/ 
YAML-0.25
River stage four • 629 direct dependents • 2064 total dependents
/ YAML

NAME

YAML - Yet Another Markup Language

SYNOPSIS

use YAML;

my ($hashref, $arrayref, $string) = Load(<<'--END');
---
name: ingy
age: old
weight: heavy
favorite colors:
 - red
 - white
 - blue
---
- clark
- oren
- ingy
--- \
YAML should really stand for "YAML Ain't a Markup Language". That's
because it's really a data serialization language. But "YAML" is
just so catchy and fun to say. Try it. "YAML, YAML, YAML!!!"
--END

print Store($string, $arrayref, $hashref); 

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/index.html)

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 at http://www.yaml.org/cce-19.html.

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 the ultimate syntax for configuration files. All 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, Tcl, PHP, 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.

YAML is extensible.

YAML 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.

USAGE

Exported Functions

The following functions are exported by YAML.pm by default when you use YAML.pm like this:

use YAML;

To prevent YAML.pm from exporting functions, say:

use YAML ();
Store(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 stuctures can references or plain scalars.

Load(string containing a YAML stream)

Turn YAML into Perl data. This is the opposite of Data::Dumper; kind of like the eval() function. It parse a string containing a valid YAML stream into a list of Perl data structures. In list context YAML will return a stucture for each YAML document in the stream.

Exportable Functions

StoreFile(filepath, list)
LoadFile(filepath, list)
Dumper()

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

Eval()

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

Indent()

Alias to Store(). For Data::Denter fans.

Undent()

Alias to Load(). For Data::Denter fans.

Denter()

Alias to Store(). For Data::Denter fans.

freeze()

Alias to Store(). For Storable fans.

This will also allow YAML.pm to be plugged directly into POE.pm.

thaw()

Alias to Load(). For Storable fans.

This will also allow YAML.pm to be plugged directly into POE.pm.

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 Store(), Load(), StoreFile() and LoadFile().

POE

Imports freeze() and thaw().

Dumper

Imports Dumper() and Eval().

Denter

Imports Denter(), Indent() and Undent().

Storable

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 may change.

new()

New returns a new YAML object. Options may be passed in as key/value pairs. For example:

my $y = YAML->new(Separator => '--foo',
                  SortKeys => 0,
                 );
$y->store($foo, $bar);

Object Methods

store()

OO version of Store().

load()

OO version of Load().

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 separator string, do something like:

$YAML::Separator = '--<$>';

The current options are:

Separator

Default is '---'.

This is the MIME like string that separates YAML documents in a stream. It must start with two dashes, and then be followed by one or more non-whitespace characters.

UseHeader

Default is 1. (true)

This tells YAML.pm whether use a separator string for a Store operation.

NOTE: It is illegal to not begin a YAML stream with a separator if there are more than one documents in the YAML stream.

UseVersion

Default is 1. (true)

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

The canonical form is:

--- YAML:1.0
SortKeys

Default is 1. (true)

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

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 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 map, sequence, and scalar 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.

stream

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 separators.

---
a: map
foo: bar
---
- a
- sequence
document

A YAML document is an independent data structure representation within a stream. It is a top level node.

--- YAML:1.0
This: top level map
is:
 - a
 - YAML
 - document
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.)

collection

A collection is a YAML data grouping. YAML has two types of collections: maps and sequences. (Similar to hashes and arrays)

map

A map is a YAML collection defined by key/value pairs. By default YAML maps are loaded into Perl hashes.

a map:
 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 six styles for representing scalars. This is important because varying data will have varying formatting requirements to retain the optimum human readability.

implicit scalar

This is a single line of unquoted text. All implicit scalars are automatic candidates for "implicit transferring". This means that unless they match a set of predetermined YAML regex patterns, they will raise a parser exception. The typical uses for this are simple alpha strings, integers, real numbers, dates, times and currency.

- a simple string
- -42
- 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"
plain scalar

This is a multiline scalar which begins on the next line. It is indicated by a single backslash. 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 backslash. It is unescaped like
 the single quoted scalar. Line folding is
 also performed.
escaped scalar

This is a multiline scalar which begins on the next line. It is indicated by a double backslash. It is escaped like the double quoted scalar and subject to line folding.

- \\ 
 This is a multiline scalar which
 begins on the next line.\nIt is
 indicated by a double backslash.\nIt
 is escaped like the double quoted
 scalar and subject to line folding.
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 escaping, no line folding.

