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YAML(3)               User Contributed Perl Documentation              YAML(3)




NAME

       YAML - YAML Ain't Markup Languageac


VERSION

       This document describes YAML version 1.24.


NOTE

       This module has been released to CPAN as YAML::Old, and soon YAML.pm
       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 YAML.pm it will always be
       available as YAML::Old.

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


SYNOPSIS

           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
             - green
             - blue
           ---
           - Clark Evans
           - Oren Ben-Kiki
           - Ingy dA9|t Net
           --- >
           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);


DESCRIPTION

       The YAML.pm module implements a YAML Loader and Dumper based on the
       YAML 1.0 specification. <http://www.yaml.org/spec/>

       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.


WHY YAML IS COOL

       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.

           YAML.pm 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 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.


YAML IMPLEMENTATIONS IN PERL

       This module, YAML.pm, 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
       YAML.pm 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.

       YAML
           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, YAML.pm has lots of known
           bugs. It is mostly a great tool for dumping Perl data structures to
           a readable form.

       YAML::Tiny
           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.

       YAML::Syck
           "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 compilation.

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

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


FUNCTIONAL USAGE

       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 YAML.pm 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 ();

       Dump(list-of-Perl-data-structures)
           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 scalars.

       Load(string-containing-a-YAML-stream)
           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 YAML.pm to be plugged directly into modules like POE.pm, that
           use the freeze/thaw API for internal serialization.

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

       LoadFile(filepath)
           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;

           produces:

               ---
               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 $hash;
               Bless($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.

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


GLOBAL OPTIONS

       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:

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

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

       Indent
           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.

       SortKeys
           Default is 1. (true)

           Tells YAML.pm 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.

       Stringify
           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.

       Numify
           Default is 0. (false)

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

       UseHeader
           Default is 1. (true)

           This tells YAML.pm 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.

       UseVersion
           Default is 0. (false)

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

               --- %YAML:1.0

       AnchorPrefix
           Default is ''.

           Anchor names are normally numeric. YAML.pm 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.

       UseCode
           Setting the UseCode option is a shortcut to set both the DumpCode
           and LoadCode options at once. Setting UseCode to '1' tells YAML.pm
           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.

       DumpCode
           Determines if and how YAML.pm should serialize Perl code
           references. By default YAML.pm 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.

       LoadCode
           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.

       Preserve
           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.

       UseBlock
           YAML.pm 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
           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.

       UseAliases
           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.

       CompressSeries
           Default is 1.

           Compresses the formatting of arrays of hashes:

               -
                 foo: bar
               -
                 bar: foo

           becomes:

               - foo: bar
               - bar: foo

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

       QuoteNumericStrings
           Default is 0. (false)

           Adds detection mechanisms to encode strings that resemble numbers
           with mandatory quoting.

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


YAML TERMINOLOGY

       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.

       stream
               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

       document
           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
               is:
                   - a
                   - YAML
                   - document

       header
           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

       node
           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

       collection
           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)

       mapping
           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

       sequence
           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

       scalar
           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
                performed.

       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

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

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

       loader
           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.

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

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

           NOTE: In YAML.pm 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 <http://www.yaml.org/spec/>.


YSH - THE YAML SHELL

       The YAML::Shell distribution provides 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 YAML.pm) simply type:

           ysh [options]

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


BUGS & DEFICIENCIES

       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
       (ingy@cpan.org).

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

       BIGGER WARNING: YAML.pm 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 YAML.pm is based
       off of a very old pre 1.0 spec. In actuality there isn't a ton of
       difference, and this YAML.pm is still fairly useful. Things will get
       much better in the future.


RESOURCES

       <http://lists.sourceforge.net/lists/listinfo/yaml-core> is the mailing
       list.  This is where the language is discussed and designed.

       <http://www.yaml.org> is the official YAML website.

       <http://www.yaml.org/spec/> is the YAML 1.2 specification.

       <http://yaml.kwiki.org> is the official YAML wiki.


SEE ALSO

       o   YAML::XS(3)


AUTHOR

       Ingy dA9|t Net <ingy@cpan.org>


COPYRIGHT AND LICENSE

       Copyright 2001-2017. Ingy dA9|t 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 v5.24.2                      2017-10-30                           YAML(3)

yaml 1.240.0 - Generated Wed Nov 1 16:00:42 CDT 2017
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