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https://github.com/juliojimenez/yamler

YAML Parsing GitHub Action
https://github.com/juliojimenez/yamler

github-actions github-pages jekyll markdown-frontmatter typescript yaml yaml-parser yamler

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YAML Parsing GitHub Action

Awesome Lists containing this project

README 

        
[![yamler Tests](https://github.com/juliojimenez/yamler/actions/workflows/tests.yml/badge.svg)](https://github.com/juliojimenez/yamler/actions/workflows/tests.yml) [![yamler Test Job](https://github.com/juliojimenez/yamler/actions/workflows/main.yml/badge.svg)](https://github.com/juliojimenez/yamler/actions/workflows/main.yml) ![GitHub release (with filter)](https://img.shields.io/github/v/release/juliojimenez/yamler)



# yamler



- [Usage](#usage)

- [Output](#output)

- [Accessing Output Variables](#accessing-output-variables)

- [GitHub Pages (Jekyll) Front Matter](#github-pages-jekyll-front-matter)



**yamler** is a GitHub Action that parses an entire YAML document and makes all elements available as GitHub Workflow output variables.



Support for multiple documents is provided by the `multidoc` attribute (default: `false`).



> YAML uses three dashes (`---`) to separate directives from document content. This also serves to signal the start of a document if no directives are present. (https://yaml.org/spec/1.2.2/#22-structures)



## Usage



```

- name: yamler

  uses: juliojimenez/[email protected]

  id: yamler

  with:

    yaml-file: "example.yaml"

    multidoc: true|false

```



## Output



yamler outputs the entire document as _yamler-formatted_ output variable names. This serves as a good reference when the YAML document contains tags with characters not supported by GitHub Workflow variable names. yamler will automatically transform tags into friendly variable names.



In this example, the test file used is derived from [yaml.org](https://yaml.org). A deeper _number_ array was added to test for types other than string, object, and array.



```

***** Output Variables *****

yaml

what_it_is

yaml_resources__yaml_1_2_3rd_edition

yaml_resources__yaml_1_1_2nd_edition

yaml_resources__yaml_1_0_1st_edition

yaml_resources__yaml_issues_page

yaml_resources__yaml_mailing_list

yaml_resources__yaml_irc_channel

yaml_resources__yaml_cookbook_ruby

yaml_resources__yaml_reference_parser

projects__c_cpp_libraries__0

projects__c_cpp_libraries__1

projects__c_cpp_libraries__2

projects__ruby__0

projects__ruby__1

projects__ruby__2

projects__python__0

projects__python__1

projects__java__0

projects__java__1

projects__java__2

projects__java__3

projects__perl_modules__0

projects__perl_modules__1

projects__perl_modules__2

projects__perl_modules__3

projects__perl_modules__4

projects__cs__net__0

projects__cs__net__1

projects__php__0

projects__php__1

projects__php__2

projects__ocaml__0

projects__javascript__0

projects__javascript__1

projects__actionscript__0

projects__haskell__0

projects__others__0

related_projects__0

related_projects__1

related_projects__2

related_projects__3

related_projects__4

related_projects__5

number_object__number_sub_object__number_sub_sub_array__0

number_object__number_sub_object__number_sub_sub_array__1

number_object__number_sub_object__number_sub_sub_array__2

news__0

news__1

news__2

news__3

news__4

news__5

news__6

news__7

news__8

news__9

news__10

news__11

news__12

news__13

news__14

news__15

news__16

news__17

news__18

news__19

news__20

news__21

news__22

news__23

news__24

news__25

news__26

news__27

news__28

news__29

news__30

news__31

news__32

news__33

news__34

news__35

news__36

news__37

