Outside of a *subroutine*, the default variable for list operations is @ARGV. Inside a subroutine, it's @_. Since none of your code occurs inside a subroutine, it's all attempting to operate on @ARGV.

Note, though, that while @_ is a respectable global, the @_ your subroutine sees is local to the subroutine. So unless you *explicitly* pass arguments to the subroutine, what you set @_ outside the subroutine won't make any valuables (update or, indeed, *values* =) available to the subroutine. i.e. :

sub jah {
        while (my $d = shift) {
             print "$d\n";
        }
}
@_ = qw(foo bar bat);
jah(); # produces no output
jah(qw(foo bar bat)); # produces output
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HTH

perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n"; *other_name = *rose; print "$oth
+er_name\n"'
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