How to Capture Go Template Output into a Variable?

Capturing Template Output in Go

Within a Go template, it's impossible to directly assign a template output to a variable using the syntax {$var := template}. Instead, it's necessary to register a custom function to capture the template output.

Function Registration

To register a function, use the Template.Funcs() function. It allows you to define a set of functions that can be used within your template.

Template Execution

To execute a named template and capture its output, use Template.ExecuteTemplate(). This function takes a buffer as its target, allowing you to directly write the template output into the buffer.

Example

Here's an example that demonstrates the use of a registered function to capture template output:

package main

import (
    "bytes"
    "fmt"
    "text/template"
)

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 {
        panic(err)
    }
}

const tmpl = `{{define "my-template"}}my-template content{{end}}
See result:
{{$var := execTempl "my-template"}}
{{$var}}
`

Output:

See result:

my-template content

In this example, the execTempl() function is registered and used within the template to execute the "my-template" template and capture its output, which is then assigned to the $var template variable and displayed in the output.

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