Improve script input

- Add a new option "--listenaddr" for specifying the IPv4 address
  that OpenVPN should listen on for requests. This can be useful
  in certain cases. If not specified, the script tries to auto
  detect the IPv4 address OpenVPN should listen on.
- Other minor improvements

openvpn-install.sh

@@ -146,6 +146,11 @@ parse_args() {
 				remove_ovpn=1
 				shift
 				;;
+			--listenaddr)
+				listen_addr="$2"
+				shift
+				shift
+				;;
 			--serveraddr)
 				server_addr="$2"
 				shift
@@ -203,17 +208,18 @@ check_args() {
 		fi
 	fi
 	if [ ! -e "$OVPN_CONF" ]; then
-		[ "$add_client" = 1 ] && exiterr "You must first set up OpenVPN before adding a client."
-		[ "$export_client" = 1 ] && exiterr "You must first set up OpenVPN before exporting a client."
-		[ "$list_clients" = 1 ] && exiterr "You must first set up OpenVPN before listing clients."
-		[ "$revoke_client" = 1 ] && exiterr "You must first set up OpenVPN before revoking a client."
+		st_text="You must first set up OpenVPN before"
+		[ "$add_client" = 1 ] && exiterr "$st_text adding a client."
+		[ "$export_client" = 1 ] && exiterr "$st_text exporting a client."
+		[ "$list_clients" = 1 ] && exiterr "$st_text listing clients."
+		[ "$revoke_client" = 1 ] && exiterr "$st_text revoking a client."
 		[ "$remove_ovpn" = 1 ] && exiterr "Cannot remove OpenVPN because it has not been set up on this server."
 	fi
 	if [ "$((add_client + export_client + revoke_client))" = 1 ] && [ -n "$first_client_name" ]; then
 		show_usage "Invalid parameters. '--clientname' can only be specified when installing OpenVPN."
 	fi
-	if [ -n "$server_addr" ] || [ -n "$server_proto" ] || [ -n "$server_port" ] \
-		|| [ -n "$first_client_name" ] || [ -n "$dns1" ]; then
+	if [ -n "$listen_addr" ] || [ -n "$server_addr" ] || [ -n "$server_proto" ] \
+		|| [ -n "$server_port" ] || [ -n "$first_client_name" ] || [ -n "$dns1" ]; then
 			if [ -e "$OVPN_CONF" ]; then
 				show_usage "Invalid parameters. OpenVPN is already set up on this server."
 			elif [ "$auto" = 0 ]; then
@@ -234,6 +240,12 @@ check_args() {
 			exiterr "Invalid client name, or client does not exist."
 		fi
 	fi
+	if [ -n "$listen_addr" ] && ! check_ip "$listen_addr"; then
+		show_usage "Invalid listen address. Must be an IPv4 address."
+	fi
+	if [ -n "$listen_addr" ] && [ -z "$server_addr" ]; then
+		show_usage "You must also specify the server address if the listen address is specified."
+	fi
 	if [ -n "$server_addr" ] && { ! check_dns_name "$server_addr" && ! check_ip "$server_addr"; }; then
 		exiterr "Invalid server address. Must be a fully qualified domain name (FQDN) or an IPv4 address."
 	fi
@@ -376,7 +388,8 @@ Options:
 Install options (optional):
 
   --auto                         auto install OpenVPN using default or custom options
-  --serveraddr [DNS name or IP]  server address, must be a fully qualified domain name (FQDN) or an IPv4 address.
+  --listenaddr [IPv4 address]    IPv4 address that OpenVPN should listen on for requests
+  --serveraddr [DNS name or IP]  server address, must be a fully qualified domain name (FQDN) or an IPv4 address
   --proto [TCP or UDP]           protocol for OpenVPN (TCP or UDP, default: UDP)
   --port [number]                port for OpenVPN (1-65535, default: 1194)
   --clientname [client name]     name for the first OpenVPN client (default: client)
@@ -396,8 +409,8 @@ show_welcome() {
 	else
 		show_header
 		op_text=default
-		if [ -n "$server_addr" ] || [ -n "$server_proto" ] || [ -n "$server_port" ] \
-			|| [ -n "$first_client_name" ] || [ -n "$dns1" ]; then
+		if [ -n "$listen_addr" ] || [ -n "$server_addr" ] || [ -n "$server_proto" ] \
+			|| [ -n "$server_port" ] || [ -n "$first_client_name" ] || [ -n "$dns1" ]; then
 			op_text=custom
 		fi
 		echo
@@ -524,6 +537,9 @@ check_nat_ip() {
 show_config() {
 	if [ "$auto" != 0 ]; then
 		echo
+		if [ -n "$listen_addr" ]; then
+			echo "Listen address: $listen_addr"
+		fi
 		if [ -n "$server_addr" ]; then
 			echo "Server address: $server_addr"
 		else
@@ -1363,6 +1379,7 @@ list_clients=0
 revoke_client=0
 remove_ovpn=0
 public_ip=""
+listen_addr=""
 server_addr=""
 server_proto=""
 server_port=""
@@ -1442,7 +1459,11 @@ if [[ ! -e "$OVPN_CONF" ]]; then
 	if [ "$auto" = 0 ]; then
 		enter_server_address
 	else
-		detect_ip
+		if [ -n "$listen_addr" ]; then
+			ip="$listen_addr"
+		else
+			detect_ip
+		fi
 		if [ -n "$server_addr" ]; then
 			public_ip="$server_addr"
 		else