeglob feature you would be able to set the variable $YAML::LoadCode from a YAML

           When set to true, this option tells the Loader to load hashes into YAML::Node objects.
           These are tied hashes. This has the effect of remembering the key order, thus it will
           be preserved when the hash is dumped again. See YAML::Node for more information.

  uses heuristics to guess which scalar style is best for a given node.
           Sometimes you'll want all multiline scalars to use the 'block' style. If so, set this
           option to 1.

           NOTE: YAML's block style is akin to Perl's here-document.

       UseFold (Not supported anymore since v0.60)
           If you want to force YAML to use the 'folded' style for all multiline scalars, then
           set $UseFold to 1.

           NOTE: YAML's folded style is akin to the way HTML folds text, except smarter.

           YAML has an alias mechanism such that any given structure in memory gets serialized
           once. Any other references to that structure are serialized only as alias markers.
           This is how YAML can serialize duplicate and recursive structures.

           Sometimes, when you KNOW that your data is nonrecursive in nature, you may want to
           serialize such that every node is expressed in full. (ie as a copy of the original).
           Setting $YAML::UseAliases to 0 will allow you to do this. This also may result in
           faster processing because the lookup overhead is by bypassed.

           THIS OPTION CAN BE DANGEROUS. If your data is recursive, this option will cause Dump()
           to run in an endless loop, chewing up your computers memory. You have been warned.

           Default is 1.

           Compresses the formatting of arrays of hashes:

                 foo: bar
                 bar: foo


               - foo: bar
               - bar: foo

           Since this output is usually more desirable, this option is turned on by default.

           Default is 0. (false)

           Adds detection mechanisms to encode strings that resemble numbers with mandatory

           This ensures leading that things like leading/trailing zeros and other formatting are


       YAML is a full featured data serialization language, and thus has its own terminology.

       It is important to remember that although YAML is heavily influenced by Perl and Python,
       it is a language in its own right, not merely just a representation of Perl structures.

       YAML has three constructs that are conspicuously similar to Perl's hash, array, and
       scalar. They are called mapping, sequence, and string respectively.  By default, they do
       what you would expect. But each instance may have an explicit or implicit tag (type) that
       makes it behave differently. In this manner, YAML can be extended to represent Perl's Glob
       or Python's tuple, or Ruby's Bigint.

               A YAML stream is the full sequence of Unicode characters that a YAML
               parser would read or a YAML emitter would write. A stream may contain
               one or more YAML documents separated by YAML headers.

               a: mapping
               foo: bar
               - a
               - sequence

           A YAML document is an independent data structure representation within a stream. It is
           a top level node. Each document in a YAML stream must begin with a YAML header line.
           Actually the header is optional on the first document.

               This: top level mapping
                   - a
                   - YAML
                   - document

           A YAML header is a line that begins a YAML document. It consists of three dashes,
           possibly followed by more info. Another purpose of the header line is that it serves
           as a place to put top level tag and anchor information.

               --- !recursive-sequence &001
               - * 001
               - * 001

           A YAML node is the representation of a particular data structure. Nodes may contain
           other nodes. (In Perl terms, nodes are like scalars. Strings, arrayrefs and hashrefs.
           But this refers to the serialized format, not the in- memory structure.)

       tag This is similar to a type. It indicates how a particular YAML node serialization
           should be transferred into or out of memory. For instance a Foo::Bar object would use
           the tag 'perl/Foo::Bar':

               - !perl/Foo::Bar
                   foo: 42
                   bar: stool

           A collection is the generic term for a YAML data grouping. YAML has two types of
           collections: mappings and sequences. (Similar to hashes and arrays)

           A mapping is a YAML collection defined by unordered key/value pairs with unique keys.
           By default YAML mappings are loaded into Perl hashes.

               a mapping:
                   foo: bar
                   two: times two is 4

           A sequence is a YAML collection defined by an ordered list of elements. By default
           YAML sequences are loaded into Perl arrays.

               a sequence:
                   - one bourbon
                   - one scotch
                   - one beer

           A scalar is a YAML node that is a single value. By default YAML scalars are loaded
           into Perl scalars.

               a scalar key: a scalar value

           YAML has many styles for representing scalars. This is important because varying data
           will have varying formatting requirements to retain the optimum human readability.

       plain scalar
           A plain scalar is unquoted. All plain scalars are automatic candidates for "implicit
           tagging". This means that their tag may be determined automatically by examination.
           The typical uses for this are plain alpha strings, integers, real numbers, dates,
           times and currency.

               - a plain string
               - -42
               - 3.1415
               - 12:34
               - 123 this is an error

       single quoted scalar
           This is similar to Perl's use of single quotes. It means no escaping except for single
           quotes which are escaped by using two adjacent single quotes.

               - 'When I say ''\n'' I mean "backslash en"'

       double quoted scalar
           This is similar to Perl's use of double quotes. Character escaping can be used.

               - "This scalar\nhas two lines, and a bell -->\a"

       folded scalar
           This is a multiline scalar which begins on the next line. It is indicated by a single
           right angle bracket. It is unescaped like the single quoted scalar.  Line folding is
           also performed.

               - >
                This is a multiline scalar which begins on
                the next line. It is indicated by a single
                carat. It is unescaped like the single
                quoted scalar. Line folding is also

       block scalar
           This final multiline form is akin to Perl's here-document except that (as in all YAML
           data) scope is indicated by indentation. Therefore, no ending marker is required. The
           data is verbatim. No line folding.

               - |
                   QTY  DESC          PRICE  TOTAL
                   ---  ----          -----  -----
                     1  Foo Fighters  $19.95 $19.95
                     2  Bar Belles    $29.95 $59.90

           A YAML processor has four stages: parse, load, dump, emit.

           A parser parses a YAML stream.'s Load() function contains a parser.

           The other half of the Load() function is a loader. This takes the information from the
           parser and loads it into a Perl data structure.

           The Dump() function consists of a dumper and an emitter. The dumper walks through each
           Perl data structure and gives info to the emitter.

           The emitter takes info from the dumper and turns it into a YAML stream.

           NOTE: In the parserloader and the dumperemitter code are currently
                 very closely tied together. In the future they may be broken into
                 separate stages.

       For more information please refer to the immensely helpful YAML specification available at


       libyaml-shell-perl contains a script called 'ysh', the YAML shell.  ysh provides a simple,
       interactive way to play with YAML. If you type in Perl code, it displays the result in
       YAML. If you type in YAML it turns it into Perl code.

       To run ysh, (assuming you installed it along with simply type:

           ysh [options]

       Please read the "ysh" documentation for the full details. There are lots of options.


       If you find a bug in YAML, please try to recreate it in the YAML Shell with logging turned
       on ('ysh -L'). When you have successfully reproduced the bug, please mail the LOG file to
       the author (

       WARNING: This is still ALPHA code. Well, most of this code has been around for years...

       BIGGER WARNING: has been slow in the making, but I am committed to having top
       notch YAML tools in the Perl world. The YAML team is close to finalizing the YAML 1.1
       spec. This version of is based off of a very old pre 1.0 spec. In actuality there
       isn't a ton of difference, and this is still fairly useful. Things will get much
       better in the future.


       <> is the mailing list.  This is
       where the language is discussed and designed.

       <> is the official YAML website.

       <> is the YAML 1.2 specification.

       <> is the official YAML wiki.


       ·   YAML::XS


       Ingy döt Net <>


       Copyright 2001-2020. Ingy döt Net.

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

       See <>