NAME
YAML::Tiny - Read/Write YAML files with as little code as possible
PREAMBLE
The YAML specification is huge. Really, really huge. It contains all the
functionality of XML, except with flexibility and choice, which makes it
easier to read, but with a formal specification that is more complex
than XML.
The original pure-Perl implementation YAML costs just over 4 megabytes
of memory to load. Just like with Windows .ini files (3 meg to load) and
CSS (3.5 meg to load) the situation is just asking for a YAML::Tiny
module, an incomplete but correct and usable subset of the
functionality, in as little code as possible.
Like the other "::Tiny" modules, YAML::Tiny has no non-core
dependencies, does not require a compiler to install, is back-compatible
to Perl 5.004, and can be inlined into other modules if needed.
In exchange for this adding this extreme flexibility, it provides
support for only a limited subset of YAML. But the subset supported
contains most of the features for the more common usese of YAML.
SYNOPSIS
#############################################
# In your file
---
rootproperty: blah
section:
one: two
three: four
Foo: Bar
empty: ~
#############################################
# In your program
use YAML::Tiny;
# Create a YAML file
my $yaml = YAML::Tiny->new;
# Open the config
$yaml = YAML::Tiny->read( 'file.yml' );
# Reading properties
my $root = $yaml->[0]->{rootproperty};
my $one = $yaml->[0]->{section}->{one};
my $Foo = $yaml->[0]->{section}->{Foo};
# Changing data
$yaml->[0]->{newsection} = { this => 'that' }; # Add a section
$yaml->[0]->{section}->{Foo} = 'Not Bar!'; # Change a value
delete $yaml->[0]->{section}; # Delete a value
# Add an entire document
$yaml->[1] = [ 'foo', 'bar', 'baz' ];
# Save the file
$yaml->write( 'file.conf' );
DESCRIPTION
YAML::Tiny is a perl class for reading and writing YAML-style files,
written with as little code as possible, reducing load time and memory
overhead.
Most of the time it is accepted that Perl applications use a lot of
memory and modules. The ::Tiny family of modules is specifically
intended to provide an ultralight and zero-dependency alternative to
many more-thorough standard modules.
This module is primarily for reading human-written files (like simple
config files) and generating very simple human-readable files. Note that
I said human-readable and not geek-readable. The sort of files that your
average manager or secretary should be able to look at and make sense
of.
YAML::Tiny does not generate comments, it won't necesarily preserve the
order of your hashes, and it will normalise if reading in and writing
out again.
It only supports a very basic subset of the full YAML specification.
Usage is targetted at files like Perl's META.yml, for which a small and
easily-embeddable module is extremely attractive.
Features will only be added if they are human readable, and can be
written in a few lines of code. Please don't be offended if your request
is refused. Someone has to draw the line, and for YAML::Tiny that
someone is me.
If you need something with more power move up to YAML (4 megabytes of
memory overhead) or YAML::Syck (275k, but requires libsyck and a C
compiler).
To restate, YAML::Tiny does not preserve your comments, whitespace, or
the order of your YAML data. But it should round-trip from Perl
structure to file and back again just fine.
YAML TINY SPECIFICATION
This section of the documentation provides a specification for "YAML
Tiny", a subset of the YAML specification.
It is based on and described comparatively to the YAML 1.1 Working Draft
2004-12-28 specification, located at
<http://yaml.org/spec/current.html>.
Terminology and chapter numbers are based on that specification.
1. Introduction and Goals
The purpose of the YAML Tiny specification is to describe a useful
subset of the YAML specification that can be used for typical
document-oriented use cases such as configuration files and simple data
structure dumps.
Many specification elements that add flexibility or extensibility are
intentionally removed, as is support for complex datastructures, class
and object-orientation.
In general, the YAML Tiny language targets only those data structures
available in JSON, with the additional limitation that only simple keys
are supported.
As a result, all possible YAML Tiny documents should be able to be
transformed into an equivalent JSON document, although the reverse is
not necesarily true (but will be true in simple cases).
