Answers above hint at the simplest solution, without actually giving it. Try this:

$cmd ="tar -cvvCf $UploadDir $UploadDir/results.tar en_ran.out en-ave.
+out en_ave_ran.out gc-ave.out score_ran.out score-ave_ran.out score-a
+ve.out";
[download]

(Later) Oops, gamache gave the correct solution.