This is an implementation of jq command written in Go language. You can also embed gojq as a library to your Go products.

 $ echo '{"foo": 128}' | gojq '.foo'
128
 $ echo '{"a": {"b": 42}}' | gojq '.a.b'
42
 $ echo '{"id": "sample", "10": {"b": 42}}' | gojq '{(.id): .["10"].b}'
{
  "sample": 42
}
 $ echo '[{"id":1},{"id":2},{"id":3}]' | gojq '.[] | .id'
1
2
3
 $ echo '{"a":1,"b":2}' | gojq '.a += 1 | .b *= 2'
{
  "a": 2,
  "b": 4
}
 $ echo '{"a":1} [2] 3' | gojq '. as {$a} ?// [$a] ?// $a | $a'
1
2
3
 $ echo '{"foo": 4722366482869645213696}' | gojq .foo
4722366482869645213696  # keeps the precision of number while jq does not
 $ gojq -n 'def fact($n): if $n < 1 then 1 else $n * fact($n - 1) end; fact(50)'
30414093201713378043612608166064768844377641568960512000000000000 # arbitrary-precision integer calculation

Nice error messages.

 $ echo '[1,2,3]' | gojq  '.foo & .bar'
gojq: invalid query: .foo & .bar
    .foo & .bar
         ^  unexpected token "&"
 $ echo '{"foo": { bar: [] } }' | gojq '.'
gojq: invalid json: <stdin>
    {"foo": { bar: [] } }
              ^  invalid character 'b' looking for beginning of object key string

brew install itchyny/tap/gojq

go get github.com/itchyny/gojq/cmd/gojq

docker run -i --rm itchyny/gojq

• gojq is purely implemented with Go language and is completely portable. jq depends on the C standard library so the availability of math functions depends on the library. jq also depends on the regular expression library and it makes build scripts complex.
• gojq implements nice error messages for invalid query and JSON input. The error message of jq is sometimes difficult to tell where to fix the query.
• gojq does not keep the order of object keys. I understand this might cause problems for some scripts but basically we should not rely on the order of object keys. I would implement when ordered map is implemented in the standard library of Go but I'm less motivated.
• gojq supports arbitrary-precision integer calculation while jq does not. This is important to keeping the precision of numeric IDs or nanosecond values. You can use gojq to solve some mathematical problems which require big integers.
• gojq supports reading from YAML input while jq does not. gojq also supports YAML output.

You can use the gojq parser and interpreter from your Go products.

package main

import (
	"fmt"
	"log"

	"github.com/itchyny/gojq"
)

func main() {
	query, err := gojq.Parse(".foo | ..")
	if err != nil {
		log.Fatalln(err)
	}
	input := map[string]interface{}{"foo": []interface{}{1, 2, 3}}
	iter := query.Run(input) // or query.RunWithContext
	for {
		v, ok := iter.Next()
		if !ok {
			break
		}
		if err, ok := v.(error); ok {
			log.Fatalln(err)
		}
		fmt.Printf("%#v\n", v)
	}
}

• Firstly, use gojq.Parse(string) (*Query, error) to get the query from a string.
• Secondly, get the result iterator
  • using query.Run or query.RunWithContext
  • or alternatively, compile the query using gojq.Compile and then code.Run or code.RunWithContext. You can reuse the *Code against multiple inputs to avoid compiling the same query.
  • In either case, the query input should have type []interface{} for an array and map[string]interface{} for a map (just like decoded to an interface{} using the encoding/json package). You can't use []int or map[string]string, for example.
• Thirdly, iterate through the results using iter.Next() (interface{}, bool). The iterater can emit an error so make sure to handle it. Termination is notified by the second returned value of Next(). The reason why the return type is not (interface{}, error) is that the iterator can emit multiple errors and you can continue after an error.

gojq.Compile allows to configure the following compiler options.

• gojq.WithModuleLoader allows to load modules. By default, the module feature is disabled. If you want to load modules from the filesystem, use gojq.NewModuleLoader.
• gojq.WithEnvironLoader allows to configure the environment variables referenced by env and $ENV. By default, OS environment variables are not accessible due to security reason. You can use gojq.WithEnvironLoader(os.Environ) if you want.
• gojq.WithVariables allows to configure the variables which can be used in the query. Pass the values of the variables to code.Run in the same order.
• gojq.WithFunction allows to add a custom internal function.
• gojq.WithInputIter allows to use input and inputs functions. By default, these functions are disabled.

Report bug at Issues・itchyny/gojq - GitHub.

itchyny (https://github.com/itchyny)

This software is released under the MIT License, see LICENSE.