this should be faster. I forgot about sprintf.

box.sh

@@ -8,9 +8,8 @@ maxline == 1 {
 }
 
 function printtop () {
-	blank = ""
-	for (i = 0; i < maxlength + 4; i++)
-		blank = blank "*"
+	blank = sprintf("%*s", maxlength + 4, "")
+	gsub(" ", "*", blank)
 	printf("%s\n", blank)
 }