For cases like these, you can either do:

my $location = shift @ARGV or die "usage: $0 [filename]\n";
[download]

or, if you want a default,

my $location = shift || 'default value';
[download]

Minor amplification shift called without an explicit argument will return the next element of @ARGV if it is called outside a subroutine, and returns the next element of @_ if called within a subroutine.

HTH

Philosophy can be made out of anything. Or less -- Jerry A. Fodor