Two ways:

1. Interpolate:

   You need to wrap the variable name in curlies to prevent the 's' being taken as a part of it:

   $space = 5; 
   printf "%${space}s\n", 'x';;
      x
   [download]

2. Let printf fill in the value for you by using the '*' specifier:

   $space = 5; 
   printf "%*s\n", $space, 'x';;
      x
   [download]