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Bryan Woolsey
Bryan Woolsey

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Dealing with long strings in YAML

#puppet #yaml #hiera #ruby

We have a step in our Puppet CI/CD Pipeline that lints YAML data using adrienverge/yamllint. One of the rules limits the number of characters on a single line. Normally not a huge deal... except when dealing with long URIs or other long strings.

The problem is, I have to change URI Hiera data so infrequently that I always forget exactly what the syntax is. Admittedly, this post is really for me to look back on and reference, but why not share?

And while we're on the topic:

  • YAML Cookbook for Ruby is an awesome resource for YAML syntax in general.
  • Puppet parses YAML using the following function in Ruby: 
 YAML.safe_load(File.read(path), [Symbol], [], true)
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Combine with Interactive Ruby Shell or ruby -e for a quick and easy way to test any YAML file you create.

Plain Style

"Flow" Styles

No character escaping, or characters matching /[#:]/.

--- key: This is a very long string.
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{ "key" => "This is a very long string." }
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Single-quoted style

No special characters, no escaping. Literal ' must be doubled-up ('').

--- key: 'This isn''t a very short string.'
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{ "key" => "This isn't a very short string." }
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Double-quoted style

Characters matching /[\\"]/ must be escaped by a \ character. Common escape sequences may be used. Line concatenation with a trailing \.

VERY useful for long URIs.

--- key: "http://this.is.my\  .very.long.string"
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{ "key" => "http://this.is.my.very.long.string" }
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Block Notation

Literal Style 

--- key: | This is a very long string.
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{ "key" => "This is a very\nlong string.\n" }
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Folded Style 

--- key: > This is a very long string.
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{ "key" => "This is a very long string.\n" }
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Block chomping indicator

You may notice that both strings have newlines attached to the end. Want those gone? Use a different chomping indicator:

  • |, >: "clip". Keeps the newline.
  • |+, >+: "keep". Keeps the newline, and also keeps tailing blank lines.
  • |-, >-: "strip". Removes the newline. 
--- key0: > Do. Or do not. There is no try. key1: >+ I find your lack of faith disturbing. key2: >- The Force will be with you. Always.
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{ "key0" => "Do. Or do not. There is no try.\n", "key1" => "I find your lack of faith disturbing.\n\n", "key2" => "The Force will be with you. Always." }
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Source: YAML v1.2 Specification

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