#!/user/bin/env perl

use strict;
use warnings;
use Data::Dumper;

my @array = qw(a b c d e f g h i 123);
my $recurse_level = 0;

sub to_hash {
  my $hash_ref = shift;
  my @array = @_; 
  my $array_count = @array;
  die "Need at least 2 elements in original array" if (0 == $recurse_level && 2 > $array_count);
  my $index;
  if (2 < $array_count) {
    $index = shift @array;
    $recurse_level++;
    $hash_ref->{$index} = to_hash({},@array);
  }   
  else {
    $index = shift @array;
    $hash_ref->{$index} = shift @array;
  }
  return $hash_ref;
}

my $hash_ref = to_hash({},@array); 

print Dumper($hash_ref);