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

NAME
       YAML - YAML Ain't Markup Language (tm)

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 dt 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 specifica-
       tion.

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 program-
	   ming 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 struc-
	   tures and deserialize them again without losing data relationships.
	   Although it is not 100% perfect (no serializer is or can be per-
	   fect), 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 mod-
       ules 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 implementa-
       tions.

       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::Lite
	   The point of YAML::Lite is to strip YAML down to the 90% that peo-
	   ple use most and offer that in a small, fast, stable, pure Perl
	   form.  YAML::Lite 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 strucures 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 contain-
	   ing 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 docu-
	   ment.

	   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.

       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 separa-
	   tor/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 refer-
	   ences. By default YAML.pm will dump code references as dummy place-
	   holders (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. YAML.pm 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
	   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. YAML.pm passes the serializa-
	   tion (as a string) and a format indicator. You pass back the code
	   reference.

       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 multi-
	   line 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 pro-
	   cessing 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.

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 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.)

       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 ele-
	   ments. 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 sclar is unquoted. All plain scalars are automatic candi-
	   dates 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 escap-
	   ing except for single quotes which are escaped by using two adja-
	   cent 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 struc-
	   ture.

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

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

	   NOTE: In YAML.pm the parser/loader and the dumper/emitter 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 speci-
       fication available at <http://www.yaml.org/spec/>.

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 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 repro-
       duced 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 dif-
       ference, 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 1.0 specification.

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

SEE ALSO
       See YAML::Syck. Fast!

AUTHOR
       Ingy dt Net <ingy@cpan.org>

       is resonsible for YAML.pm.

       The YAML serialization language is the result of years of collaboration
       between Oren Ben-Kiki, Clark Evans and Ingy dt Net. Several others have
       added help along the way.

COPYRIGHT
       Copyright (c) 2005, 2006. Ingy dt Net. All rights reserved.

       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 <http://www.perl.com/perl/misc/Artistic.html>

perl v5.8.8			  2007-04-08			       YAML(3)
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