The jq tool is a lightweight and flexible command-line JSON processor. It allows you to extract, transform, and manipulate JSON data using a simple and expressive query language. In this guide, we'll explore how to use jq to work with JSON data in various ways. But instead of just being able to read json, this tools will also be able to read and process xml data.
To create a jq-like program in Go that can parse CSV, JSON, and XML, and read from both file and stdin, follow these steps:
Step 1: Initialize the Go Module
First, create a new directory for your project and initialize the Go module.
mkdir jq_program
cd jq_program
go mod init github.com/username/jq_program
Step 2: Install Dependencies
You will need the following libraries:
github.com/tidwall/gjson for JSON parsing
github.com/clbanning/mxj for XML parsing
github.com/jszwec/csvutil for CSV parsing
go get github.com/tidwall/gjson
go get github.com/clbanning/mxj
go get github.com/jszwec/csvutil
Step 3: Create the jq.go File
Create a lib/jq.go file to handle the JSON, XML, and CSV functionality.
// jq.go
package lib
import (
"fmt"
"io"
"os"
"github.com/clbanning/mxj"
"github.com/jszwec/csvutil"
"github.com/tidwall/gjson"
)
// ProcessJSON processes JSON input and applies a query.
func ProcessJSON(jsonData, query string) string {
result := gjson.Get(jsonData, query)
return result.String()
}
// ProcessXML processes XML input and applies a query.
func ProcessXML(xmlData, query string) string {
mv, err := mxj.NewMapXml([]byte(xmlData))
if err != nil {
return fmt.Sprintf("Error parsing XML: %v", err)
}
result, err := mv.ValueForPath(query)
if err != nil {
return fmt.Sprintf("Error querying XML: %v", err)
}
return fmt.Sprintf("%v", result)
}
// ProcessCSV processes CSV input and applies a query.
func ProcessCSV(csvData, query string) string {
var records []map[string]interface{}
if err := csvutil.Unmarshal([]byte(csvData), &records); err != nil {
return fmt.Sprintf("Error parsing CSV: %v", err)
}
for _, record := range records {
if value, ok := record[query]; ok {
return fmt.Sprintf("%v", value)
}
}
return "Query not found"
}
// ReadFile reads the content of a file.
func ReadFile(filePath string) (string, error) {
data, err := os.ReadFile(filePath)
if err != nil {
return "", err
}
return string(data), nil
}
// ReadStdin reads the content from standard input.
func ReadStdin() (string, error) {
data, err := io.ReadAll(os.Stdin)
if err != nil {
return "", err
}
return string(data), nil
}
Step 4: Create the main.go File
Create a main.go file to use the JSON, XML, and CSV functionality.
// main.go
package main
import (
"flag"
"fmt"
"os"
"github.com/username/jq/lib"
)
func main() {
file := flag.String("file", "", "Path to the file (CSV, JSON, or XML)")
query := flag.String("query", "", "Query to apply to the data")
format := flag.String("format", "json", "Format of the input data (csv, json, or xml)")
flag.Parse()
if *query == "" {
fmt.Println("Usage: jq_program --file <file_path> --query <query> --format <csv|json|xml>")
os.Exit(1)
}
var data string
var err error
if *file != "" {
data, err = lib.ReadFile(*file)
if err != nil {
fmt.Printf("Error reading file: %v\n", err)
os.Exit(1)
}
} else {
data, err = lib.ReadStdin()
if err != nil {
fmt.Printf("Error reading stdin: %v\n", err)
os.Exit(1)
}
}
var result string
switch *format {
case "json":
result = lib.ProcessJSON(data, *query)
case "xml":
result = lib.ProcessXML(data, *query)
case "csv":
result = lib.ProcessCSV(data, *query)
default:
fmt.Println("Unsupported format. Use 'csv', 'json', or 'xml'.")
os.Exit(1)
}
fmt.Println(result)
}
Step 5: Run the Program
Run the program using the go run command.
To read JSON from a file:
go run main.go --file example.json --query "key.nestedKey" --format json
To read XML from a file:
go run main.go --file example.xml --query "key.nestedKey" --format xml
To read CSV from a file:
go run main.go --file example.csv --query "columnName" --format csv
To read JSON from standard input:
cat example.json | go run main.go --query "key.nestedKey" --format json
To read XML from standard input:
cat example.xml | go run main.go --query "key.nestedKey" --format xml
To read CSV from standard input:
cat example.csv | go run main.go --query "columnName" --format csv
Replace example.json, example.xml, or example.csv with the path to your file and key.nestedKey or columnName with your desired query. This will parse the JSON, XML, or CSV data and extract the value based on the query.
Last modified: 08 January 2025