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

For more information please refer to the immensely helpful YAML specification available at http://www.yaml.org/spec/index.html

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, cd into the distribution directory and type:

perl ysh

If you find a bug in YAML, please try to recreate it in 'ysh'. If you start ysh with -l, logging will be appended to the file ./ysh.log. If you start ysh with the -L flag, the log will be reset before logging begins.

perl ysh -l
perl ysh -L

When you have successfully reproduced the bug, please mail the LOG file to the author (ingy@cpan.org).

NOTE: The ysh script does not get installed into your path by 'make install'. If you want ysh to be in, say, /usr/local/bin, you should move it there yourself. You'll also need to change the '#!' line to point to your perl binary, if you're using Unix.

BUGS & DEFICIENCIES

WARNING: This is *ALPHA* code. It is brand spanking new. It probably has lots of bugs and speling mistakes.

If you find a bug in YAML, please try the reproduce it with the YAML Shell (ysh) with logging turned on. (See the YAML Shell section above)

BIGGER WARNING: This is *TRIAL1* of the YAML 1.0 specification. The YAML syntax may change before it is finalized. Based on past experience, it probably will change. The authors of this spec have worked for the past six months putting together YAML 1.0, and we have flipped it on it's syntactical head almost every week. We're a fickle lot, we are. So use this at your own risk!!!

(OK, don't get too scared. We *are* pretty happy with the state of things right now. And we *have* agreed to freeze this TRIAL1 for the next couple of months to get user feedback. At the end of the trial period, the syntax may end up changing slightly, but the spirit should remain the same.)

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 Store and Load just fine:

$foo->[0] = $foo;
Unicode

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

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. YAML.pm doesn't have any support for these structured keys yet.

Yet? Why would a Perl5 module need to support these? Because if YAML.pm gets a YAML document from YAML.py it must be able to return it with the Python data intact.

Tuples and Others

YAML.pm will also support other non-Perl data structures like Python's tuples. In this case, and many others, Perl will still be able to make partial use of the foreign critters, because YAML.pm will attempt to map them into something close. Since a Python tuple is close to a Perl array, that's what YAML.pm will map it into. It will then either tie or bless the array into the special class 'org.yaml.tuple', so it can keep track of what the structure originally was. In this way, a Perl program can still make intuitive use of the structure.

'org.yaml.tuple' and other special types have not yet been implemented.

Globs, Subroutines, Regexes and Tied Data

As far as I know, other Perl serialization modules are not capable of serializing and deserializing typeglobs, subroutines (code refs), regexes and tied data structures. YAML may be able to do this at least to some degree of success. No attempt has been made for this alpha implementation.

NOTE: I went ahead and added preliminary glob support for Store only. Example? For a dump of Perl's global guts, try:

perl -MYAML -e 'print Store \%main::'
Speed

This is a pure Perl implementation that has been optimized for programmer readability, not for computational speed. The hope is that others will be able to quickly convert this module into other languages like Python, Tcl, PHP, Ruby, JavaScript and Java.

Eventually there will be a core library, libyaml, written in C. Most implementations, including this one, should be migrated to use that core library.

Please join us on the YAML mailing list if you are interested in implementing something.

https://lists.sourceforge.net/lists/listinfo/yaml-core

RESOURCES

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

YAML has been registered as a Source Forge project. (http://www.sourceforge.net) Currently we are only using the mailing list facilities there.

IMPLEMENTATIONS

This is the first implementation of YAML functionality based on the 1.0 specification.

The following people have shown an interest in doing implementations. Please contact them if you are also interested in writing an implementation.

-
 name: ingy
 project: YAML.pm
 email: ingy@ttul.org
-
 name: Clark Evans
 project: libyaml
 email: cce@clarkevans.com
-
 name: Oren Ben-Kiki
 project: Java Loader/Dumper
 email: orenbk@richfx.com
-
 name: Paul Prescod
 project: YAML Antagonist/Anarchist
 email: paul@prescod.net
-
 name: Patrick Leboutillier
 project: Java Loader/Dumper
 email: patrick_leboutillier@hotmail.com
-
 name: Shane Caraveo
 project: PHP Loader/Dumper
 email: shanec@activestate.com
-
 name: Neil Kandalgoankar
 project: Python Loader/Dumper
 email: neil_j_k@yahoo.com
-
 name: Brian Quinlan
 project: Python Loader/Dumper
 email: brian@sweetapp.com
-
 name: Jeff Hobbs
 project: Tcl Loader/Dumper
 email: jeff@hobbs.org
-
 name: Claes Jacobsson
 project: JavaScript Loader/Dumper
 email: claes@contiller.se
-
 name: Neil Watkiss
 project: YAML mode for the vim editor
 email: nwatkiss@ttul.org

AUTHOR

Brian Ingerson <INGY@cpan.org>

COPYRIGHT

Copyright (c) 2001. 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