fmt.Printf

{{ $var := "world" }}
{{ printf "Hello %s." $var }} → Hello world.

{{ $pi := 3.14159265 }}
{{ printf "Pi is approximately %.2f." $pi }} → 3.14

Use the printf function with the safeHTMLAttr function:

{{ $desc := "Eat at Joe's" }}
<meta name="description" {{ printf "content=%q" $desc | safeHTMLAttr }}>

Hugo renders this to:

<meta name="description" content="Eat at Joe's">