diff --git a/wireguard-install.sh b/wireguard-install.sh
index f1ed23e..b35cd5b 100644
--- a/wireguard-install.sh
+++ b/wireguard-install.sh
@@ -4,7 +4,7 @@
 # https://github.com/angristan/wireguard-install
 
 function isRoot() {
-	if [ "$EUID" -ne 0 ]; then
+	if [ "${EUID}" -ne 0 ]; then
 		echo "You need to run this script as root"
 		exit 1
 	fi
@@ -31,11 +31,11 @@ function checkOS() {
 	if [[ -e /etc/debian_version ]]; then
 		# shellcheck disable=SC1091
 		source /etc/os-release
-		OS=$ID # debian or ubuntu
+		OS="${ID}" # debian or ubuntu
 	elif [[ -e /etc/fedora-release ]]; then
 		# shellcheck disable=SC1091
 		source /etc/os-release
-		OS=$ID
+		OS="${ID}"
 	elif [[ -e /etc/centos-release ]]; then
 		OS=centos
 	elif [[ -e /etc/arch-release ]]; then
@@ -62,35 +62,35 @@ function installQuestions() {
 
 	# Detect public IPv4 or IPv6 address and pre-fill for the user
 	SERVER_PUB_IP=$(ip -4 addr | sed -ne 's|^.* inet \([^/]*\)/.* scope global.*$|\1|p' | head -1)
-	if [[ -z $SERVER_PUB_IP ]]; then
+	if [[ -z "${SERVER_PUB_IP}" ]]; then
 		# Detect public IPv6 address
 		SERVER_PUB_IP=$(ip -6 addr | sed -ne 's|^.* inet6 \([^/]*\)/.* scope global.*$|\1|p' | head -1)
 	fi
-	read -rp "IPv4 or IPv6 public address: " -e -i "$SERVER_PUB_IP" SERVER_PUB_IP
+	read -rp "IPv4 or IPv6 public address: " -e -i "${SERVER_PUB_IP}" SERVER_PUB_IP
 
 	# Detect public interface and pre-fill for the user
 	SERVER_NIC="$(ip -4 route ls | grep default | grep -Po '(?<=dev )(\S+)' | head -1)"
-	until [[ "$SERVER_PUB_NIC" =~ ^[a-zA-Z0-9_]+$ ]]; do
-		read -rp "Public interface: " -e -i "$SERVER_NIC" SERVER_PUB_NIC
+	until [[ "${SERVER_PUB_NIC}" =~ ^[a-zA-Z0-9_]+$ ]]; do
+		read -rp "Public interface: " -e -i "${SERVER_NIC}" SERVER_PUB_NIC
 	done
 
-	until [[ "$SERVER_WG_NIC" =~ ^[a-zA-Z0-9_]+$ ]]; do
+	until [[ "${SERVER_WG_NIC}" =~ ^[a-zA-Z0-9_]+$ ]]; do
 		# shellcheck disable=SC2034
 		read -rp "WireGuard interface name: " -e -i wg0 SERVER_WG_NIC
 	done
 
-	until [[ "$SERVER_WG_IPV4" =~ ^([0-9]{1,3}\.){3}1$ ]]; do
+	until [[ "${SERVER_WG_IPV4}" =~ ^([0-9]{1,3}\.){3}1$ ]]; do
 		read -rp "Server's WireGuard IPv4 [x.x.x.1]: " -e -i 10.66.66.1 SERVER_WG_IPV4
 	done
 
-	until [[ "$SERVER_WG_IPV6" =~ ^([a-f0-9]{1,4}:){3,4}:1$ ]]; do
+	until [[ "${SERVER_WG_IPV6}" =~ ^([a-f0-9]{1,4}:){3,4}:1$ ]]; do
 		read -rp "Server's WireGuard IPv6 [x:x:x::1]: " -e -i fd42:42:42::1 SERVER_WG_IPV6
 	done
 
