Creating yaml files from template in golang - go

Question

I want to create a yaml file from a current tmpl file. Basically I want to insert values in the sample.tmpl files stored in the /templates folder and create a new yaml file in the same folder sample.yml
My sample.tmpl looks like
url : {{ .host }}
namespace: {{ .namespace }}
I'm using the following function:
func ApplyTemplate(filePath string) (err error) {
// Variables - host, namespace
type Eingest struct {
host string
namespace string
}
ei := Eingest{host: "example.com", namespace: "finance"}
var templates *template.Template
var allFiles []string
files, err := ioutil.ReadDir(filePath)
if err != nil {
fmt.Println(err)
}
for _, file := range files {
filename := file.Name()
fullPath := filePath + "/" + filename
if strings.HasSuffix(filename, ".tmpl") {
allFiles = append(allFiles, fullPath)
}
}
fmt.Println("Files in path: ", allFiles)
// parses all .tmpl files in the 'templates' folder
templates, err = template.ParseFiles(allFiles...)
if err != nil {
fmt.Println(err)
}
s1 := templates.Lookup("sample.tmpl")
s1.ExecuteTemplate(os.Stdout, "sample.yml", ei)
fmt.Println()
return
}
s1.ExecuteTemplate() writes to stdout. How can I create a new file in the same folder? I believe something similar is used to build kubernetes yaml files. How do we achieve this using golang template package?

Answer 1

First: since you've already looked up the template, you should use template.Execute instead, but the same works with ExecuteTemplate.
text.Template.Execute takes a io.Writer as first argument. This is an interface with a single method: Write(p []byte) (n int, err error).
Any type that has that method implements the interface and can be used as a valid argument. One such type is a os.File. Simply create a new os.File object and pass it to Execute as follows:
// Build the path:
outputPath := filepath.Join(filepath, "sample.yml")
// Create the file:
f, err := os.Create(outputPath)
if err != nil {
panic(err)
}
defer f.Close() // don't forget to close the file when finished.
// Write template to file:
err = s1.Execute(f, ei)
if err != nil {
panic(err)
}
Note: don't forget to check whether s1 is nil, as documented in template.Lookup.