test.pl

foo('bar', 100)

sub foo {
    # $first = 'bar'
    my $first = shift;
    my $first = shift @_;
    my $first = $_[0];
    my ($first) = @_;

    # $first = 'bar', $second = 100;
    my $first = shift; 
    my $second = shift;

    my $first  = $_[0];
    my $second = $_[1];

    my ($first, $second) = @_;
}