my $limit = 100;
my $file  = 'big.file';

sub tail {
    my $lim = $limit;

    my @alpha;
    my @beta;
    my $current = \@alpha;

    open( IN, $file ) or die "Cannot open $file for input: $!\n";
    while( <IN> ) {
        push @$current, $_;
        if( scalar @$current > $limit ) {
            if( $current == \@alpha ) {
                @beta = ();
                $current = \@beta;
            }
            else {
                @alpha = ();
                $current = \@alpha;
            }
        }
    }
    close IN;

    return @{$current == \@alpha ? \@beta : \@alpha}[-($limit - scalar @$current)..-1],
        @$current;
}