Use placeholders in yaml

Question

Is there a way to use placeholders in yaml like this:

foo: &FOO
    <<propname>>: 
        type: number 
        default: <<default>>

bar:
    - *FOO 
       propname: "some_prop"
       default: "some default"

This question is related to yaml computed-properties indirection template-variables

User · Answer

With Yglu Structural Templating  your example can be written   foo             propname        type  number       default       default  bar     apply  foo       propname   some prop      default   some default    Disclaimer  I am the author or Yglu

User · Answer

I suppose https   get-ytt io  would be an acceptable solution to your problem

User · Answer

Context  YAML version 1 2 user wishes to  include variable placeholders in YAML have placeholders replaced with computed values  upon yaml load be able to use placeholders for both YAML mapping keys and values    Problem  YAML does not natively support variable placeholders  Anchors and Aliases almost provide the desired functionality  but these do not work as variable placeholders that can be inserted into arbitrary regions throughout the YAML text  They must be placed as separate YAML nodes  There are some add-on libraries that support arbitrary variable placeholders  but they are not part of the native YAML specification   Example Consider the following example YAML  It is well-formed YAML syntax  however it uses  non-standard  curly-brace placeholders with embedded expressions  The embedded expressions do not produce the desired result in YAML  because they are not part of the native YAML specification  Nevertheless  they are used in this example only to help illustrate what is available with standard YAML and what is not  part01 customer info    cust fname     quot Homer quot    cust lname     quot Himpson quot    cust motto     quot I love donuts  quot    cust email    homer himpson org  part01 government info    govt sales taxrate  1 15  part01 purchase info    prch unit label      quot Bacon-Wrapped Fancy Glazed Donut quot    prch unit price     3 00   prch unit quant     7   prch product cost    quot   prch unit price   prch unit quant   quot    prch total cost      quot   prch product cost   govt sales taxrate   quot      part02 shipping info    cust fname     quot   cust fname   quot    cust lname     quot   cust lname   quot    ship city     Houston   ship state    Hexas      part03 email info    cust email       quot   cust email   quot    mail subject    Thanks for your DoughNutz order    mail notes        We want the mail greeting to have all the expected values     with filled-in placeholders  and not curly-braces     mail greeting        Greetings   cust fname     cust lname             We love your motto  quot   cust motto   quot  and we agree with you           Your total purchase price is   prch total cost         Explanation  The substitutions marked in GREEN are readily available in standard YAML  using anchors  aliases  and merge keys   The substitutions marked in YELLOW are technically available in standard YAML  but not without a custom type declaration  or some other binding mechanism   The substitutions marked in RED are not available in standard YAML  Yet there are workarounds and alternatives  such as through string formatting or string template engines  such as python s str format      Details A frequently-requested feature for YAML is the ability to insert arbitrary variable placeholders that support arbitrary cross-references and expressions that relate to the other content in the same  or transcluded  YAML file s   YAML supports anchors and aliases  but this feature does not support arbitrary placement of placeholders and expressions anywhere in the YAML text  They only work with YAML nodes  YAML also supports custom type declarations  however these are less common  and there are security implications if you accept YAML content from potentially untrusted sources  YAML addon libraries There are YAML extension libraries  but these are not part of the native YAML spec   Ansible  https   docs ansible com ansible-container container yml template html  supports many extensions to YAML  however it is an Orchestration tool  which is overkill if you just want YAML    https   github com kblomqvist yasha https   bitbucket org djarvis yamlp  Workarounds  Use YAML in conjunction with a template system  such as Jinja2 or Twig Use a YAML extension library Use sprintf or str format style functionality from the hosting language  Alternatives  YTT YAML Templating essentially a fork of YAML with additional features that may be closer to the goal specified in the OP  Jsonnet shares some similarity with YAML  but with additional features that may be closer to the goal specified in the OP   See also Here at SO  YAML variables in config files Load YAML nested with Jinja2 in Python String interpolation in YAML how to reference a YAML  quot setting quot  from elsewhere in the same YAML file  Use YAML with variables How can I include a YAML file inside another  Passing variables inside rails internationalization yml file Can one YAML object refer to another  is there a way to reference a constant in a yaml with rails  YAML with nested Jinja YAML merge keys YAML merge keys  Outside SO  https   learnxinyminutes com docs yaml  https   github com dreftymac awesome-yaml variables https   duckduckgo com  q yaml variables in config file amp t h  amp ia web

[yaml] Use placeholders in yaml

The answer is

Examples related to yaml

Examples related to computed-properties

Examples related to indirection

Examples related to template-variables

Tags