shopt -sq nocasematch
intern=( A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 . , ? )
input=($(echo "apple" | sed -e 's/[[:alnum:].,\?]/& /g' ))

count="0"

for element1 in ${input[@]}; do
    for element2 in ${intern[@]}; do
        if [[ ${element1} == ${element2} ]]; then
            echo "index: ${count} element: ${intern[${count}]} input: ${input[${count}]}"
            break
        fi
    done
    (( count++ ))
done

#!/bin/bash

INPUT="Apple"
OUTPUT=()
CIPHER=""

OUTSET="@%/zyxwvutsrqponmlkjihgfedcba"

echo "Input: ${INPUT}"

while [ ${#INPUT} -gt 0 ]; do
    case "${INPUT:0:1}" in
    A|a) OUTPUT=("${OUTPUT[@]}"  0) ;;
    B|b) OUTPUT=("${OUTPUT[@]}"  1) ;;
    C|c) OUTPUT=("${OUTPUT[@]}"  2) ;;
    D|d) OUTPUT=("${OUTPUT[@]}"  3) ;;
    E|e) OUTPUT=("${OUTPUT[@]}"  4) ;;
    F|f) OUTPUT=("${OUTPUT[@]}"  5) ;;
    G|g) OUTPUT=("${OUTPUT[@]}"  6) ;;
    H|h) OUTPUT=("${OUTPUT[@]}"  7) ;;
    I|i) OUTPUT=("${OUTPUT[@]}"  8) ;;
    J|j) OUTPUT=("${OUTPUT[@]}"  9) ;;
    K|k) OUTPUT=("${OUTPUT[@]}" 10) ;;
    L|l) OUTPUT=("${OUTPUT[@]}" 11) ;;
    M|m) OUTPUT=("${OUTPUT[@]}" 12) ;;
    N|n) OUTPUT=("${OUTPUT[@]}" 13) ;;
    O|o) OUTPUT=("${OUTPUT[@]}" 14) ;;
    P|p) OUTPUT=("${OUTPUT[@]}" 15) ;;
    Q|q) OUTPUT=("${OUTPUT[@]}" 16) ;;
    R|r) OUTPUT=("${OUTPUT[@]}" 17) ;;
    S|s) OUTPUT=("${OUTPUT[@]}" 18) ;;
    T|t) OUTPUT=("${OUTPUT[@]}" 19) ;;
    U|u) OUTPUT=("${OUTPUT[@]}" 20) ;;
    V|v) OUTPUT=("${OUTPUT[@]}" 21) ;;
    W|w) OUTPUT=("${OUTPUT[@]}" 22) ;;
    X|x) OUTPUT=("${OUTPUT[@]}" 23) ;;
    Y|y) OUTPUT=("${OUTPUT[@]}" 24) ;;
    Z|z) OUTPUT=("${OUTPUT[@]}" 25) ;;
    0)   OUTPUT=("${OUTPUT[@]}" 26) ;;
    1)   OUTPUT=("${OUTPUT[@]}" 27) ;;
    2)   OUTPUT=("${OUTPUT[@]}" 28) ;;
    3)   OUTPUT=("${OUTPUT[@]}" 29) ;;
    4)   OUTPUT=("${OUTPUT[@]}" 30) ;;
    5)   OUTPUT=("${OUTPUT[@]}" 31) ;;
    6)   OUTPUT=("${OUTPUT[@]}" 32) ;;
    7)   OUTPUT=("${OUTPUT[@]}" 33) ;;
    8)   OUTPUT=("${OUTPUT[@]}" 34) ;;
    9)   OUTPUT=("${OUTPUT[@]}" 35) ;;
    '.') OUTPUT=("${OUTPUT[@]}" 36) ;;
    ',') OUTPUT=("${OUTPUT[@]}" 37) ;;
    '?') OUTPUT=("${OUTPUT[@]}" 38) ;;
    esac
    INPUT="${INPUT:1}"
done

echo "Numeric: ${OUTPUT[@]}"

for C in "${OUTPUT[@]}" ; do
    CIPHER="${CIPHER}${OUTSET:C:1}"
done

echo "Cipher: ${CIPHER}"

me@localhost:~$echo "apple" | thescript

#!/bin/bash
intern="ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.,?"

match_idxs() {
    # only do something if we have a non-empty argument
    [[ "$1" ]] && {
        # use parameter substitution (substring expansion) to cut the first character and all the rest of our argument
        # save the resulting strings in $first and $rest
        local first=${1:0:1} rest=${1:1}

        # use parameter substitution (remove matching suffix pattern) to get a copy of $intern truncated from the
        # point where it matches "$first followed by anything"
        local match="${intern%%$first*}"

        # use parameter substitution (parameter length) to echo the length of $match (its length will equal the index of $first in $intern).
        # Add the rest of the indexes to the echo, using command substitution to call ourselves over $rest.
        # $FUNCNAME is set by bash to whatever the current function is named (could have used match_idxs with the same result, but this way is more flexible).
        echo "${#match} $($FUNCNAME $rest)"
    }
}

# Loop over our standard input, line by line until EOF. On each iteration, $line will hold current line.
# On each iteration, print indexes for every character of this line.
# We call the match_idxs function passing to it the line converted to all caps (parameter expansion - case modification)
while read line; do
    match_idxs "${line^^}"
done

#!/bin/bash

intern="ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.,?"
line=${1^^}

for (( i = 0; i < ${#line}; i++ ))
do
    match=${intern%%${line:i:1}*}
    echo -n "${#match} "
done

echo

#!/bin/bash

# populate the associative array, with each element holding the next sequential integer

declare -A index
n=0

for i in {A..Z} {0..9} {.,\,,?}; do
     index[$i]=$(( n++ ))	#must use "$i" here, as it outputs a string.
done

# break the input string into individual characters, and add to a regular array

for (( i = 0; i < ${#1}; i++ )) ; do
     input[i]=${1:$i:1}
done

# For each element in the input array, add its corresponding associative array value to the output array.
# ${var^^} forces the values to uppercase first.

for i in "${input[@]^^}"; do
     output+=( "${index[$i]}" )
done

# print the output array.  ${arr[*]} allows the use of IFS to define the delimiting character.
# e.g. set IFS=$'\n' first to output one entry per line.

echo "${output[*]}"

exit 0

for i in "${input[@]^^}"; do
     output+=( "${index[$i]:-*}" )
done