Module: Psych

Dump Ruby object o to a YAML string. Optional options may be passed in to control the output format. If an IO object is passed in, the YAML will be dumped to that IO object.

Currently supported options are:

:indentation

Number of space characters used to indent. Acceptable value should be in 0..9 range, otherwise option is ignored.

Default: 2.

:line_width

Max character to wrap line at.

Default: 0 (meaning “wrap at 81”).

:canonical

Write “canonical” YAML form (very verbose, yet strictly formal).

Default: false.

:header

Write %YAML [version] at the beginning of document.

Default: false.

Example:

# Dump an array, get back a YAML string
Psych.dump(['a', 'b'])  # => "---\n- a\n- b\n"

# Dump an array to an IO object
Psych.dump(['a', 'b'], StringIO.new)  # => #<StringIO:0x000001009d0890>

# Dump an array with indentation set
Psych.dump(['a', ['b']], indentation: 3) # => "---\n- a\n-  - b\n"

# Dump an array to an IO with indentation set
Psych.dump(['a', ['b']], StringIO.new, indentation: 3)

Dump a list of objects as separate documents to a document stream.

Example:

Psych.dump_stream("foo\n  ", {}) # => "--- ! \"foo\\n  \"\n--- {}\n"

Returns the version of libyaml being used

Load yaml in to a Ruby data structure. If multiple documents are provided, the object contained in the first document will be returned. filename will be used in the exception message if any exception is raised while parsing. If yaml is empty, it returns the specified fallback return value, which defaults to false.

Raises a ::Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.load("--- a")             # => 'a'
Psych.load("---\n - a\n - b")   # => ['a', 'b']

begin
  Psych.load("--- `", filename: "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

When the optional symbolize_names keyword argument is set to a true value, returns symbols for keys in Hash objects (default: strings).

Psych.load("---\n foo: bar")                         # => {"foo"=>"bar"}
Psych.load("---\n foo: bar", symbolize_names: true)  # => {:foo=>"bar"}

Raises a TypeError when yaml parameter is NilClass. This method is similar to .safe_load except that Symbol objects are allowed by default.

Loads the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to false. See load for options.

Load multiple documents given in yaml. Returns the parsed documents as a list. If a block is given, each document will be converted to Ruby and passed to the block during parsing

Example:

Psych.load_stream("--- foo\n...\n--- bar\n...") # => ['foo', 'bar']

list = []
Psych.load_stream("--- foo\n...\n--- bar\n...") do |ruby|
  list << ruby
end
list # => ['foo', 'bar']

Parse a YAML string in yaml. Returns the ::Psych::Nodes::Document. filename is used in the exception message if a ::Psych::SyntaxError is raised.

Raises a ::Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.parse("---\n - a\n - b") # => #<Psych::Nodes::Document:0x00>

begin
  Psych.parse("--- `", filename: "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

See ::Psych::Nodes for more information about YAML AST.

Parse a file at filename. Returns the ::Psych::Nodes::Document.

Raises a ::Psych::SyntaxError when a YAML syntax error is detected.

Parse a YAML string in yaml. Returns the ::Psych::Nodes::Stream. This method can handle multiple YAML documents contained in yaml. filename is used in the exception message if a ::Psych::SyntaxError is raised.

If a block is given, a ::Psych::Nodes::Document node will be yielded to the block as it’s being parsed.

Raises a ::Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.parse_stream("---\n - a\n - b") # => #<Psych::Nodes::Stream:0x00>

Psych.parse_stream("--- a\n--- b") do |node|
  node # => #<Psych::Nodes::Document:0x00>
end

begin
  Psych.parse_stream("--- `", filename: "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

Raises a TypeError when NilClass is passed.

See ::Psych::Nodes for more information about YAML AST.

Returns a default parser

Safely dump Ruby object o to a YAML string. Optional options may be passed in to control the output format. If an IO object is passed in, the YAML will be dumped to that IO object. By default, only the following classes are allowed to be serialized:

• TrueClass

• FalseClass

• NilClass

• Integer

• Float

• String

• Array

• Hash

Arbitrary classes can be allowed by adding those classes to the permitted_classes keyword argument. They are additive. For example, to allow Date serialization:

Psych.safe_dump(yaml, permitted_classes: [Date])

Now the Date class can be dumped in addition to the classes listed above.

