How to Capture Go Template Output and Assign it to a Variable?
Dec 23, 2024 am 01:22 AM
Capture or Assign Go Template Output to Variable
Within a Go template, the goal is to emulate the following:
{{$var := template "my-template"}}
However, this approach results in the error "unexpected in operand."
Solution
Go does not provide an inbuilt method to capture template execution results. Instead, register a function that performs this task.
Function Registration
Use the Template.Funcs() function to register functions. Execute named templates with Template.ExecuteTemplate() and use a bytes.Buffer as the target to capture the direct template execution result into a buffer.
Example
package main
import (
"bytes"
"html/template"
"log"
"os"
)
var t *template.Template
func execTempl(name string) (string, error) {
buf := &bytes.Buffer{}
err := t.ExecuteTemplate(buf, name, nil)
return buf.String(), err
}
func main() {
t = template.Must(template.New("").Funcs(template.FuncMap{
"execTempl": execTempl,
}).Parse(tmpl))
if err := t.Execute(os.Stdout, nil); err != nil {
log.Fatal(err)
}
}
const tmpl = `{{define "my-template"}}my-template content{{end}}
See result:
{{$var := execTempl "my-template"}}
{{$var}}
`
Usage
Execute the "my-template" template using the registered execTempl() function. Store the result in the $var template variable, which can then be added to the output or passed to other functions.
Output
See result: my-template content
Note that the output captures the result of the "my-template" template and displays it within the main template.
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