Reusable script for prompting user imput, supported with cache

prompt_user_input.sh

#!/bin/sh

TMP_DIR=".tmp"
mkdir -p $TMP_DIR
PROMPT_DIR="prompt"
mkdir -p $TMP_DIR/$PROMPT_DIR

# INPUT VARIABLES
#   $1 - Global variable name to write prompt into
#   $2 - Input prompt message for user
#   $3 - Reuse cache prompt message for user
#   $4 - Reuse cache message reminder for user
#   $5 - Valid input message for user
#   $6 - Invalid input message for user
#
#   Example usage:
#
#       promptUserEntry \
#           'gcpProjectID' \
#           'Please input your Google Cloud Platform Project ID:' \
#           'Use the same project id? (Y/n):' \
#           'You previously inputted GCP Project ID as' \
#           'You inputted GCP Project ID as' \
#           'Please input a valid value.'
#     
#
# OUTPUT VARIABLES
#   None
#
promptUserEntry(){
    local _outputVar=$1
    local _inputPrompt=$2
    local _reuseCacheValuePrompt=$3
    local _reuseCacheValueMessage=$4
    local _validInputMessage=$5
    local _invalidInputMessage=$6

    local _promptCacheFilename="$TMP_DIR/$PROMPT_DIR/$_outputVar"
    local _reuseCacheDecision=""
    local _userPrompt=""

    if [ -e $_promptCacheFilename ]; then
        _userPrompt=`cat $_promptCacheFilename`
        echo "$_reuseCacheValueMessage \"$_userPrompt\""
        
        while true; do
            read -p "$(echo $_reuseCacheValuePrompt) " _reuseCacheDecision
            case $_reuseCacheDecision in
                Y|y ) echo ""; eval $_outputVar="'$_userPrompt'"; return 0;;
                N|n ) break;;
                * ) echo $_invalidInputMessage;;
            esac
        done
    fi

    while true; do
        read -p "$(echo $_inputPrompt) " _userPrompt
        case $_userPrompt in
            "") echo $_invalidInputMessage;;
            * ) echo $_userPrompt > $_promptCacheFilename; break;;
        esac
    done
    echo "$_validInputMessage \"$_userPrompt\"\n"

    eval $_outputVar="'$_userPrompt'"
}