JSONPath
External
- https://goessner.net/articles/JsonPath/
- https://github.com/json-path/JsonPath
- https://support.smartbear.com/alertsite/docs/monitors/api/endpoint/jsonpath.html
- https://github.com/jayway/JsonPath
Internal
Overview
JSONPath is a query language for JSON similar to XPath for XML. Some documentation describes it as a Java DSL for reading JSON documents, probably to address those cases where the implementation is made in Java.
JSONPath Expression
A JSONPath expression specifies a path to an element or a set of elements that are part of a JSON document.
.spec.containers[0].name
An expression can be assembled using a series of syntax elements presented below.
$
$ represents the top-level element (or root) of the JSON document. The "$" is optional, the following are equivalent:
$.metadata
.metadata
Some JSONPath documentation mentions that even the leading dot can be omitted, but that may break some tools, as it is the case with kubectl JSONPath support.
Element Selection
There are two ways to select a specific child element relative to the parent element: the dot notation .field (or its variant ['field ']) and index-based selection. These two different forms are applied to JSON Objects and Arrays, respectively, given the fact that JSON has only these two types of collections.
Object Fields Selection
.field
This is called "the dot notation". The expression selects the specified field in the parent JSON Object.
.metadata.resourceVersion
['field']
This is an equivalent variant of the dot notation that can used to select the specified field of a parent Object. It requires quotes around the field name and it is useful when the field name contains special characters such as spaces, or they begin with a character other than A..Za..z_.
['metadata']['resourceVersion']
Note that some tools, such as kubectl JSONPath support, do not support this notation.
Array Element Selection
Array elements are selected using 0-based indexes.
[0-based-index]
The expression selects the element whose index is specified between square brackets from a JSON Array.
[index1, index2, ...]
The expression selects the elements with the specified indexes from a JSON Array and returns a space-separated list. If the element with the specified index does not exist, the result is tool-dependent. For example, kubectl JSONPath support raises an error.
[start:end], [start:]
The expression selects the elements from the start index and up to, but not including, the end index. If end is omitted, it selects all elements from start until the end of the array. It returns a space-separated list.