bashdd mockup

#!/bin/bash
LC_ALL=C

c=""
off=0
IFS=''

while read -r -N 1 c ; do
  if [ ${#c} -lt 1 ]; then
  # would only print when in the right range
    printf "\0"
  else
  # would only print when in the right range
    printf "%c" "$c"
  fi
  off=$(( $off + 1 ))
done < $1