Wordle in 20 lines of bash

wordle.bash

#!/usr/bin/env bash
mapfile -t words < <(grep -x '[a-z]\{5\}' "${WORDLIST:-/usr/share/dict/words}")
word=${words[RANDOM % ${#words[@]}]} pool=abcdefghijklmnopqrstuvwxyz
for ((round=1; round <= ${ROUNDS:=6}; round++)); do
	while read -rp "$round/$ROUNDS: " guess || exit 1; do
		[[ " ${words[@]} " == *" ${guess,,} "* ]] && guess=${guess,,} && break
	done
	for ((i=0, chars=0; i < ${#word}; i++)); do
		[[ ${word:i:1} != ${guess:i:1} ]] && chars+=${word:i:1}
	done
	for ((i=0; color=7, i < ${#guess}; i++)); do char=${guess:i:1}
		{ [[ ${word:i:1} == $char ]] && color=2; } ||
		{ [[ ${chars#0} == *$char* ]] && color=3 chars=${chars/$char/}; }
		[[ $word != *$char* ]] && pool=${pool/$char/}
		printf '\033[30;4%dm %s \033[0m' "$color" "${char^^}"
	done
	printf ' %s\n' "$pool"
	[[ $guess == $word ]] && exit
done
! printf 'The word was "%s"\n' "$word" && false

@jcromero chars has to be set anew every round, so letting it uninitialized only works for the first time. It's set to 0 because it's not possible to set something to a string inside an arithmetic expression.

@matthewpersico nice but because the goal was to do it in as few lines as possible, I'd reduce the help logic to a single line. I'd also get rid of the declare and use "${letters:=${CHARS:=5}}". I thought about making the word length configurable but didn't do it because you can run abritary code using $CHARS.

[Edit] 3 extra lines.: CHARS and ROUNDS can only be integers. Help is printed to stderr when any argument is given. Amount of rounds and word length is printed once at the start.

#!/usr/bin/env bash
printf '%d%d' "${CHARS:=5}" "${ROUNDS:=6}" &>/dev/null || set 1
[[ $# != 0 ]] && { printf '[CHARS=n] [ROUNDS=n] [WORDLIST=file] %s\n' "${0##*/}" >&2; exit 1; }
printf 'Letters: %d Rounds: %d\n' "${CHARS#-}" "$ROUNDS"
mapfile -t words < <(grep -x '[a-z]\{'"${CHARS#-}"'\}' "${WORDLIST:-/usr/share/dict/words}")
word=${words[RANDOM % ${#words[@]}]} pool=abcdefghijklmnopqrstuvwxyz
for ((round=1; round <= $ROUNDS; round++)); do
	while read -rp "$round/$ROUNDS: " guess || exit 1; do
		[[ " ${words[*]} " == *" ${guess,,} "* ]] && guess=${guess,,} && break
	done
	for ((i=0, chars=0; i < ${#word}; i++)); do
		[[ ${word:i:1} != "${guess:i:1}" ]] && chars+=${word:i:1}
	done
	for ((i=0; color=7, i < ${#guess}; i++)); do char=${guess:i:1}
		{ [[ ${word:i:1} == "$char" ]] && color=2; } ||
		{ [[ ${chars#0} == *"$char"* ]] && color=3 chars=${chars/$char/}; }
		[[ $word != *"$char"* ]] && pool=${pool/$char/}
		printf '\033[30;4%dm %s \033[0m' "$color" "${char^^}"
	done
	printf ' %s\n' "$pool"
	[[ $guess == "$word" ]] && exit
done
! printf 'The word was "%s"\n' "$word" && false

@jcromero - Because I didn't quite grok what was going on and wanted to disturb as little a possible.

@aaronNGi - sweet. Thank you for considering my edits.