jsonpath is used to pull values out of a JSON document without unmarshalling the string into an object. At the loss of post-parse random access and conversion to primitive types, you gain faster return speeds and lower memory utilization. If the value you want is located near the start of the json, the evaluator will terminate after reaching and recording its destination.

The evaluator can be initialized with several paths, so you can retrieve multiple sections of the document with just one scan. Naturally, when all paths have been reached, the evaluator will early terminate.

For each value returned by a path, you'll also get the keys & indexes needed to reach that value. Use the keys flag to view this in the CLI. The Go package will return an []interface{} of length n with indexes 0 - (n-2) being the keys and the value at index n-1.

go get github.com/NodePrime/jsonpath/cli/jsonpath
cat yourData.json | jsonpath -k -p '$.Items[*].title+'

-f, --file="": Path to json file  
-j, --json="": JSON text  
-k, --keys=false: Print keys & indexes that lead to value  
-p, --path=[]: One or more paths to target in JSON

go get github.com/NodePrime/jsonpath

paths, err := jsonpath.ParsePaths(pathStrings ...string) {

eval, err := jsonpath.EvalPathsInBytes(json []byte, paths) 
// OR
eval, err := jsonpath.EvalPathsInReader(r io.Reader, paths)

then

for {
	if result, ok := eval.Next(); ok {
		fmt.Println(result.Pretty(true)) // true -> show keys in pretty string
	} else {
		break
	}
}
if eval.Error != nil {
	return eval.Error
}

eval.Next() will traverse JSON until another value is found. This has the potential of traversing the entire JSON document in an attempt to find one. If you prefer to have more control over traversing, use the eval.Iterate() method. It will return after every scanned JSON token and return ([]*Result, bool). This array will usually be empty, but occasionally contain results.

All paths start from the root node $. Similar to getting properties in a JavaScript object, a period .title or brackets ["title"] are used.

Expressions

• paths (that start from current node @)
• numbers (integers, floats, scientific notation)
• mathematical operators (+ - / * ^)
• numerical comparisos (< <= > >=)
• logic operators (&& || == !=)
• parentheses (2 < (3 * 5))
• static values like (true, false)
• @.value > 0.5

Example: this will only return tags of all items that match this expression. $.Items[*]?(@.title == "A Tale of Two Cities").tags

Example:

{  
	"Items":   
		[  
			{  
				"title": "A Midsummer Night's Dream",  
				"tags":[  
					"comedy",  
					"shakespeare",  
					"play"  
				]  
			},{  
				"title": "A Tale of Two Cities",  
				"tags":[  
					"french",  
					"revolution",  
					"london"  
				]  
			}  
		]  
} 

Example Paths:
CLI

jsonpath --file=example.json --path='$.Items[*].tags[*]+' --keys

"Items" 0 "tags" 0 "comedy"
"Items" 0 "tags" 1 "shakespeare"
"Items" 0 "tags" 2 "play"
"Items" 1 "tags" 0 "french"
"Items" 1 "tags" 1 "revolution"
"Items" 1 "tags" 2 "london"

Paths
$.Items[*].title+
... "A Midsummer Night's Dream"
... "A Tale of Two Cities"

$.Items[*].tags+
... ["comedy","shakespeare","play"]
... ["french","revolution","london"]

$.Items[*].tags[*]+
... "comedy"
... "shakespeare"
... "play"
... "french"
... "revolution"
... "london"

... = keys/indexes of path