Capturing Template Output in Go

Within a Go template, capturing the output of a sub-template or assigning it to a variable directly is not supported by default. This can be achieved, however, by registering a custom function and using a bytes buffer to receive the template's result.

Custom Function Registration

To capture template output, register a function with Template.Funcs() that takes the template name as an argument and returns the template's output as a string:

func execTempl(name string) (string, error) {
    buf := &bytes.Buffer{}
    err := t.ExecuteTemplate(buf, name, nil)
    return buf.String(), err
}

Template Execution and Result Capture

Execute the sub-template named 'my-template' using Template.ExecuteTemplate() and assign it to a variable:

{{$var := execTempl "my-template"}}

Output Retrieval

Retrieve the captured output and use it as needed:

See result:
{{$var}}

Complete Example

var t *template.Template

func main() {
    t = template.Must(template.New("").Funcs(template.FuncMap{
        "execTempl": execTempl,
    }).Parse(tmpl))

    if err := t.Execute(os.Stdout, nil); err != nil {
        panic(err)
    }
}

const tmpl = `
{{define "my-template"}}my-template content{{end}}

See result:
{{$var := execTempl "my-template"}}
{{$var}}
`

Output:

See result:

my-template content