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yglu ReadMe

Yglu ᕄ !?

Build Status PyPI version

* Try Yglu Online *

Yglu is YAML augmented with an advanced expression language. Unlike usual text templating, Yglu relies on the YAML structure and leverages its tag system combined with the YAQL query language.

This association enables templating and functional processing a bit like if YAML nodes were spreadsheet cells.

Yglu input documents are pure and valid YAML using tags for computed nodes.

input 
a: 1
b: !? .a + 1
!if .b = 2:
  c: 3
output 
a: 1
b: 2
c: 3
input 
names: !-
  - 'nginx:1.16'
  - 'node:13.6'
  - 'couchbase:9.3'
image: !()
  !? $.split(':')[0]:
    version: !? $.split(':')[1]
images: !?
  $_.names
    .select(($_.image)($))
    .aggregate($1.mergeWith($2), {})
 output 
images:
  nginx:
    version: '1.16'
  node:
    version: '13.6'
  couchbase:
    version: '9.3'
     
     
     
     

In the example above, the names sequence is hidden, image is a function (like a template block) and images is an expression which iterates through all names, applies the image function to each one and aggregates the individual results by merging them together as a mapping.

As such an operation is often needed, Yglu provides a !for tag for merging a sequence iterated over a function:

input 
names: !-
  - 'nginx:1.16'
  - 'node:13.6'
  - 'couchbase:9.3'
images:
  !for .names: !()
    !? $.split(':')[0]:
      version: !? $.split(':')[1]
 output 
images:
  nginx:
    version: '1.16'
  node:
    version: '13.6'
  couchbase:
    version: '9.3'
     

See the test samples for more examples.

* Try Yglu Online *

Install

pip3 install yglu

Run

Usage: yglu [options] [<filename>]

Options:
  -v - -version          Print version and exit.
  -h - -help             Print help and exit.

Tags

Tags specify an alteration of the document structure.

Tag    Description
!? Evaluate an expression. The result can be a scalar, mapping or sequence. Can also be used in mapping keys.
!- Hide the node in the output but keep it accessible from expressions. Can be an expression.
!() Make the node reusable in expressions as a function.
!if Conditional merge. See if.yml.
!for Merge the results of a function applied to all items of a sequence . See for.yml.
!apply Apply a function or function block to a block. See function.yml.

Expressions

Expressions are written in YAQL.

They are evaluated in a context with the following variables defined:

Variable Description
$_ Refers to the current document root. Can be omitted at the beginning of the expression if it starts with a dot.
$ Implicit argument of functions.
$env Gives access to environment variables. Disabled by default. Set the $YGLU_ENABLE_ENV environment variable to enable this feature.
$this Refers to the current function block node in order to access its children nodes. See function.yml

Built-in Functions

In addition to the standard YAQL library, Yglu defines the following functions:

Function Description
$import(filename) Imports another document in the current node. By default, it is only permitted to import files from within the directory hierarchy of the input file. Set $YGLU_IMPORT_ALLOW to a list of permitted directories.