spread-regex

#!/bin/sh

if [ "$#" -lt "2" ]; then
  echo 'You need to provide two parameters: the amount of chars to allow ' \
    'between each searched char, and the string to sperad out. The amount ' \
    'may be negative, in which case the search string is reversed and the ' \
    'rest of the search continues as usual.' >&2
  exit 1
  fi

# $1 - how many chars to allow between each searched char
amount="$1"
shift

if ! { echo "$amount" | grep '^[0-9-][0-9]*$' >/dev/null 2>&1; }; then
  echo 'The amount must be a number' >&2
  exit 1
  fi

# $2 - search string to spread out
search="$1"

if [ "$amount" -lt 0 ]; then
  amount=$((0-amount))
  search="$(echo "$search" | awk '
    {
      for (i=length; i!=0; i--) {
        rev=rev substr($0,i,1)  # append one char to string rev
        }
      }
    END {
      print rev
      }')"
  fi

echo "$search" \
  | sed -e 's/./&.\\{0,'"$amount"'\\}/g' \
  | sed -e 's/\.\\{0,'"$amount"'\\}$//g'