Can you pass a reference to ARGV and get it to work on that?

use Carp;

my_main(\@ARGV);

sub my_main
{
  my $first = shift @{$_[0]};
  carp "Rubbish\n";
  exit;
}
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That gets rid of the error, but I don't know how much of an impact that will have on the rest of your code.

Otherwise, why don't you just say:

  my_main() unless caller();
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@ARGV is, after all, a global, you don't have to pass it as a parameter. If you want to munge it non-destructively, localise it with local @ARGV = @ARGV.