---
layout: default
title: Output Formats
---
<div class="hgroup">
<div class="hgroup-inline">
<div class="panel">
<h1 id="top">Output Formats</h1>
</div>
<div style="clear: both"></div>
</div>
</div>
<div class="hgroup">
<div class="hgroup-inline">
<div class="panel">
<p>
A Jsonnet evaluation typically outputs a JSON document. For ways to output multiple JSON
documents, see <a href="/learning/getting_started.html">Getting Started</a>. Whether this
integrates cleanly depends on your application. If you're writing a custom application,
then you can simply consume this JSON. Another option is to write your config as a protocol
buffer and deserialize Jsonnet's JSON output using the proto3 canonical JSON representation.
Interoperation with YAML is also easy, see <a
href="/articles/kubernetes.html">Kubernetes</a> for an example. To support consumers of
syntactically incompatible formats such as INI or XML, custom serialization is needed.
</p>
</div>
<div style="clear: both"></div>
</div>
</div>
<div class="hgroup">
<div class="hgroup-inline">
<div class="panel">
<h2 id="top">Custom Output Formats</h2>
</div>
<div style="clear: both"></div>
</div>
</div>
<div class="hgroup">
<div class="hgroup-inline">
<div class="panel">
<p>
The INI format provides a simple example.
</p>
<ul>
<li>
The content of the INI file has been represented within the JSON object model, i.e. using
objects to represent the nesting of the sections.
</li>
<li>
The special <code>main</code> section holds the top-level keys (ones not in any section).
</li>
<li>
The function <code>std.manifestIni</code> (written in Jsonnet) serializes the structure to
a string.
</li>
<li>
Jsonnet is run in string output mode <tt>-S</tt> to print the string verbatim rather than
encoded as JSON.
</li>
</ul>
<p>
The code below could be executed with the command:
</p>
<pre>$ jsonnet -S ini.jsonnet</pre>
<p>
Try replacing <code>manifestIni</code>. with <code>manifestJson</code> or
<code>manifestPython</code>. There are many such functions in the standard library, and you
can write custom ones too. Finally, to see the effect of <tt>-S</tt> directly, try
replacing the whole buffer with just a string literal.
</p>
</div>
<div style="clear: both"></div>
</div>
</div>
<div class="inverse hgroup">
<div class=hgroup-inline>
<div class="tab-window-input" id="ini-input">
<div class="tab-header">
</div>
<textarea id=ini-jsonnet>
std.manifestIni({
main: {
a: 1,
},
sections: {
foo: {
a: true,
b: 2,
},
bar: {
x: 'text',
},
},
})
</textarea>
</div>
<div class="bigarrow">➡</div>
<div class="tab-window-output" id="ini-output">
<div class="tab-header">
<div class=selected onclick="tab_output_click(this, 'output-ini')">
output.ini
</div>
</div>
<textarea readonly class="selected code-json" id="output-ini">
a = 1
[bar]
x = text
[foo]
a = 1
b = 2
</textarea>
</div>
<script>
demo(
'ini-input',
{
'ini-jsonnet': 'ini.jsonnet',
},
'ini.jsonnet',
'ini-output',
false,
true
);
</script>
<div style="clear: both"></div>
</div>
</div>
<div class="hgroup">
<div class="hgroup-inline">
<div class="panel">
<p>
Thus, despite internally using the JSON data model, Jsonnet can provide config generation
for applications that consume INI.
</p>
<p>
Below is a more complex example where we construct an SVG file by emitting XML. It shows
how to write a custom manifestation function, and also a non-trivial example of representing
something in Jsonnet.