```



Multiple documents are zero-indexed and variable names are prefixed with `docN`. Formatting for the rest of the variable name remains the same as above.



```

***** Output Variables *****

doc0__name

doc0__purpose

doc1__yaml

doc1__what_it_is

doc1__yaml_resources__yaml_1_2_3rd_edition

doc1__yaml_resources__yaml_1_1_2nd_edition

doc1__yaml_resources__yaml_1_0_1st_edition

doc1__yaml_resources__yaml_issues_page

doc1__yaml_resources__yaml_mailing_list

doc1__yaml_resources__yaml_irc_channel

doc1__yaml_resources__yaml_cookbook_ruby

doc1__yaml_resources__yaml_reference_parser

doc1__projects__c_cpp_libraries__0

doc1__projects__c_cpp_libraries__1

doc1__projects__c_cpp_libraries__2

doc1__projects__ruby__0

doc1__projects__ruby__1

doc1__projects__ruby__2

doc1__projects__python__0

doc1__projects__python__1

doc1__projects__java__0

doc1__projects__java__1

doc1__projects__java__2

doc1__projects__java__3

doc1__projects__perl_modules__0

doc1__projects__perl_modules__1

doc1__projects__perl_modules__2

doc1__projects__perl_modules__3

doc1__projects__perl_modules__4

doc1__projects__cs__net__0

doc1__projects__cs__net__1

doc1__projects__php__0

doc1__projects__php__1

doc1__projects__php__2

doc1__projects__ocaml__0

doc1__projects__javascript__0

doc1__projects__javascript__1

doc1__projects__actionscript__0

doc1__projects__haskell__0

doc1__projects__others__0

doc1__related_projects__0

doc1__related_projects__1

doc1__related_projects__2

doc1__related_projects__3

doc1__related_projects__4

doc1__related_projects__5

doc1__number_object__number_sub_object__number_sub_sub_array__0

doc1__number_object__number_sub_object__number_sub_sub_array__1

doc1__number_object__number_sub_object__number_sub_sub_array__2

doc1__news__0

doc1__news__1

doc1__news__2

doc1__news__3

doc1__news__4

doc1__news__5

doc1__news__6

doc1__news__7

doc1__news__8

doc1__news__9

doc1__news__10

doc1__news__11

doc1__news__12

doc1__news__13

doc1__news__14

doc1__news__15

doc1__news__16

doc1__news__17

doc1__news__18

doc1__news__19

doc1__news__20

doc1__news__21

doc1__news__22

doc1__news__23

doc1__news__24

doc1__news__25

doc1__news__26

doc1__news__27

doc1__news__28

doc1__news__29

doc1__news__30

doc1__news__31

doc1__news__32

doc1__news__33

doc1__news__34

doc1__news__35

doc1__news__36

doc1__news__37

```



## Accessing Output Variables



yamler preserves document structure using double-underscore (\_\_) notation. If a value is located at `foo.bar`, the yamler output variable will become `foo__bar`. Arrays are indexed in a similar way, the element `bar.foo[5]`can be accessed with yamler at`bar__foo__5`.



```

# Use the output from the yamler step

- name: Output Test

  run: |

    echo "${{ steps.yamler.outputs.yaml }}"

    echo "${{ steps.yamler.outputs.what_it_is }}"

    echo "${{ steps.yamler.outputs.yaml_resources__yaml_1_2_3rd_edition }}"

```



In a multidoc scenario...



```

# Use the output from the yamler step

- name: Output Test

  run: |

    echo "${{ steps.yamler.outputs.doc0__name }}"

    echo "${{ steps.yamler.outputs.doc0__purpose }}"

```



## GitHub Pages (Jekyll) Front Matter



yamler can be used to parse YAML front matter in GitHub Pages (Jekyll) markdown files. The front matter must be the first thing in the file and must take the form of valid YAML set between triple-dashed lines. Here is a basic example:



```yaml

---

title: Front Matter

permalink: /docs/front-matter/

redirect_from: /docs/frontmatter/index.html

reviewed_on: 2025-07-07

reviewed_by: juliojimenez

---



# Example



Blah blah blah

```



Here is an example of how to use yamler to parse the front matter from a markdown file:



```yaml

- name: yamler

  uses: juliojimenez/[email protected]

  id: yamler

  with:

    yaml-file: "doc.md"

    multidoc: true



- name: Output

  run: |

    echo "${{ steps.yamler.outputs.doc0__title }}"

    echo "${{ steps.yamler.outputs.doc0__permalink }}"

    echo "${{ steps.yamler.outputs.doc0__redirect_from }}"

    echo "${{ steps.yamler.outputs.doc0__reviewed_on }}"

    echo "${{ steps.yamler.outputs.doc0__reviewed_by }}"

```



```

Front Matter

/docs/front-matter/

/docs/frontmatter/index.html

2024-07-07

juliojimenez

```



This is a great way to validate front matter attributes in markdown files and make it available for further processing in GitHub Workflows. For example:



- Ensuring all markdown files have a set of required attributes.

- Listing documents that have not been reviewed in a while.

- Notifying authors when their documents are out of date.