use strict;
use warnings;

my @arr = (2,7,12,5,17,9);
print max(@arr);

sub max {
    my $max = $_[0];
    do { $max = $_[$_] if $max < $_[$_]; } for 1..$#_;
    $max;
}

##</code><code>##

my $max = (sort { $b <=> $a } @arr)[0];