Skip to content


Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Perl Prolog Perl6

Fetching latest commit…

Cannot retrieve the latest commit at this time

Failed to load latest commit information.


    YAML - YAML Ain't Markup Language (tm)

        use YAML;
        # Load a YAML stream of 3 YAML documents into Perl data structures.
        my ($hashref, $arrayref, $string) = Load(<<'...');
        name: ingy
        age: old
        weight: heavy
        # I should comment that I also like pink, but don't tell anybody.
        favorite colors:
            - red
            - white
            - blue
        - Clark Evans
        - Oren Ben-Kiki
        - Brian Ingerson
        --- >
        You probably think YAML stands for "Yet Another Markup Language". It
        ain't! YAML is really a data serialization language. But if you want
        to think of it as a markup, that's OK with me. A lot of people try
        to use XML as a serialization format.
        "YAML" is catchy and fun to say. Try it. "YAML, YAML, YAML!!!"
        # Dump the Perl data structures back into YAML.
        print Dump($string, $arrayref, $hashref); 
        # YAML::Dump is used the same way you'd use Data::Dumper::Dumper
        use Data::Dumper;
        print Dumper($string, $arrayref, $hashref); 

    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

    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 any YAML serialization produced by Perl can be processed by
        Python, and be guaranteed to return the data structure intact. (Even
        if it contained Perl specific structures like GLOBs)

    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 modules.

    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 type (or
        "transfer method") which can cause that node to be interpreted in a
        completely different manner. That's how YAML can support oddball
        structures like Perl's typeglob.

  Exported Functions
    The following functions are exported by by default when you use like this:

        use YAML;

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

        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
    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;


            --- #YAML:1.0
            apple: good
            banana: bad
            cauliflower: ugly
            --- #YAML:1.0
            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(:all);
            use YAML::Node;
            $hash = {apple => 'good', banana => 'bad', cauliflower => 'ugly'};
            print Dump $hash;
            $ynode = ynode(Blessed($hash));
            $ynode->keys(['banana', 'apple']);
            print Dump $hash;

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

        Alias to Dump(). For Data::Dumper fans.

    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

  Exportable Function Groups
    This is a list of the various groups of exported functions that you can
    import using the following syntax:

        use YAML ':groupname';

    all Imports Dump(), Load(), DumpFile(), LoadFile(), Bless() and

    POE Imports freeze() and thaw().

        Imports freeze() and thaw().

  Class Methods
    YAML can also be used in an object oriented manner. At this point it
    offers no real advantage. This interface will be improved in a later

        New returns a new YAML object. For example:

            my $y = YAML->new;
            $y->dump($foo, $bar);

  Object Methods
        OO version of Dump().

        OO version of Load().

    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:

        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

        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 1. (true)

        Tells whether to include the YAML version on the

        The canonical form is:

            --- YAML:1.0

        Default is 1. (true)

        Tells whether or not to sort hash keys when storing a

        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 ''.

        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. Safe deserialization is one of the core goals of

        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 code.

        DumpCode can also be set to a subroutine reference so that you can
        write your own serializing routine. passes you the code ref.
        You pass back the serialization (as a string) and a format
        indicator. The format indicator is a simple string like: 'deparse'
        or 'bytecode'.

        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 can also be set to a subroutine reference so that you can
        write your own deserializing routine. passes the
        serialization (as a string) and a format indicator. You pass back
        the code reference.

    UseBlock 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.

        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

        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.

    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 it's 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 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 bytes 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.

            --- YAML:1.0
            This: top level mapping
                - a
                - YAML
                - document

        A YAML node is the representation of a particular data stucture.
        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.)

    transfer method
        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 transfer '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 key/value pairs. 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
        This is a single line of unquoted text. All plain scalars are
        automatic candidates for "implicit transferring". This means that
        their type is determined automatically by examination. Unless they
        match a set of predetermined YAML regex patterns, they will raise a
        parser exception. 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
        and no implicit transfer. It must be used on a single line.

            - '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. There is no implicit transfer and it must still be
        single line.

