The error message says that /pptai/nightly_db/api.out does not exist. So likely, the file /pptai/nightly_db/api.out does not exist. Which, by induction, would mean that the command perl -n /tmp/test.pl $test_input > /pptai/nightly_db/api.out failed. You don't capture the error output of your command, so it's kinda hard to tell why the file is not created, but most likely, that is a permissions issue, likely because the user your script is running under is not the user that is allowed to access /tmp/test.pl or something like that. Look in your webserver error log for further information.