How to dump strings in YAML using literal scalar style?

Question

I have a big string of formatted data (e.g. JSON) that I want to dump to YAML using Psych in ruby while preserving formatting.

Basically, I want for JSON to appear in YAML using literal style:

---
json: |
  {
    "page": 1,
    "results": [
      "item", "another"
    ],
    "total_pages": 0
  }

However, when I use YAML.dump it doesn't use literal style. I get something like this:

---
json: ! "{\n  \"page\": 1,\n  \"results\": [\n    \"item\", \"another\"\n  ],\n  \"total_pages\":
  0\n}\n"

How can I tell Psych to dump scalars in wanted style?

---

Solution:

Big thanks to Aaron Patterson for his solution that I'm expanding on here: https://gist.github.com/2023978

Although a bit verbose, that gist is a working way of tagging certain strings in ruby to be output using literal style in YAML.

Answer 1

require 'psych'

# Construct an AST
visitor = Psych::Visitors::YAMLTree.new({})
visitor << DATA.read
ast = visitor.tree

# Find all scalars and modify their formatting
ast.grep(Psych::Nodes::Scalar).each do |node|
  node.plain  = false
  node.quoted = true
  node.style  = Psych::Nodes::Scalar::LITERAL
end

begin
  # Call the `yaml` method on the ast to convert to yaml
  puts ast.yaml
rescue
  # The `yaml` method was introduced in later versions, so fall back to
  # constructing a visitor
  Psych::Visitors::Emitter.new($stdout).accept ast
end

__END__
{
  "page": 1,
  "results": [
    "item", "another"
],
  "total_pages": 0
}