#! perl -w

unshift @array, $_ for 1..20;

@array3=sort({($b/5) <=> ($a/5)}@array);

foreach (@array3)
{
print "$_ ";
}

@array3=sort({$b/5 <=> $a/5}@array);

use strict;
use warnings;

my @array = (1..20);
my @array3 = sort { $a % 5 <=> $b % 5 } @array;
print @array3;

my @array3 = sort { $a <=> $b } map { $_ % 5 } @array;

my @array3 = sort { $a <=> $b } map { $_ %= 5 } @array;

use warnings;
use strict;

my @array = (1..20);
my @array3 = sort { $a <=> $b } map { $_ % 5 } @array;
print join(', ', @array3);