config file checks and sample config

Changed the way the existence of config files is checked. It may be a
bit slower than before when there are many config files but maybe it
avoids other trouble.
Updated the sample config.

nsupdate.d/sample.config.dist

@@ -5,9 +5,16 @@ IP_CHECK_SITE="https://ip.dblx.io"
 
 # use drill instead of nslookup for hostname lookup
 USE_DRILL="YES"
+
+# Use IPv6 connection
 IPV6="NO"
+
+# Update an MX record
 MX="NO"
 
+# Suppress all messages
+SILENT=NO
+
 # Login credentials for the inwx admin interface
 INWX_USER="USERNAME"
 INWX_PASS='PASSWORD'

nsupdate.sh

@@ -24,23 +24,17 @@
 # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-##################
-# check required #
-##################
+# check required tools
 command -v curl >/dev/null 2>&1 || { echo >&2 "I require curl but it's not installed. Note: all needed items are listed in the README.md file."; exit 1; }
 command -v awk >/dev/null 2>&1 || { echo >&2 "I require awk but it's not installed. Note: all needed items are listed in the README.md file."; exit 1; }
 command -v drill >/dev/null 2>&1 || command -v nslookup >/dev/null 2>&1 || { echo >&2 "I need drill or nslookup installed. Note: all needed items are listed in the README.md file."; exit 1; }
-##################
-# check config   #
-##################
-configfiles=$(shopt -s nullglob dotglob; echo nsupdate.d/*.config)
-if (( ! ${#configfiles} ));then
-    echo "There does not seem to be any config file available." ; exit 1;
-fi
-##################
 
 LOG=$0.log
 SILENT=NO
+
+# Check if there are any usable config files
+if ls $(dirname $0)/nsupdate.d/*.config 1> /dev/null 2>&1; then
+   
    # Loop through configs
    for f in $(dirname $0)/nsupdate.d/*.config
    do
@@ -137,3 +131,6 @@ do
       unset INWX_USER
       unset INWX_DOMAIN_ID
    done
+else
+   echo "There does not seem to be any config file available in $(dirname $0)/nsupdate.d/." ; exit 1;
+fi