diff --git a/README.md b/README.md
index 0310dc32..163cf2cf 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ VPN_PASSWORD=your_vpn_password
 
 This will create a user account for VPN login, which can be used by your multiple devices[*](https://github.com/hwdsl2/docker-ipsec-vpn-server#multi-device-note) . The IPsec PSK (pre-shared key) is specified by the `VPN_IPSEC_PSK` environment variable. The VPN username is defined in `VPN_USER`, and VPN password is specified by `VPN_PASSWORD`.
 
-**Note:** In your `env` file, DO NOT put `""` or `''` around values, or add space around `=`. DO NOT use these characters within values: `\ " '`.
+**Note:** In your `env` file, DO NOT put `""` or `''` around values, or add space around `=`. DO NOT use these special characters within values: `\ " '`.
 
 All the variables to this image are optional, which means you don't have to type in any environment variable, and you can have an IPsec VPN server out of the box! Read the sections below for details.
 
diff --git a/run.sh b/run.sh
index 77b4d71f..930fad7c 100644
--- a/run.sh
+++ b/run.sh
@@ -20,12 +20,12 @@
 export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
 
 exiterr()  { echo "Error: $1" >&2; exit 1; }
-nospaces() { printf %s "$1" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//'; }
-noquotes() { printf %s "$1" | sed -e 's/^"\(.*\)"$/\1/' -e "s/^'\(.*\)'$/\1/"; }
+nospaces() { printf '%s' "$1" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//'; }
+noquotes() { printf '%s' "$1" | sed -e 's/^"\(.*\)"$/\1/' -e "s/^'\(.*\)'$/\1/"; }
 
 check_ip() {
   IP_REGEX='^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$'
-  printf %s "$1" | tr -d '\n' | grep -Eq "$IP_REGEX"
+  printf '%s' "$1" | tr -d '\n' | grep -Eq "$IP_REGEX"
 }
 
 if [ ! -f "/.dockerenv" ]; then
@@ -77,13 +77,13 @@ if [ -z "$VPN_IPSEC_PSK" ] || [ -z "$VPN_USER" ] || [ -z "$VPN_PASSWORD" ]; then
   exiterr "All VPN credentials must be specified. Edit your 'env' file and re-enter them."
 fi
 
-if printf %s "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" | LC_ALL=C grep -q '[^ -~]\+'; then
+if printf '%s' "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" | LC_ALL=C grep -q '[^ -~]\+'; then
   exiterr "VPN credentials must not contain non-ASCII characters."
 fi
 
 case "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" in
   *[\\\"\']*)
-    exiterr "VPN credentials must not contain the following characters: \\ \" '"
+    exiterr "VPN credentials must not contain these special characters: \\ \" '"
     ;;
 esac
 
@@ -99,7 +99,7 @@ PUBLIC_IP=${VPN_PUBLIC_IP:-''}
 
 # Check IP for correct format
 check_ip "$PUBLIC_IP" || PUBLIC_IP=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
-check_ip "$PUBLIC_IP" || exiterr "Cannot find valid public IP. Define it in your 'env' file as 'VPN_PUBLIC_IP'."
+check_ip "$PUBLIC_IP" || exiterr "Cannot detect this server's public IP. Define it in your 'env' file as 'VPN_PUBLIC_IP'."
 
 L2TP_NET=${VPN_L2TP_NET:-'192.168.42.0/24'}
 L2TP_LOCAL=${VPN_L2TP_LOCAL:-'192.168.42.1'}
@@ -201,8 +201,6 @@ EOF
 
 # Create VPN credentials
 cat > /etc/ppp/chap-secrets <<EOF
-# Secrets for authentication using CHAP
-# client  server  secret  IP addresses
 "$VPN_USER" l2tpd "$VPN_PASSWORD" *
 EOF
 
@@ -213,7 +211,6 @@ EOF
 
 # Update sysctl settings
 SYST='/sbin/sysctl -e -q -w'
-
 if [ "$(getconf LONG_BIT)" = "64" ]; then
   SHM_MAX=68719476736
   SHM_ALL=4294967296
@@ -221,12 +218,10 @@ else
   SHM_MAX=4294967295
   SHM_ALL=268435456
 fi
-
 $SYST kernel.msgmnb=65536
 $SYST kernel.msgmax=65536
 $SYST kernel.shmmax=$SHM_MAX
 $SYST kernel.shmall=$SHM_ALL
-
 $SYST net.ipv4.ip_forward=1
 $SYST net.ipv4.conf.all.accept_source_route=0
 $SYST net.ipv4.conf.all.accept_redirects=0
diff --git a/vpn.env.example b/vpn.env.example
index a33db51d..21bf4ebf 100644
--- a/vpn.env.example
+++ b/vpn.env.example
@@ -1,6 +1,6 @@
 # Define your own values for these variables
 # - DO NOT put "" or '' around values, or add space around =
-# - DO NOT use these characters within values: \ " '
+# - DO NOT use these special characters within values: \ " '
 VPN_IPSEC_PSK=your_ipsec_pre_shared_key
 VPN_USER=your_vpn_username
 VPN_PASSWORD=your_vpn_password