@_ gets set to the parameters passed to a function call, not for the command line parameters. For that you use @ARGV:

$ perl -e 'print @_;print "::\n";print @ARGV;' camel
::
camel
[download]

To get the number of parameters, you use @ARGV in scalar context:

$ perl -e ''print scalar @ARGV;' my camel
2
[download]

CU
Robartes-