diff --git a/docs/ikev2-howto-zh.md b/docs/ikev2-howto-zh.md
index dd79ba3..2f87c9b 100644
--- a/docs/ikev2-howto-zh.md
+++ b/docs/ikev2-howto-zh.md
@@ -25,7 +25,7 @@ Libreswan 支持通过使用 RSA 签名算法的 X.509 Machine Certificates 来
 
    ```bash
    $ PUBLIC_IP=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
-   $ echo "$PUBLIC_IP"
+   $ printf '%s' "$PUBLIC_IP"
    （检查显示的公共 IP）
    ```
 
diff --git a/docs/ikev2-howto.md b/docs/ikev2-howto.md
index 787ce74..8550699 100644
--- a/docs/ikev2-howto.md
+++ b/docs/ikev2-howto.md
@@ -25,7 +25,7 @@ Before continuing, make sure you have successfully <a href="https://github.com/h
 
    ```bash
    $ PUBLIC_IP=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
-   $ echo "$PUBLIC_IP"
+   $ printf '%s' "$PUBLIC_IP"
    (Check the displayed public IP)
    ```
 
diff --git a/extras/vpnupgrade.sh b/extras/vpnupgrade.sh
index 871ba81..93bb86e 100644
--- a/extras/vpnupgrade.sh
+++ b/extras/vpnupgrade.sh
@@ -24,8 +24,8 @@ vpnupgrade() {
 
 os_type="$(lsb_release -si 2>/dev/null)"
 if [ -z "$os_type" ]; then
-  [ -f /etc/os-release  ] && os_type="$(. /etc/os-release  && echo "$ID")"
-  [ -f /etc/lsb-release ] && os_type="$(. /etc/lsb-release && echo "$DISTRIB_ID")"
+  [ -f /etc/os-release  ] && os_type="$(. /etc/os-release  && printf '%s' "$ID")"
+  [ -f /etc/lsb-release ] && os_type="$(. /etc/lsb-release && printf '%s' "$DISTRIB_ID")"
 fi
 if ! printf '%s' "$os_type" | head -n 1 | grep -qiF -e ubuntu -e debian -e raspbian; then
   exiterr "This script only supports Ubuntu and Debian."
diff --git a/vpnsetup.sh b/vpnsetup.sh
index 485c599..bc24ffc 100755
--- a/vpnsetup.sh
+++ b/vpnsetup.sh
@@ -50,8 +50,8 @@ vpnsetup() {
 
 os_type="$(lsb_release -si 2>/dev/null)"
 if [ -z "$os_type" ]; then
-  [ -f /etc/os-release  ] && os_type="$(. /etc/os-release  && echo "$ID")"
-  [ -f /etc/lsb-release ] && os_type="$(. /etc/lsb-release && echo "$DISTRIB_ID")"
+  [ -f /etc/os-release  ] && os_type="$(. /etc/os-release  && printf '%s' "$ID")"
+  [ -f /etc/lsb-release ] && os_type="$(. /etc/lsb-release && printf '%s' "$DISTRIB_ID")"
 fi
 if ! printf '%s' "$os_type" | head -n 1 | grep -qiF -e ubuntu -e debian -e raspbian; then
   exiterr "This script only supports Ubuntu and Debian."
diff --git a/vpnsetup_centos.sh b/vpnsetup_centos.sh
index 2d5656b..938cc89 100755
--- a/vpnsetup_centos.sh
+++ b/vpnsetup_centos.sh
@@ -423,6 +423,7 @@ else
   systemctl --now mask firewalld 2>/dev/null
   systemctl enable iptables fail2ban 2>/dev/null
 fi
+
 if ! grep -qs "hwdsl2 VPN script" /etc/rc.local; then
   if [ -f /etc/rc.local ]; then
     conf_bk "/etc/rc.local"