Hi, I have my script written in perl format, but the idea should be equally well applied to other script format you may want to use. .... $sim = '/home/syan/ns2/ns-2.1b4-current/ns'; for ($i=0; $i < 100; $i++) { $cmdLine2 = $sim . " " . "$workdir1/example.tcl"; } .... .... I think it should work for you, try it out! shuqian