diff --git a/data/tools/unit_tree/update-wmlunits b/data/tools/unit_tree/update-wmlunits
index bb1e4ac4616b..4b8c01558308 100755
--- a/data/tools/unit_tree/update-wmlunits
+++ b/data/tools/unit_tree/update-wmlunits
@@ -7,56 +7,54 @@ set -e -u
 # PORT=1.12.x
 
 # must run from the correct directory
-DIR="$(dirname $0)"
+dir="$(dirname "$0")"
 
 EXTRA_ADDON_OPTIONS=${EXTRA_ADDON_OPTIONS:-}
 EXTRA_WMLUNITS_OPTIONS=${EXTRA_WMLUNITS_OPTIONS:-}
 TIMEOUT=${TIMEOUT:-20}
 SOURCES=${SOURCES:-/usr/src/wesnoth}
-ADDONS=$DIR/addons
-EXE=$DIR/wesnoth
-CONFIG=$DIR/config
-SRC=$SOURCES/$VERSION
-DATA=$SRC
-LOG=$DIR/logs
-TMPOUT=$DIR/output
+addons=$dir/addons
+exe=$dir/wesnoth
+config=$dir/config
+src=$SOURCES/$VERSION
+data=$src
+log=$dir/logs
+tmpout=$dir/output
 OUT=${OUT:-"/srv/www/html/units/$VERSION"}
-TRANS=$DIR/translations
-BUILD=$DIR/build
+trans=$dir/translations
+build=$dir/build
 # always using the master version
 TOOLS=${TOOLS:-$SOURCES/master/data/tools}
-export TEMP=$DIR/temp
+export TEMP=$dir/temp
 
 # in case there's leftovers from a previous run
-rm -rf $CONFIG/data/add-ons
-rm -rf $TMPOUT
+rm -rf "$config/data/add-ons"
+rm -rf "$tmpout"
+rm -rf "$TEMP"
 
-mkdir -p $CONFIG/data/add-ons
-mkdir -p $ADDONS
-mkdir -p $LOG
-mkdir -p $TMPOUT
-mkdir -p $TEMP
-mkdir -p translations
-
-rm -rf $TEMP/*
+mkdir -p "$config/data/add-ons"
+mkdir -p "$addons"
+mkdir -p "$log"
+mkdir -p "$tmpout"
+mkdir -p "$TEMP"
+mkdir -p "$trans"
 
 # we only need the parser, but have to build the game executable for that
 echo BUILDING
-cd $DIR # the scons build places the wesnoth executable in the current directory
-TRAVIS=1 TRAVIS_OS_NAME=Linux scons -Y "$SRC" --option-cache="$BUILD/.scons-option-cache"
+cd "$dir" || exit # the scons build places the wesnoth executable in the current directory
+TRAVIS=1 TRAVIS_OS_NAME=Linux scons -Y "$src" --option-cache="$build/.scons-option-cache"
 
 # later can just rebuild updated campaigns, but for now rebuild everything
-rm -f $DIR/overview.txt
+rm -f "$dir/overview.txt"
 
 echo DOWNLOADING
-$TOOLS/wesnoth_addon_manager -p $PORT -d '.*' -c $ADDONS $EXTRA_ADDON_OPTIONS > $LOG/wesnoth_addon_manager.txt 2>&1
+"$TOOLS/wesnoth_addon_manager" -p "$PORT" -d '.*' -c "$addons" $EXTRA_ADDON_OPTIONS > "$log/wesnoth_addon_manager.txt" 2>&1
 echo WORKING
-python3 -u $TOOLS/wmlunits -t $TRANS -D $DATA -o $TMPOUT -w $EXE \
-    -C $CONFIG -a $ADDONS -L $DIR/overview.txt -B $DIR/overview.txt \
-    -T $TIMEOUT $EXTRA_WMLUNITS_OPTIONS > $LOG/wmlunits.txt 2>&1
-test -f $TMPOUT/mainline/en_US/mainline.html
-test -f $TMPOUT/'pics/core$images$units$woses$wose.png'
-rsync -vaz --delete $TMPOUT/ $OUT > $LOG/rsync.txt 2>&1
-rm -rf $TEMP/*
-rm -rf $TMPOUT
-
+python3 -u "$TOOLS/wmlunits" -t "$trans" -D "$data" -o "$tmpout" -w "$exe" \
+    -C "$config" -a "$addons" -L "$dir/overview.txt" -B "$dir/overview.txt" \
+    -T "$TIMEOUT" $EXTRA_WMLUNITS_OPTIONS > "$log/wmlunits.txt" 2>&1
+test -f "$tmpout"/mainline/en_US/mainline.html
+test -f "$tmpout"/'pics/core$images$units$woses$wose.png'
+rsync -vaz --delete "$tmpout/" "$OUT" > "$log/rsync.txt" 2>&1
+rm -rf "$TEMP"
+rm -rf "$tmpout"