Fix quotation of further variables

Dockerfile

@@ -51,7 +51,7 @@ RUN \
         echo "$heading"; \
     }; \
     wget "${KEIL_URL}" --progress=bar:force:noscroll -O MDK537.exe; \
-    [ $DEBUG -eq 1 ] && { \
+    [ "$DEBUG" -eq 1 ] && { \
         mkdir -p logs; \
         mkdir -p screens; \
     } \
@@ -124,10 +124,10 @@ RUN \
                 [ "$x" -eq "$maxCount" ] && { pkill -9 MDK537.exe; mv "$logFile" "logs/timeout-try$try.log"; }; \
             } & \
         }; \
-        wait $pid; \
-        exitCode=$?; \
+        wait "$pid"; \
+        exitCode="$?"; \
         # Rename log file according to the state of the installer
-        [ $DEBUG -eq 1 ] \
+        [ "$DEBUG" -eq 1 ] \
         && [ -f "$logFile" ] \
         && { \
             # Move logs to location based on exit code
@@ -146,7 +146,7 @@ RUN \
         return "$exitCode"; \
     }; \
     display=:90; \
-    export DISPLAY=$display; \
+    export DISPLAY="$display"; \
     mkdir -p --mode=777 /tmp/.X11-unix; \
     # Create job for waiting for Xvfb to start
     watchStarting="$(mktemp)"; \