Use builtin arithmetic expansion feature to replace external expr command to triger tst.sh in parallel ASAP

Author: zhulipeng

UnixBench/pgms/multi.sh

@@ -17,7 +17,7 @@ ID="@(#)multi.sh:3.4 -- 5/15/91 19:30:24";
 instance=1
 while [ $instance -le $1 ]; do
 	/bin/sh "$UB_BINDIR/tst.sh" &
-	instance=`expr $instance + 1`
+	instance=$(($instance + 1))
 done
 wait