--- a/mallard-ducktype-1.0.2/tests/runtests
+++ b/mallard-ducktype-1.0.2/tests/runtests
@@ -8,19 +8,20 @@
 silent=0
 glob=""
 
-for arg in $@; do
-    if [ "x$arg" = "x-s" ]; then
+for arg do
+    if [ "$arg" = "-s" ]; then
         silent=1
-    elif [ "x$arg" != "x" ]; then
+    elif [ -n "$arg" ]; then
         glob="$arg"
     fi
 done
 
 for duck in *$glob*.duck; do
+    [ -f "$duck" ] || continue
     count=$(( count + 1 ))
-    out=$(echo $duck | sed -e 's/\.duck$/.out/')
-    page=$(echo $duck | sed -e 's/\.duck$/.page/')
-    error=$(echo $duck | sed -e 's/\.duck$/.error/')
+    out=${duck%.duck}.out
+    page=${duck%.duck}.page
+    error=${duck%.duck}.error
     fail=""
     if [ -f "$page" ]; then
         python3 runtest.py "$duck" > "$out" || fail="exit status $?"
@@ -29,7 +30,6 @@
             diff -u "$out" "$page" >&2 || :
         fi
     elif [ -f "$error" ]; then
-        status=0
         python3 runtest.py "$duck" > "$out" || :
         if ! cmp "$out" "$error" >&2; then
             fail="unexpected error message"
@@ -39,7 +39,7 @@
         fail="neither $page nor $error exists"
     fi
     if [ -z "$fail" ]; then
-        if [ $silent = 0 ]; then
+        if [ "$silent" = 0 ]; then
             echo "ok $count - $duck"
         fi
     else