yamler
yamler
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. 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 atbar__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 "${{ steps.yamler.outputs.doc0__purpose }}"
GitHub Pages (Jekyll) Front Matter
yamler can be used to parse YAML front matter in GitHub Pages (Jekyll) markdown files. The front matter must be the first thing in the file and must take the form of valid YAML set between triple-dashed lines. Here is a basic example:
---
title: Front Matter
permalink: /docs/front-matter/
redirect_from: /docs/frontmatter/index.html
reviewed_on: 2025-07-07
reviewed_by: juliojimenez
---
# Example
Blah blah blah
Here is an example of how to use yamler to parse the front matter from a markdown file:
- name: yamler
uses: juliojimenez/[email protected]
id: yamler
with:
yaml-file: "doc.md"
multidoc: true
- name: Output
run: |
echo "${{ 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.