A ::Psych::DisallowedClass exception will be raised if the object contains a class that isn’t in the permitted_classes list.

Currently supported options are:

:indentation

Number of space characters used to indent. Acceptable value should be in 0..9 range, otherwise option is ignored.

Default: 2.

:line_width

Max character to wrap line at.

Default: 0 (meaning “wrap at 81”).

:canonical

Write “canonical” YAML form (very verbose, yet strictly formal).

Default: false.

:header

Write %YAML [version] at the beginning of document.

Default: false.

Example:

# Dump an array, get back a YAML string
Psych.safe_dump(['a', 'b'])  # => "---\n- a\n- b\n"

# Dump an array to an IO object
Psych.safe_dump(['a', 'b'], StringIO.new)  # => #<StringIO:0x000001009d0890>

# Dump an array with indentation set
Psych.safe_dump(['a', ['b']], indentation: 3) # => "---\n- a\n-  - b\n"

# Dump an array to an IO with indentation set
Psych.safe_dump(['a', ['b']], StringIO.new, indentation: 3)

Safely load the yaml string in yaml. By default, only the following classes are allowed to be deserialized:

• TrueClass

• FalseClass

• NilClass

• Integer

• Float

• String

• Array

• Hash

Recursive data structures are not allowed by default. Arbitrary classes can be allowed by adding those classes to the permitted_classes keyword argument. They are additive. For example, to allow Date deserialization:

Psych.safe_load(yaml, permitted_classes: [Date])

Now the Date class can be loaded in addition to the classes listed above.

Aliases can be explicitly allowed by changing the aliases keyword argument. For example:

x = []
x << x
yaml = Psych.dump x
Psych.safe_load yaml               # => raises an exception
Psych.safe_load yaml, aliases: true # => loads the aliases

A ::Psych::DisallowedClass exception will be raised if the yaml contains a class that isn’t in the permitted_classes list.

A ::Psych::BadAlias exception will be raised if the yaml contains aliases but the aliases keyword argument is set to false.

filename will be used in the exception message if any exception is raised while parsing.

When the optional symbolize_names keyword argument is set to a true value, returns symbols for keys in Hash objects (default: strings).

Psych.safe_load("---\n foo: bar")                         # => {"foo"=>"bar"}
Psych.safe_load("---\n foo: bar", symbolize_names: true)  # => {:foo=>"bar"}

Safely loads the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to false. See safe_load for options.

Dump Ruby object to a ::Psych::JSON string.

Load yaml in to a Ruby data structure. If multiple documents are provided, the object contained in the first document will be returned. filename will be used in the exception message if any exception is raised while parsing. If yaml is empty, it returns the specified fallback return value, which defaults to false.

Raises a ::Psych::SyntaxError when a YAML syntax error is detected.

Example:

Psych.unsafe_load("--- a")             # => 'a'
Psych.unsafe_load("---\n - a\n - b")   # => ['a', 'b']

begin
  Psych.unsafe_load("--- `", filename: "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(file.txt): found character that cannot start any token"
end

When the optional symbolize_names keyword argument is set to a true value, returns symbols for keys in Hash objects (default: strings).

Psych.unsafe_load("---\n foo: bar")                         # => {"foo"=>"bar"}
Psych.unsafe_load("---\n foo: bar", symbolize_names: true)  # => {:foo=>"bar"}

Raises a TypeError when yaml parameter is NilClass

NOTE: This method *should not* be used to parse untrusted documents, such as YAML documents that are supplied via user input. Instead, please use the load method or the safe_load method.

Load the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to false.

NOTE: This method *should not* be used to parse untrusted documents, such as YAML documents that are supplied via user input. Instead, please use the safe_load_file method.

Workaround for emulating warn '...', uplevel: 1 in Ruby 2.4 or lower.