How to Capture Go Template Output and Assign it to a Variable?

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

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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