Working with YAML in Go
12.06.2021
Intro
YAML is another domain specific language (DSL) that allows you to defined data. It is an alternative to JSON and is used heavily in apps such as Kubernetes. In this article, we will learn how to use YAML in Go.
Getting Started
To begin, we need to create main.go and create a Go module.
go mod init yamlexampleNow, we will first need to install a yaml package.
go get gopkg.in/yaml.v3Let's then create an example file called example.yaml and add the following.
first_name: Jan
last_name: AudreyThe basic flow is to read the file, the use the Unmarshal function to map our data to a Go map. This is very similar to other languages like JSON if you are familiar.
Now add some imports to our file.
import (
"fmt"
"io/ioutil"
"log"
"gopkg.in/yaml.v3"
)First, let's read the file
file, err := ioutil.ReadFile("example.yaml")
if err != nil {
log.Fatal(err)
}Then, let's create a generic map using interface to match anything.
data := make(map[interface{}]interface{})
err2 := yaml.Unmarshal(file, &data)
if err2 != nil {
log.Fatal(err2)
}We can then print our data.
for key, value := range data {
fmt.Println(key, value)
}Objects YAML reading
Above we mapped data to interfaces. We can map yaml to more specific interfaces as well. Let's start with a new yaml file with a list of employees.
employee1:
name: Jan
salary: 90000
employee2:
name: Mary
occupation: 60000Now, let's create a struct to hold our employee data. Copy the following to employees.yaml.
type Employee struct {
Name string
Salary int
}Next let's read the file.
file, err := ioutil.ReadFile("employees.yaml")
if err != nil {
log.Fatal(err)
}Then, we can map our data using our structure.
data := make(map[string]Employee)
err2 := yaml.Unmarshal(file, &data)
if err2 != nil {
log.Fatal(err2)
}Writing to Files
Let's end our yaml tutorial by learning to write data. We can do this using the Marshal function which does the opposite of above.
users := map[string]Employee{
"employee1": {"Jan", 90000},
"employee2": {"Mary", 60000},
}
data, err := yaml.Marshal(&users)
if err != nil {
log.Fatal(err)
}
err2 := ioutil.WriteFile("users.yaml", data, 0)
if err2 != nil {
log.Fatal(err2)
}The Full Example
Here is the full example code. You can run this by copying the contents into a file called main.go and then running go run main.go.
package main
import (
"fmt"
"io/ioutil"
"log"
"gopkg.in/yaml.v3"
)
func example1() {
file, err := ioutil.ReadFile("example.yaml")
if err != nil {
log.Fatal(err)
}
data := make(map[interface{}]interface{})
err2 := yaml.Unmarshal(file, &data)
if err2 != nil {
log.Fatal(err2)
}
for key, value := range data {
fmt.Println(key, value)
}
}
type Employee struct {
Name string
Salary int
}
func example2() {
file, err := ioutil.ReadFile("employees.yaml")
if err != nil {
log.Fatal(err)
}
data := make(map[string]Employee)
err2 := yaml.Unmarshal(file, &data)
if err2 != nil {
log.Fatal(err2)
}
}
func example3() {
users := map[string]Employee{
"employee1": {"Jan", 90000},
"employee2": {"Mary", 60000},
}
data, err := yaml.Marshal(&users)
if err != nil {
log.Fatal(err)
}
err2 := ioutil.WriteFile("users.yaml", data, 0)
if err2 != nil {
log.Fatal(err2)
}
}
func main() {
example1()
example2()
example3()
}