Terminal can't execute files In CWD
If no path is given (either an absolute or a relative one) the shell searches through the directories listed in $PATH to find commands to execute. If the current directory isn't included there, you need to use a relative path like
./hulusubs_dl_osx

In theory you could solve this by adding . to PATH but this is considered bad practice due to the potential security risk (imagine somebody putting a fake ls command in one of your directories).