As a result of these simplifications the YAML Tiny specification should
be implementable in a (relatively) small amount of code in any language
that supports Perl Compatible Regular Expressions (PCRE).
2. Introduction
YAML Tiny supports three data structures. These are scalars (in a
variety of forms), block-form sequences and block-form mappings.
Flow-style sequences and mappings are not supported, with some minor
exceptions detailed later.
The use of three dashes "---" to indicate the start of a new document is
supported, and multiple documents per file/stream is allowed.
Both line and inline comments are supported.
Scalars are supported via the plain style, single quote and double
quote, as well as literal-style and folded-style multi-line scalars.
The use of explicit tags is not supported.
The use of "null" type scalars is supported via the ~ character.
The use of "bool" type scalars is not supported.
However, serializer implementations should take care to explicitly
escape strings that match a "bool" keyword in the following set to
prevent other implementations that do support "bool" accidentally
reading a string as a boolean
y|Y|yes|Yes|YES|n|N|no|No|NO
|true|True|TRUE|false|False|FALSE
|on|On|ON|off|Off|OFF
The use of anchors and aliases is not supported.
The use of directives is supported only for the %YAML directive.
3. Processing YAML Tiny Information
Processes
The YAML specification dictates three-phase serialization and
three-phase deserialization.
The YAML Tiny specification does not mandate any particular methodology
or mechanism for parsing.
Any compliant parser is only required to parse a single document at a
time. The ability to support streaming documents is optional and most
likely non-typical.
Because anchors and aliases are not supported, the resulting
representation graph is thus directed but (unlike the main YAML
specification) acyclic.
Circular references/pointers are not possible, and any YAML Tiny
serializer detecting a circular reference should error with an
appropriate message.
Presentation Stream
YAML Tiny is notionally unicode, but support for unicode is required if
the underlying language or system being used to implement a parser does
not support Unicode. If unicode is encountered in this case an error
should be returned.
Loading Failure Points
YAML Tiny parsers and emitters are not expected to recover from adapt to
errors. The specific error modality of any implementation is not
dictated (return codes, exceptions, etc) but is expected to be
consistant.
4. Syntax
Character Set
YAML Tiny streams are implemented primarily using the ASCII character
set, although the use of Unicode inside strings is allowed if support by
the implementation.
Specific YAML Tiny encoded document types aiming for maximum
compatibility should restrict themselves to ASCII.
The escaping and unescaping of the 8-bit YAML escapes is required.
The escaping and unescaping of 16-bit and 32-bit YAML escapes is not
required.
Indicator Characters
Support for the "~" null/undefined indicator is required.
Implementations may represent this as appropriate for the underlying
language.
Support for the "-" block sequence indicator is required.
Support for the "?" mapping key indicator is not required.
Support for the ":" mapping value indicator is required.
Support for the "," flow collection indicator is not required.
Support for the "[" flow sequence indicator is not required, with one
exception (detailed below).
Support for the "]" flow sequence indicator is not required, with one
exception (detailed below).
Support for the "{" flow mapping indicator is not required, with one
exception (detailed below).
Support for the "}" flow mapping indicator is not required, with one
exception (detailed below).
Support for the "#" comment indicator is required.
Support for the "&" anchor indicator is not required.
Support for the "*" alias indicator is not required.
Support for the "!" tag indicator is not required.
Support for the "|" literal block indicator is required.
Support for the ">" folded block indicator is required.
Support for the "'" single quote indicator is required.
Support for the """ double quote indicator is required.
Support for the "%" directive indicator is required, but only for the
special case of a %YAML version directive before the "---" document
header, or on the same line as the document header.
For example:
%YAML 1.1
---
- A sequence with a single element
Special Exception:
To provide the ability to support empty sequences and mappings, support
for the constructs [] (empty sequence) and {} (empty mapping) are
required.
For example,
%YAML 1.1
# A document consisting of only an empty mapping
--- {}
# A document consisting of only an empty sequence
--- []
# A document consisting of an empty mapping within a sequence
- foo
- {}
- bar
Syntax Primitives
Other than the empty sequence and mapping cases described above, YAML
Tiny supports only the indentation-based block-style group of contexts.
