add function to get default route ipv4

functions.sh

@@ -78,6 +78,37 @@ ensure_variables_are_defined () {
   done
 }
 
+# check if IPv4 syntax is valid
+check_valid_ipv4() {
+    re='^((1?[0-9]{1,2}|2([0-4][0-9]|5[0-5]))\.){3}'
+    re+='(1?[0-9]{1,2}|2([0-4][0-9]|5[0-5]))$'
+
+    if [[ ${1} =~ ${re} ]]; then
+	return 0
+    else
+	echo "ERROR : ${1} is not a valid IPv4 address"
+	exit 1
+    fi
+}
+
+# Get default interface IPv4 address
+# and return result in variable passed as argument
+get_default_iface_ipv4() {
+    # Call this function with the name of the variable
+    # you want to store the result in :
+    # default_iface_ipv4 myipv4
+    # See https://www.linuxjournal.com/content/return-values-bash-functions
+    local __resultvar=${1}
+    local __default_iface=$(awk '$2 == 00000000 { print $1 }' /proc/net/route)
+    local __default_iface_ipv4=$(ip addr show dev "${__default_iface}" | awk '$1 == "inet" { sub("/.*", "", $2); print $2 }')
+    if check_valid_ipv4 ${__default_iface_ipv4}; then
+	eval $__resultvar="'${__default_iface_ipv4}'"
+	return 0
+    else
+	exit 1
+    fi
+}
+
 # ok if systemd unit file {1} exists
 ensure_systemd_unit_exists () {
     if ! check_systemd_unit_exists ${1}; then