 	# Generate random number within private ports range
 	RANDOM_PORT=$(shuf -i49152-65535 -n1)
-	until [[ $SERVER_PORT =~ ^[0-9]+$ ]] && [ "$SERVER_PORT" -ge 1 ] && [ "$SERVER_PORT" -le 65535 ]; do
-		read -rp "Server's WireGuard port [1-65535]: " -e -i "$RANDOM_PORT" SERVER_PORT
+	until [[ "${SERVER_PORT}" =~ ^[0-9]+$ ]] && [ "${SERVER_PORT}" -ge 1 ] && [ "${SERVER_PORT}" -le 65535 ]; do
+		read -rp "Server's WireGuard port [1-65535]: " -e -i "${RANDOM_PORT}" SERVER_PORT
 	done
 
 	echo ""
@@ -104,31 +104,31 @@ function installWireGuard() {
 	installQuestions
 
 	# Install WireGuard tools and module
-	if [[ $OS == 'ubuntu' ]]; then
+	if [[ "${OS}" == 'ubuntu' ]]; then
 		apt-get install -y software-properties-common
 		add-apt-repository -y ppa:wireguard/wireguard
 		apt-get update
 		apt-get install -y "linux-headers-$(uname -r)"
 		apt-get install -y wireguard iptables resolvconf qrencode
-	elif [[ $OS == 'debian' ]]; then
+	elif [[ "${OS}" == 'debian' ]]; then
 		echo "deb http://deb.debian.org/debian/ unstable main" >/etc/apt/sources.list.d/unstable.list
 		printf 'Package: *\nPin: release a=unstable\nPin-Priority: 90\n' >/etc/apt/preferences.d/limit-unstable
 		apt update
 		apt-get install -y "linux-headers-$(uname -r)"
 		apt-get install -y wireguard iptables resolvconf qrencode
 		apt-get install -y bc # mitigate https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=956869
-	elif [[ $OS == 'fedora' ]]; then
-		if [[ $VERSION_ID -lt 32 ]]; then
+	elif [[ "${OS}" == 'fedora' ]]; then
+		if [[ "${VERSION_ID}" -lt 32 ]]; then
 			dnf install -y dnf-plugins-core
 			dnf copr enable -y jdoss/wireguard
 			dnf install -y wireguard-dkms
 		fi
 		dnf install -y wireguard-tools iptables qrencode
-	elif [[ $OS == 'centos' ]]; then
+	elif [[ "${OS}" == 'centos' ]]; then
 		curl -Lo /etc/yum.repos.d/wireguard.repo https://copr.fedorainfracloud.org/coprs/jdoss/wireguard/repo/epel-7/jdoss-wireguard-epel-7.repo
 		yum -y install epel-release
 		yum -y install wireguard-dkms wireguard-tools iptables qrencode
-	elif [[ $OS == 'arch' ]]; then
+	elif [[ "${OS}" == 'arch' ]]; then
 		pacman -S --noconfirm linux-headers
 		pacman -S --noconfirm wireguard-tools iptables qrencode
 	fi
@@ -139,33 +139,33 @@ function installWireGuard() {
 	chmod 600 -R /etc/wireguard/
 
 	SERVER_PRIV_KEY=$(wg genkey)
-	SERVER_PUB_KEY=$(echo "$SERVER_PRIV_KEY" | wg pubkey)
+	SERVER_PUB_KEY=$(echo "${SERVER_PRIV_KEY}" | wg pubkey)
 
 	# Save WireGuard settings
-	echo "SERVER_PUB_IP=$SERVER_PUB_IP
-SERVER_PUB_NIC=$SERVER_PUB_NIC
-SERVER_WG_NIC=$SERVER_WG_NIC
-SERVER_WG_IPV4=$SERVER_WG_IPV4
-SERVER_WG_IPV6=$SERVER_WG_IPV6
-SERVER_PORT=$SERVER_PORT
-SERVER_PRIV_KEY=$SERVER_PRIV_KEY
-SERVER_PUB_KEY=$SERVER_PUB_KEY" >/etc/wireguard/params
+	echo "SERVER_PUB_IP=${SERVER_PUB_IP}
+SERVER_PUB_NIC=${SERVER_PUB_NIC}
+SERVER_WG_NIC=${SERVER_WG_NIC}
+SERVER_WG_IPV4=${SERVER_WG_IPV4}
+SERVER_WG_IPV6=${SERVER_WG_IPV6}
+SERVER_PORT=${SERVER_PORT}
+SERVER_PRIV_KEY=${SERVER_PRIV_KEY}
+SERVER_PUB_KEY=${SERVER_PUB_KEY}" >/etc/wireguard/params
 