All five scalar contexts are supported.
Indentation spaces work as per the YAML specification in all cases.
Comments work as per the YAML specification in all simple cases. Support
for indented multi-line comments is not required.
Seperation spaces work as per the YAML specification in all cases.
YAML Tiny Character Stream
The only directive supported by the YAML Tiny specification is the %YAML
language/version identifier. Although detected, this directive will have
no control over the parsing itself.
The parser must recognise both the YAML 1.0 and YAML 1.1+ formatting of
this directive (as well as the commented form, although no explicit code
should be needed to deal with this case, being a comment anyway)
That is, all of the following should be supported.
--- #YAML:1.0
- foo
%YAML:1.0
---
- foo
% YAML 1.1
---
- foo
Support for the %TAG directive is not required.
Support for additional directives is not required.
Support for the document boundary marker "---" is required.
Support for the document boundary market "..." is not required.
If necesary, a document boundary should simply by indicated with a "---"
marker, with not preceding "..." marker.
Support for empty streams (containing no documents) is required.
Support for implicit document starts is required.
That is, the following must be equivalent.
# Full form
%YAML 1.1
---
foo: bar
# Implicit form
foo: bar
Nodes
Support for nodes optional anchor and tag properties are not required.
Support for node anchors is not required.
Support for node tags is not required.
Support for alias nodes is not required.
Support for flow nodes is not required.
Support for block nodes is required.
Scalar Styles
Support for all five scalar styles are required as per the YAML
specification, although support for quoted scalars spanning more than
one line is not required.
Support for the chomping indicators on multi-line scalar styles is
required.
Collection Styles
Support for block-style sequences is required.
Support for flow-style sequences is not required.
Support for block-style mappings is required.
Support for flow-style mappings is not required.
Both sequences and mappings should be able to be arbitrarily nested.
Support for plain-style mapping keys is required.
Support for quoted keys in mappings is not required.
Support for "?"-indicated explicit keys is not required.
Here endeth the specification.
Additional Perl-Specific Notes
For some Perl applications, it's important to know if you really have a
number and not a string.
That is, in some contexts is important that 3 the number is distinctive
from "3" the string.
Because even Perl itself is not trivially able to understand the
difference (certainly without XS-based modules) Perl implementations of
the YAML Tiny specification are not required to retain the
distinctiveness of 3 vs "3".
METHODS
new
The constructor "new" creates and returns an empty "YAML::Tiny" object.
read $filename
The "read" constructor reads a YAML file from a file name, and returns a
new "YAML::Tiny" object containing the parsed content.
Returns the object on success, or "undef" on error.
When "read" fails, "YAML::Tiny" sets an error message internally you can
recover via "YAML::Tiny->errstr". Although in some cases a failed "read"
will also set the operating system error variable $!, not all errors do
and you should not rely on using the $! variable.
read_string $string;
The "read" constructor reads a YAML file from a file name, and returns a
new "YAML::Tiny" object containing the parsed content.
Returns the object on success, or "undef" on error.
write $filename
The "write" method generates the file content for the properties, and
writes it to disk to the filename specified.
Returns true on success or "undef" on error.
write_string
Generates the file content for the object and returns it as a string.
errstr
When an error occurs, you can retrieve the error message either from the
$YAML::Tiny::errstr variable, or using the "errstr()" method.
FUNCTIONS
YAML::Tiny implements a number of functions to add compatibility with
the YAML API. These should be a drop-in replacement, except that
YAML::Tiny will not export functions by default, and so you will need to
explicitly import the functions.
Dump
my $string = 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
my @documents = 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.
freeze() and thaw()
Aliases to Dump() and Load() for Storable fans. This will also allow
YAML::Tiny 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.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=YAML-Tiny>
AUTHOR
Adam Kennedy <adamk@cpan.org>
SEE ALSO
YAML, YAML::Syck, Config::Tiny, CSS::Tiny,
<http://use.perl.org/~Alias/journal/29427>, <http://ali.as/>
COPYRIGHT
Copyright 2006 - 2012 Adam Kennedy.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included
with this module.