Add solution for Module 4 task 2

tasks/module_4/task_2/data/2023-06-16-12-12-55-users.db.backup

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+Marat, Admin
+Ivan, User

tasks/module_4/task_2/data/2023-06-16-12-19-31-users.db.backup

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+Marat, Admin
+Ivan, User
+Peter, User

tasks/module_4/task_2/data/users.db

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+Marat, Admin
+Ivan, User
+Peter, User

tasks/module_4/task_2/scripts/db.sh

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+#!/usr/bin/env bash
+
+typeset fileName=users.db
+typeset fileDir=../data
+typeset filePath=$fileDir/$fileName
+
+# check/create db file
+if [[ "$1" != "help" && "$1" != "" && ! -f $filePath ]]; then
+    read -p "users.db does not exist. Do you want to create it? [Y/n] " answer
+    answer=${answer,,}
+    if [[ "$answer" =~ ^(yes|y)$ ]]; then
+        touch $fileName
+        echo "File ${fileName} is created."
+    else
+        echo "File ${fileName} must be created to continue. Try again." >&2
+        exit 1
+    fi
+fi
+
+function validateLatinLetters {
+    if [[ $1 =~ ^[A-Za-z_]+$ ]]; then return 0; else return 1; fi
+}
+
+function add {
+    read -p "Enter user name: " username
+    validateLatinLetters "$username"
+    if [[ "$?" == 1 ]]; then
+        echo "Name must have only latin letters. Try again."
+        exit 1
+    fi
+
+    read -p "Enter user role: " role
+    validateLatinLetters "$role"
+    if [[ "$?" == 1 ]]; then
+        echo "Role must have only latin letters. Try again."
+        exit 1
+    fi
+
+    echo "${username}, ${role}" | tee -a $filePath
+}
+
+function backup {
+    backupFileName=$(date +'%Y-%m-%d-%H-%M-%S')-${fileName}.backup
+    cp $filePath $fileDir/"$backupFileName"
+
+    echo "Backup is created."
+}
+
+function restore {
+    latestBackupFile=$(find $fileDir -name "*-${fileName}.backup" | sort | tail -n 1)
+
+    echo "${latestBackupFile}"
+
+    if [ ! -f "$latestBackupFile" ]; then
+        echo "No backup file found."
+        exit 1
+    fi
+
+    cat "$latestBackupFile" >$filePath
+
+    echo "Backup is restored."
+}
+
+function findUser {
+    read -p "Enter username to search: " username
+
+    awk -F, -v x="$username" '$1 ~ x' ../data/users.db
+
+    # don't work =(
+    if [[ "$?" == 1 ]]; then
+        echo "User not found."
+        exit 1
+    fi
+}
+
+inverseParam="$2"
+function list {
+    if [[ $inverseParam == "inverse" ]]; then
+        cat --number $filePath | tac
+    else
+        cat --number $filePath
+    fi
+}
+
+function help {
+    echo "Manages users in db. It accepts a single parameter with a command name."
+    echo
+    echo "Syntax: db.sh [command]"
+    echo
+    echo "List of available commands:"
+    echo
+    echo "add       Adds a new line to the users.db. Script must prompt user to type a
+                    username of new entity. After entering username, user must be prompted to
+                    type a role."
+    echo "backup    Creates a new file, named" $filePath".backup which is a copy of
+                    current" $fileName
+    echo "find      Prompts user to type a username, then prints username and role if such
+                    exists in users.db. If there is no user with selected username, script must print:
+                    \"User not found\". If there is more than one user with such username, print all
+                    found entries."
+    echo "list      Prints contents of users.db in format: N. username, role
+                    where N - a line number of an actual record
+                    Accepts an additional optional parameter inverse which allows to get
+                    result in an opposite order - from bottom to top"
+}
+
+case $1 in
+add) add ;;
+backup) backup ;;
+restore) restore ;;
+find) findUser ;;
+list) list ;;
+help | '' | *) help ;;
+esac