</p>
</div>
<div style="clear: both"></div>
</div>
</div>
<div class="inverse hgroup">
<div class=hgroup-inline>
<div class="tab-window-input" id="svg-input">
<div class="tab-header">
</div>
<textarea id=svg-jsonnet>
local xml = import 'xml.libsonnet';
local Svg = xml.Element('svg') {
height:: 100,
width:: 100,
};
local Polygon = xml.Element('polygon') {
points: std.join(
' ',
[
'%s,%s' % coords
for coords in self.pointCoords
]
),
};
local Path = xml.Element('path') {
cmds:: [],
d: std.join('', self.cmds),
};
local ref(element) = 'url(#%s)' % element.id;
local logo = Svg {
version: '1.1',
xmlns: 'http://www.w3.org/2000/svg',
x: 0,
y: 0,
width: 90,
height: 90,
viewBox: '0 0 180 180',
bg:: xml.Element('linearGradient') {
id: 'bg',
gradientUnits: 'userSpaceOnUse',
x1: 53,
y1: 19,
x2: 126,
y2: 162,
colour1:: '#0091AD',
colour2:: '#00728F',
local grad = self,
has: [
xml.Element('stop') {
offset: 0,
'stop-color': grad.colour1,
},
xml.Element('stop') {
offset: 1,
'stop-color': grad.colour2,
},
],
},
line:: Polygon {
fill: 'white',
pointCoords:: [
[0, 38],
[90, -14],
[180, 38],
[180, 142],
[90, 194],
[0, 142]
],
},
fill:: Path {
fill: ref($.bg),
cmds: [
'M168,49 v86 L129,82 L168,49 z',
'M90,98 l67-59 L90,0 V98 z',
'M73,10 L12,45 v90 l61,35 V10 z',
'M117,94 L90,116 v63 l63-36 L117,94 z',
],
},
has: [
$.bg,
$.line,
$.fill,
],
};
xml.manifestXmlObj(logo)
</textarea>
<textarea id=xml-libsonnet>
// Some utility functions for generating XML.
{
// Serialize a XML document represented as a
// Jsonnet value. Each node of the XML tree
// has a field 'tag', and optionally 'attrs'
// (an string mapping), and 'has', an array
// of children.
manifestXmlObj(value)::
local aux(v, cindent) =
if !std.isObject(v) then
error 'Expected a object, got %s'
% std.type(value)
else
local attrs = [
' %s="%s"' % [k, v.attrs[k]]
for k in std.objectFields(v.attrs)
];
if std.length(v.has) > 0 then
std.deepJoin([
cindent, '<', v.tag, attrs, '>\n',
[
aux(x, cindent + ' ')
for x in v.has
],
cindent, '</', v.tag, '>\n'
])
else
std.deepJoin([
cindent, '<', v.tag, attrs, '>',
'</', v.tag, '>\n']);
aux(value, ''),
// A convenience object whose attributes are
// taken from the top-level non-hidden fields
// of the object. This works except for
// attributes called 'tag' or 'has'.
Element(tag):: {
local element = self,
tag:: tag,
attrs:: {
[k]: element[k]
for k in std.objectFields(element)
},
has:: [],
},
}
</textarea>
</div>
<div class="bigarrow">➡</div>
<div class="tab-window-output" id="svg-output">
<div class="tab-header">
<div class=selected onclick="tab_output_click(this, 'output-svg')">
output.svg
</div>
</div>
<textarea readonly class="selected code-json" id="output-svg">
<svg version="1.1" viewBox="0 0 180 180" x="0" xmlns="http://www.w3.org/2000/svg" y="0">
<linearGradient gradientUnits="userSpaceOnUse" id="bg" x1="53" x2="126" y1="19" y2="162">
<stop offset="0" stop-color="#0091AD"></stop>
<stop offset="1" stop-color="#00728F"></stop>
</linearGradient>
<polygon fill="white" points="0,38 90,-14 180,38 180,142 90,194 0,142"></polygon>
<path d="M168,49 v86 L129,82 L168,49 zM90,98 l67-59 L90,0 V98 zM73,10 L12,45 v90 l61,35 V10 zM117,94 L90,116 v63 l63-36 L117,94 z" fill="url(#bg)"></path>
</svg>
</textarea>
</div>
<script>
demo(
'svg-input',
{
'svg-jsonnet': 'svg.jsonnet',
'xml-libsonnet': 'xml.libsonnet',
},
'svg.jsonnet',
'svg-output',
false,
true
);
</script>
<div style="clear: both"></div>
</div>
</div>
<div class="hgroup">
<div class="hgroup-inline">
<div class="panel">
<p>
This approach generalizes widely because JSON is very versatile. Indeed, its success as an
interchange format can be attributed to that versatility. Using the technique described
above, Jsonnet can output any format that can be represented in JSON.
</p>
</div>
<div style="clear: both"></div>
</div>
</div>