Convert between XML and JSON

Goal: Turn an XML file into JSON, reshape it into the plain records you actually want, and write JSON (or a modified tree) back out as XML.

Prerequisites: The built-in xml module for reshaping and writing trees. Plain conversion needs no import: -I xml reads XML and -F xml writes it.

Query

XML to a plain JSON array:

$ mq -I xml -F json 'import "xml" | xml::xml_find_all("book") | map(fn(b): {"id": xml::xml_attr(b, "id"), "title": xml::xml_text(xml::xml_find(b, "title")), "year": to_number(xml::xml_text(xml::xml_find(b, "year")))};)' books.xml

JSON to XML:

$ echo '{"name": "web", "ports": [80, 443], "debug": false}' | mq -I json -F xml '.'

Input (`books.xml`)

<?xml version="1.0" encoding="UTF-8"?>
<library>
  <book id="b1" lang="en">
    <title>Dune</title>
    <year>1965</year>
  </book>
  <book id="b2" lang="ja">
    <title>Kokoro</title>
    <year>1914</year>
  </book>
</library>

Output

XML to a plain JSON array:

[
  {
    "id": "b1",
    "title": "Dune",
    "year": 1965
  },
  {
    "id": "b2",
    "title": "Kokoro",
    "year": 1914
  }
]

JSON to XML:

<?xml version="1.0" encoding="UTF-8"?>
<root>
  <name>web</name>
  <ports>
    <item>80</item>
    <item>443</item>
  </ports>
  <debug>false</debug>
</root>

See the raw tree

mq -I xml -F json '.' prints the tree that every xml function works on. For <book id="b1"><title>Dune</title><year>1965</year></book> it is:

{
  "tag": "book",
  "attributes": {
    "id": "b1"
  },
  "children": [
    {
      "tag": "title",
      "attributes": {},
      "children": [],
      "text": "Dune"
    },
    {
      "tag": "year",
      "attributes": {},
      "children": [],
      "text": "1965"
    }
  ],
  "text": null
}

Every element has the same four keys. text is null for an element that only holds other elements.

Notes

Text values are always strings, which is why the query wraps year in to_number.
JSON to XML wraps the data in a <root> element, names array entries <item>, and writes every object key as a child element. To produce attributes, build a tree in the {tag, attributes, children, text} shape and pass it to xml::xml_stringify: mq -I null 'import "xml" | xml::xml_stringify({"tag": "greeting", "attributes": {"lang": "en"}, "children": [], "text": "hello"})' prints <greeting lang="en">hello</greeting> under an XML declaration.
mq -I xml -F xml '.' file.xml reads a file and writes it back pretty-printed, which is a quick way to reformat XML. xml_stringify on a parsed tree writes it on a single line instead.
Other formats work the same way, for example mq -I yaml -F xml '.' config.yaml.
For the JSON and YAML pair, see Convert between YAML and JSON. To pull values out of XML without converting it, see Read values from an XML file.

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