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Josh Baker
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# GJSON Path Syntax
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A GJSON Path is a text string syntax that describes a search pattern for quickly retreiving values from a JSON payload.
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This document is designed to explain the structure of a GJSON Path through examples.
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- [Path structure](#path-structure)
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- [Basic](#basic)
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- [Wildcards](#wildcards)
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- [Escape Character](#escape-character)
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- [Arrays](#arrays)
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- [Queries](#queries)
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- [Dot vs Pipe](#dot-vs-pipe)
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- [Modifiers](#modifiers)
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The definitive implemenation is [github.com/tidwall/gjson](https://github.com/tidwall/gjson).
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## Path structure
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A GJSON Path is intended to be easily expressed as a series of components seperated by a `.` character.
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Along with `.` character, there are a few more that have special meaning, including `|`, `#`, `@`, `\`, `*`, and `?`.
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## Example
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Given this JSON
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```json
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{
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"name": {"first": "Tom", "last": "Anderson"},
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"age":37,
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"children": ["Sara","Alex","Jack"],
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"fav.movie": "Deer Hunter",
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"friends": [
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{"first": "Dale", "last": "Murphy", "age": 44},
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{"first": "Roger", "last": "Craig", "age": 68},
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{"first": "Jane", "last": "Murphy", "age": 47}
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]
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}
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```
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The following GJSON Paths evaluate to the accompanying values.
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### Basic
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In many cases you'll just want to retreive values by object name or array index.
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```go
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name.last "Anderson"
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name.first "Tom"
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age 37
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children ["Sara","Alex","Jack"]
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children.0 "Sara"
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children.1 "Alex"
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friends.1 {"first": "Roger", "last": "Craig", "age": 68}
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friends.1.first "Roger"
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```
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### Wildcards
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A key may contain the special wildcard characters `*` and `?`.
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The `*` will match on any zero+ characters, and `?` matches on any one character.
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```go
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child*.2 "Jack"
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c?ildren.0 "Sara"
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```
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### Escape character
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Special purpose characters, such as `.`, `*`, and `?` can be escaped with `\`.
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```go
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fav\.movie "Deer Hunter"
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```
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### Arrays
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The `#` character allows for digging into JSON Arrays.
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To get the length of an array you'll just use the `#` all by itself.
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```go
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friends.# 3
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friends.#.age [44,68,47]
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```
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### Queries
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You can also query an array for the first match by using `#[...]`, or find all matches with `#[...]#`.
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Queries support the `==`, `!=`, `<`, `<=`, `>`, `>=` comparison operators,
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and the simple pattern matching `%` (like) and `!%` (not like) operators.
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```go
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friends.#[last=="Murphy"].first "Dale"
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friends.#[last=="Murphy"]#.first ["Dale","Jane"]
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friends.#[age>45]#.last ["Craig","Murphy"]
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friends.#[first%"D*"].last "Murphy"
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friends.#[first!%"D*"].last "Craig"
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```
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To query for a non-object value in an array, you can forgo the string to the right of the operator.
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```go
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children.#[!%"*a*"] "Alex"
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children.#[%"*a*"]# ["Sara","Jack"]
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```
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### Dot vs Pipe
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The `.` is standard separator, but it's also possible to use a `|`.
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In most cases they both end up returning the same results.
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The cases where`|` differs from `.` is when it's used after the `#` for [Arrays](#arrays) and [Queries](#queries).
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Here are some examples
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```go
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friends.0.first "Dale"
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friends|0.first "Dale"
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friends.0|first "Dale"
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friends|0|first "Dale"
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friends|# 3
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friends.# 3
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friends.#[last="Murphy"]# [{"first": "Dale", "last": "Murphy", "age": 44},{"first": "Jane", "last": "Murphy", "age": 47}]
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friends.#[last="Murphy"]#.first ["Dale","Jane"]
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friends.#[last="Murphy"]#|first <non-existent>
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friends.#[last="Murphy"]#.0 []
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friends.#[last="Murphy"]#|0 {"first": "Dale", "last": "Murphy", "age": 44}
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friends.#[last="Murphy"]#.# []
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friends.#[last="Murphy"]#|# 2
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```
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Let's break down a few of these.
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The path `friends.#[last="Murphy"]#` all by itself results in
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```json
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[{"first": "Dale", "last": "Murphy", "age": 44},{"first": "Jane", "last": "Murphy", "age": 47}]
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```
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The `.first` suffix will process the `first` path on each array element *before* returning the results. Which becomes
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```json
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["Dale","Jane"]
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```
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But the `|first` suffix actually processes the `first` path *after* the previous result.
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Since the previous result is an array, not an object, it's not possible to process
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because `first` does not exist.
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Yet, `|0` suffix returns
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```json
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{"first": "Dale", "last": "Murphy", "age": 44}
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```
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Because `0` is the first index of the previous result.
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### Modifiers
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A modifier is a path component that performs custom processing on the JSON.
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For example, using the built-in `@reverse` modifier on the above JSON payload will reverse the `children` array:
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```go
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children.@reverse ["Jack","Alex","Sara"]
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children.@reverse.0 "Jack"
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```
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There are currently three built-in modifiers:
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- `@reverse`: Reverse an array or the members of an object.
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- `@ugly`: Remove all whitespace from JSON.
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- `@pretty`: Make the JSON more human readable.
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#### Modifier arguments
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A modifier may accept an optional argument. The argument can be a valid JSON payload or just characters.
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For example, the `@pretty` modifier takes a json object as its argument.
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```
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@pretty:{"sortKeys":true}
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```
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Which makes the json pretty and orders all of its keys.
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```json
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{
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"age":37,
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"children": ["Sara","Alex","Jack"],
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"fav.movie": "Deer Hunter",
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"friends": [
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{"age": 44, "first": "Dale", "last": "Murphy"},
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{"age": 68, "first": "Roger", "last": "Craig"},
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{"age": 47, "first": "Jane", "last": "Murphy"}
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],
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"name": {"first": "Tom", "last": "Anderson"}
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}
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```
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*The full list of `@pretty` options are `sortKeys`, `indent`, `prefix`, and `width`.
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Please see [Pretty Options](https://github.com/tidwall/pretty#customized-output) for more information.*
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#### Custom modifiers
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You can also add custom modifiers.
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For example, here we create a modifier which makes the entire JSON payload upper or lower case.
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```go
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gjson.AddModifier("case", func(json, arg string) string {
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if arg == "upper" {
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return strings.ToUpper(json)
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}
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if arg == "lower" {
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return strings.ToLower(json)
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}
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return json
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})
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"children.@case:upper" ["SARA","ALEX","JACK"]
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"children.@case:lower.@reverse" ["jack","alex","sara"]
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```
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