#original seq

accgttac

#required output
acc         #first substring
ccg
cgt
tta
tac         #fifth substring

##</code><code>##

#!/usr/local/bin/perl
use strict;
use warnings;

for(<DATA>){
              print substr ($_,0,3),"\n" ;

              }

__DATA__
accgttac

##</code><code>##

use warnings;
use strict;

my $aoh = [
            {
              first => 1,
              second => ['foo', 'bar', 'baz',],
            },
            {
              first => 2,
              second => ['foz', 'barz',],
            },
            {
              first => 2,
              second => ['frip', 'barn', 'bazurt',],
            },
            {
              first => 1,
              second => ['foo',],
            },
          ];

# use a subroutine to pass a custom
# sort code block
@$aoh = sort by_custom @$aoh;

######## subs ########
sub by_custom{
  return (  # sort on first key - numeric ascending
           ( $a->{first} <=> $b->{first} )
          ||
           ( # then by the size of the second key
             scalar@{$b->{second} } 
              <=> 
             scalar@{ $a->{second} } 
           )
          );
}