Fix against POSIX standard.

dnsapi/dns_duckdns.sh

@@ -17,8 +17,7 @@ dns_duckdns_add() {
   txtvalue=$2
 
   # We'll extract the domain/username from full domain
-  IFS='.' read -r -a fqdn <<< "$fulldomain"
-  DuckDNS_domain="${fqdn[-3]}"
+  DuckDNS_domain=$(printf "%s\n" "$fulldomain" | rev | cut -d \. -f 3 | rev)
 
   if [ -z "$DuckDNS_domain" ]; then
     _err "Error extracting the domain."
@@ -42,7 +41,7 @@ dns_duckdns_add() {
 
   # Now add the TXT record to DuckDNS
   _info "Trying to add TXT record"
-  if _duckdns_rest GET "$API_Params&txt=$txtvalue" && [ $response == "OK" ]; then
+  if _duckdns_rest GET "$API_Params&txt=$txtvalue" && [ "$response" -eq "OK" ]; then
     _info "TXT record has been successfully added to your DuckDNS domain."
     _info "Note that all subdomains under this domain uses the same TXT record."
     return 0
@@ -60,7 +59,7 @@ dns_duckdns_rm() {
 
   # Now remove the TXT record from DuckDNS
   _info "Trying to remove TXT record"
-  if _duckdns_rest GET "$API_Params&txt=&clear=true" && [ $response == "OK" ]; then
+  if _duckdns_rest GET "$API_Params&txt=&clear=true" && [ "$response" -eq "OK" ]; then
     _info "TXT record has been successfully removed from your DuckDNS domain."
     return 0
   else
@@ -80,7 +79,7 @@ _duckdns_rest() {
   _debug url "$url"
 
   # DuckDNS uses GET to update domain info
-  if [ $method == "GET" ]; then
+  if [ "$method" -eq "GET" ]; then
     response="$(_get "$url")"
   else
     _err "Unsupported method"