Find valid words (not full solutions) to the New York Times' Letter Boxed game

letter-boxed.sh

#!/usr/bin/env bash

set -euo pipefail

readonly WORDS="${WORDS-/usr/share/dict/words}"
readonly MINIMUM_LENGTH="${MINIMUM_LENGTH-3}"

limit-alphabet() {
  local alphabet="$1"
  grep -E "^[${alphabet}]{${MINIMUM_LENGTH},}$"
}

remove-invalid() {
  local side="$1"
  local -a regex=()

  local -i i
  local letter
  for (( i=0; i<${#side}; i++ )); do
    letter="${side:${i}:1}"
    regex+=("${letter}[${side}]")
  done

  grep -Ev "$(IFS=\|; echo "${regex[*]}")"
}

main() {
  local top="$1"
  local left="$2"
  local bottom="$3"
  local right="$4"

  {
    limit-alphabet "${top}${left}${bottom}${right}" \
    | remove-invalid "${top}" \
    | remove-invalid "${left}" \
    | remove-invalid "${bottom}" \
    | remove-invalid "${right}"
  } \
  < "${WORDS}"
}

main "$@"