            - "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 closing brace. 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

        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

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

        NOTE: In the parser/loader and the dumper/emitter code are
        currently very closely tied together. When libyaml is written (in C)
        there will be a definite separation. libyaml will contain a parser
        and emitter, and (and etc) will supply the loader
        and dumper.

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

ysh - The YAML Shell
    The YAML distribution ships with 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 ysh 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 *ALPHA* code.

    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 code 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

    Circular Leaves
        YAML is quite capable of serializing circular references. And for
        the most part it can deserialize them correctly too. One notable
        exception is a reference to a leaf node containing itself. This is
        hard to do from pure Perl in any elegant way. The "canonical"
        example is:

            $foo = \$foo;

        This serializes fine, but I can't parse it correctly yet.
        Unfortunately, every wiseguy programmer in the world seems to try
        this first when you ask them to test your serialization module. Even
        though it is of almost no real world value. So please don't report
        this bug unless you have a pure Perl patch to fix it for me.

        By the way, similar non-leaf structures Dump and Load just fine:

            $foo->[0] = $foo;

        You can test these examples using 'ysh -r'. This option makes sure
        that the example can be deserialized after it is serialized. We call
        that "roundtripping", thus the '-r'.

        Unicode is not yet supported. The YAML specification dictates that
        all strings be unicode, but this early implementation just uses

    Structured Keys
        Python, Java and perhaps others support using any data type as the
        key to a hash. YAML also supports this. Perl5 only uses strings as
        hash keys. can currently parse structured keys, but their meaning gets
        lost when they are loaded into a Perl hash. Consider this example
        using the YAML Shell:

            ysh > ---
            yaml> ?
            yaml>  foo: bar
            yaml> : baz
            yaml> ...
            $VAR1 = {
                      'HASH(0x1f1d20)' => 'baz'
            ysh > will need to be fixed to preserve these keys somehow. Why?
        Because if gets a YAML document from it must be able
        to return it with the Python data intact.

    Globs, Subroutines, Regexes and File Handles
        As far as I know, other Perl serialization modules are not capable
        of serializing and deserializing typeglobs, subroutines (code refs),
        regexes and file handles. has dumping capabilities for all
        of these. Loading them may produce wild results. Take care.

        NOTE: For a (huge) dump of Perl's global guts, try:

            perl -MYAML -e '$YAML::UseCode=1; print Dump *::'

        To limit this to a single namespace try:

            perl -MCGI -MYAML -e '$YAML::UseCode=1; print Dump \%CGI::'

        This is a pure Perl implementation that has been optimized for
        programmer readability, not for computational speed.

        Oren Ben-Kiki and Clark Evans are currently developing libyaml, the
        official C implementation of the YAML parser and emitter.
        will be refactoring to use this library once it is stable. Other
        languages like Python, Tcl, PHP, Ruby, JavaScript and Java can make
        use of the same core library.

        Autrijus Tang is also currently developing libyaml-haskell, the
        haskell parser for YAML. Due to the complexity of the YAML grammar
        it is expected it will take him 87 minutes to complete this.

        Please join us on the YAML mailing list if you are interested in
        implementing something. Or try dropping into "#yaml" on "freenode",
        if that's your style.


    Streaming Access
        This module Dumps and Loads in one operation. There is no interface
        for parsing or emitting a YAML stream one node at a time. It's all
        or nothing.

        An upcoming release will have support for incremental parsing and
        dumping. Stay tuned.

    Please read YAML::Node for advanced YAML features.

    <> is the official YAML website.

    <> is the YAML 1.0 specification.

    <> is the official YAML wiki.

    YAML has been registered as a Source Forge project.
    (<>) Currently we are only using the mailing
    list facilities there.

    Brian Ingerson <> is resonsible for

    The YAML language is the result of a ton of collaboration between Oren
    Ben-Kiki, Clark Evans and Brian Ingerson. Several others have added help
    along the way.

    Copyright (c) 2001, 2002, 2005. Brian Ingerson. All rights reserved.

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

    See <>

Something went wrong with that request. Please try again.