wordle.sh

#!/bin/bash -e
set -o pipefail; LC_COLATE=C

: "${LETTERS:=5}"
: "${ROUNDS:=7}"
: "${DICTIONARY:=/usr/share/dict/words}"

#https://www.shellhacks.com/bash-colors/
hit='\e[30;102m'; match='\e[30;103m'; miss='\e[30;107m'; reset='\e[0m'
pool=`printf '%s' {a..z}`

readlink -e "$DICTIONARY" >/dev/null

# pick first letter because uneven frequency distribution
first=${pool:(( RANDOM % ${#pool} )):1}

mapfile -t words < <( 
  ( zcat "$DICTIONARY" 2>/dev/null || cat "$DICTIONARY" ) |
      grep -xiE "^${first:?}[a-z]{$(( LETTERS - 1 ))}"
)
declare -i wc=${#words[@]}
declare -i line=$(( RANDOM % wc ))
declare -l guess='' secret=${words[$line]}
${DEBUG:+ echo $secret: $line/$wc}


function score {
  local -a pad=() matched=(); color=$reset

  # pre-mark hits with '=', then later '.' for match
  for (( i=0; i < LETTERS; i++ )); do
    c=${guess:$i:1}; k=${secret:$i:1}
    [[ "$k" == "$c" ]] && pad[$i]='=' || pad[$i]=$k
  done
  for (( i=0; i < LETTERS; i++ )); do
    c=${guess:$i:1}

    if [[ ${pad[$i]} == '=' ]]; then
      color=$hit; matched+=( "$c" )
    elif [[ "$c" == " " ]]; then
      # _hint
      color=$reset; c='_'
    elif [[ "${pad[@]}" =~ ${c:-\000} ]]; then
      # mark with '.'
      color=$match; pad=( "${pad[@]//$c/.}" ); matched+=( "$c" )
    else
      color=$miss
      [[ "${matched[@]}" =~ $c ]] || pool=${pool/$c/ }
    fi
    pool=${pool/$c/${c^^}} 
    echo -en "$color ${c^^} "
  done
  echo -e "${reset}\t\t${pool}\n"
}


#--- MAIN ---

echo "Guess the secret word ($LETTERS letters) in $ROUNDS attempts. (Type '_hint' for an assist)"
echo

for (( j=1; j <= ROUNDS; j++ )); do
  read -ep "$j/$ROUNDS: " guess

  if [[ "$guess" =~ _hint ]]; then
    offset=$(( RANDOM % LETTERS ))
    guess=`printf '%*s%*s' $((offset + 1)) "${secret:$offset:1}" $((LETTERS - offset - 1)) ' '`
  elif (( ${#guess} != LETTERS )) || ! [[ "$guess" =~ [a-z]{$LETTERS} ]]; then
    echo -e "  WARN\timproper guess"; continue
  fi
  score
  [[ "$guess" == "$secret" ]] && { echo "Congratulations!"; exit; }
done

echo "The word was '$secret'. Better luck next time!"


# dictionaries
#  [esl]='https://eslforums.com/5-letter-words/'
#  [github]='https://gist.githubusercontent.com/prichey/95db6bdef37482ba3f6eb7b4dec99101/raw/'
#  [popular]='https://raw.githubusercontent.com/dolph/dictionary/master/popular.txt'
# http://www.yougowords.com/5-letters
# http://www.newgeneralservicelist.org/
#  [system]=/usr/share/dict/words

#[ -s "$DICTIONARY" ] || {
#  command -v curl &>/dev/null || exit 1
#  #pic a dict, fetch and process
#}

just because you 'score' the user's entry as all caps is distinct and separate from overriding the keystrokes they are entering during read(). NEVER lie to the user by changing his input as he's typing it. If you want to 'score' the guess as lowercase if he used lower, and score it as upper if he used upper, then don't use declare -u or declare -l for guess.

sorry man but you're wasting time on a broken UI paradigm. The correct answer is to not do that.