 	# Add server interface
 	echo "[Interface]
-Address = $SERVER_WG_IPV4/24,$SERVER_WG_IPV6/64
-ListenPort = $SERVER_PORT
-PrivateKey = $SERVER_PRIV_KEY" >"/etc/wireguard/$SERVER_WG_NIC.conf"
+Address = ${SERVER_WG_IPV4}/24,${SERVER_WG_IPV6}/64
+ListenPort = ${SERVER_PORT}
+PrivateKey = ${SERVER_PRIV_KEY}" >"/etc/wireguard/${SERVER_WG_NIC}.conf"
 
 	if [ -x "$(command -v firewall-cmd)" ]; then
-		FIREWALLD_IPV4_ADDRESS=$(echo "$SERVER_WG_IPV4" | cut -d"." -f1-3)".0"
+		FIREWALLD_IPV4_ADDRESS=$(echo "${SERVER_WG_IPV4}" | cut -d"." -f1-3)".0"
 		# shellcheck disable=SC2001
-		FIREWALLD_IPV6_ADDRESS=$(echo "$SERVER_WG_IPV6" | sed 's/:[^:]*$/:0/')
-		echo "PostUp = firewall-cmd --add-port $SERVER_PORT/udp && firewall-cmd --add-rich-rule='rule family=ipv4 source address=$FIREWALLD_IPV4_ADDRESS/24 masquerade' && firewall-cmd --add-rich-rule='rule family=ipv6 source address=$FIREWALLD_IPV6_ADDRESS/24 masquerade'
-PostDown = firewall-cmd --remove-port $SERVER_PORT/udp && firewall-cmd --remove-rich-rule='rule family=ipv4 source address=$FIREWALLD_IPV4_ADDRESS/24 masquerade' && firewall-cmd --remove-rich-rule='rule family=ipv6 source address=$FIREWALLD_IPV6_ADDRESS/24 masquerade'" >>"/etc/wireguard/$SERVER_WG_NIC.conf"
+		FIREWALLD_IPV6_ADDRESS=$(echo "${SERVER_WG_IPV6}" | sed 's/:[^:]*$/:0/')
+		echo "PostUp = firewall-cmd --add-port ${SERVER_PORT}/udp && firewall-cmd --add-rich-rule='rule family=ipv4 source address=${FIREWALLD_IPV4_ADDRESS}/24 masquerade' && firewall-cmd --add-rich-rule='rule family=ipv6 source address=${FIREWALLD_IPV6_ADDRESS}/24 masquerade'
+PostDown = firewall-cmd --remove-port ${SERVER_PORT}/udp && firewall-cmd --remove-rich-rule='rule family=ipv4 source address=${FIREWALLD_IPV4_ADDRESS}/24 masquerade' && firewall-cmd --remove-rich-rule='rule family=ipv6 source address=${FIREWALLD_IPV6_ADDRESS}/24 masquerade'" >>"/etc/wireguard/${SERVER_WG_NIC}.conf"
 	else
-		echo "PostUp = iptables -A FORWARD -i $SERVER_WG_NIC -j ACCEPT; iptables -t nat -A POSTROUTING -o $SERVER_PUB_NIC -j MASQUERADE; ip6tables -A FORWARD -i $SERVER_WG_NIC -j ACCEPT; ip6tables -t nat -A POSTROUTING -o $SERVER_PUB_NIC -j MASQUERADE
-PostDown = iptables -D FORWARD -i $SERVER_WG_NIC -j ACCEPT; iptables -t nat -D POSTROUTING -o $SERVER_PUB_NIC -j MASQUERADE; ip6tables -D FORWARD -i $SERVER_WG_NIC -j ACCEPT; ip6tables -t nat -D POSTROUTING -o $SERVER_PUB_NIC -j MASQUERADE" >>"/etc/wireguard/$SERVER_WG_NIC.conf"
+		echo "PostUp = iptables -A FORWARD -i ${SERVER_WG_NIC} -j ACCEPT; iptables -t nat -A POSTROUTING -o ${SERVER_PUB_NIC} -j MASQUERADE; ip6tables -A FORWARD -i ${SERVER_WG_NIC} -j ACCEPT; ip6tables -t nat -A POSTROUTING -o ${SERVER_PUB_NIC} -j MASQUERADE
+PostDown = iptables -D FORWARD -i ${SERVER_WG_NIC} -j ACCEPT; iptables -t nat -D POSTROUTING -o ${SERVER_PUB_NIC} -j MASQUERADE; ip6tables -D FORWARD -i ${SERVER_WG_NIC} -j ACCEPT; ip6tables -t nat -D POSTROUTING -o ${SERVER_PUB_NIC} -j MASQUERADE" >>"/etc/wireguard/${SERVER_WG_NIC}.conf"
 	fi
 
 	# Enable routing on the server
@@ -174,22 +174,22 @@ net.ipv6.conf.all.forwarding = 1" >/etc/sysctl.d/wg.conf
 
 	sysctl --system
 
-	systemctl start "wg-quick@$SERVER_WG_NIC"
-	systemctl enable "wg-quick@$SERVER_WG_NIC"
+	systemctl start "wg-quick@${SERVER_WG_NIC}"
+	systemctl enable "wg-quick@${SERVER_WG_NIC}"
 
 	# Check if WireGuard is running
-	systemctl is-active --quiet "wg-quick@$SERVER_WG_NIC"
+	systemctl is-active --quiet "wg-quick@${SERVER_WG_NIC}"
 	WG_RUNNING=$?
 
 	# Warn user about kernel version mismatch with headers
-	if [[ $OS =~ (fedora|centos) ]] && [[ $WG_RUNNING -ne 0 ]]; then
+	if [[ "${OS}" =~ (fedora|centos) ]] && [[ "${WG_RUNNING}" -ne 0 ]]; then
 		echo -e "\nWARNING: WireGuard does not seem to be running."
-		echo "Due to kernel mismatch issues on $OS, WireGuard might work if your system is out of date."
-		echo "You can check if WireGuard is running with: systemctl status wg-quick@$SERVER_WG_NIC"
+		echo "Due to kernel mismatch issues on ${OS}, WireGuard might work if your system is out of date."
+		echo "You can check if WireGuard is running with: systemctl status wg-quick@${SERVER_WG_NIC}"
 		echo 'If you get something like "Cannot find device wg0", please run:'
-		if [[ $OS == 'fedora' ]]; then
+		if [[ "${OS}" == 'fedora' ]]; then
 			echo "dnf update -y && reboot"
-		elif [[ $OS == 'centos' ]]; then
+		elif [[ "${OS}" == 'centos' ]]; then
 			echo "yum update -y && reboot"
 		fi
 	fi
@@ -206,22 +206,22 @@ function newClient() {
 	ENDPOINT="${SERVER_PUB_IP}:${SERVER_PORT}"
 
 	printf "\n"
-	until [[ "$CLIENT_WG_IPV4" =~ ^([0-9]{1,3}\.?){4}$ ]]; do
+	until [[ "${CLIENT_WG_IPV4}" =~ ^([0-9]{1,3}\.?){4}$ ]]; do
 		read -rp "Client's WireGuard IPv4: " -e -i "${SERVER_WG_IPV4::-1}"2 CLIENT_WG_IPV4
 	done
 
-	until [[ "$CLIENT_WG_IPV6" =~ ^([a-f0-9]{1,4}:?:?){3,5} ]]; do
+	until [[ "${CLIENT_WG_IPV6}" =~ ^([a-f0-9]{1,4}:?:?){3,5} ]]; do
 		read -rp "Client's WireGuard IPv6 : " -e -i "${SERVER_WG_IPV6::-1}"2 CLIENT_WG_IPV6
 	done
 
 	# Adguard DNS by default
-	until [[ $CLIENT_DNS_1 =~ ^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ ]]; do
+	until [[ "${CLIENT_DNS_1}" =~ ^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ ]]; do
 		read -rp "First DNS resolver to use for the client: " -e -i 176.103.130.130 CLIENT_DNS_1
 	done
-	until [[ $CLIENT_DNS_2 =~ ^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ ]]; do
+	until [[ "${CLIENT_DNS_2}" =~ ^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ ]]; do
 		read -rp "Second DNS resolver to use for the client (optional): " -e -i 176.103.130.131 CLIENT_DNS_2
-		if [[ $CLIENT_DNS_2 == "" ]]; then
-			CLIENT_DNS_2=$CLIENT_DNS_1
+		if [[ "${CLIENT_DNS_2}" == "" ]]; then
+			CLIENT_DNS_2="${CLIENT_DNS_1}"
 		fi
 	done
 
@@ -232,34 +232,34 @@ function newClient() {
 
 	# Generate key pair for the client
 	CLIENT_PRIV_KEY=$(wg genkey)
-	CLIENT_PUB_KEY=$(echo "$CLIENT_PRIV_KEY" | wg pubkey)
+	CLIENT_PUB_KEY=$(echo "${CLIENT_PRIV_KEY}" | wg pubkey)
 	CLIENT_PRE_SHARED_KEY=$(wg genpsk)
 
 	# Create client file and add the server as a peer
 	echo "[Interface]
-PrivateKey = $CLIENT_PRIV_KEY
-Address = $CLIENT_WG_IPV4/24,$CLIENT_WG_IPV6/64
-DNS = $CLIENT_DNS_1,$CLIENT_DNS_2
+PrivateKey = ${CLIENT_PRIV_KEY}
+Address = ${CLIENT_WG_IPV4}/24,${CLIENT_WG_IPV6}/64
+DNS = ${CLIENT_DNS_1},${CLIENT_DNS_2}
 
 [Peer]
-PublicKey = $SERVER_PUB_KEY
-PresharedKey = $CLIENT_PRE_SHARED_KEY
-Endpoint = $ENDPOINT
-AllowedIPs = 0.0.0.0/0,::/0" >>"$HOME/$SERVER_WG_NIC-client-$CLIENT_NAME.conf"
+PublicKey = ${SERVER_PUB_KEY}
+PresharedKey = ${CLIENT_PRE_SHARED_KEY}
+Endpoint = ${ENDPOINT}
+AllowedIPs = 0.0.0.0/0,::/0" >>"${HOME}/${SERVER_WG_NIC}-client-${CLIENT_NAME}.conf"
 
 	# Add the client as a peer to the server
 	echo -e "\n[Peer]
-PublicKey = $CLIENT_PUB_KEY
-PresharedKey = $CLIENT_PRE_SHARED_KEY
-AllowedIPs = $CLIENT_WG_IPV4/32,$CLIENT_WG_IPV6/128" >>"/etc/wireguard/$SERVER_WG_NIC.conf"
+PublicKey = ${CLIENT_PUB_KEY}
+PresharedKey = ${CLIENT_PRE_SHARED_KEY}
+AllowedIPs = ${CLIENT_WG_IPV4}/32,${CLIENT_WG_IPV6}/128" >>"/etc/wireguard/${SERVER_WG_NIC}.conf"
 
-	systemctl restart "wg-quick@$SERVER_WG_NIC"
+	systemctl restart "wg-quick@${SERVER_WG_NIC}"
 
 	echo -e "\nHere is your client config file as a QR Code:"
 
-	qrencode -t ansiutf8 -l L <"$HOME/$SERVER_WG_NIC-client-$CLIENT_NAME.conf"
+	qrencode -t ansiutf8 -l L <"${HOME}/${SERVER_WG_NIC}-client-${CLIENT_NAME}.conf"
 
-	echo "It is also available in $HOME/$SERVER_WG_NIC-client-$CLIENT_NAME.conf"
+	echo "It is also available in ${HOME}/${SERVER_WG_NIC}-client-${CLIENT_NAME}.conf"
 }
 
 function manageMenu() {
@@ -271,10 +271,10 @@ function manageMenu() {
 	echo "What do you want to do?"
 	echo "   1) Add a new user"
 	echo "   2) Exit"
-	until [[ $MENU_OPTION =~ ^[1-2]$ ]]; do
+	until [[ "${MENU_OPTION}" =~ ^[1-2]$ ]]; do
 		read -rp "Select an option [1-2]: " MENU_OPTION
 	done
-	case $MENU_OPTION in
+	case "${MENU_OPTION}" in
 	1)
 		newClient
 		;;