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


my $hash;

while (<DATA>){
	my ($left,$val) = split /=/,$_ or next;
	my ($first,@levels) = split /\./,$left;
    
	my $str="\$hash->{$first}";
	
	for my $last_level(@levels){
        $str .= "{$last_level}" 
	}
	eval "$str=$val";
}

print Dumper \$hash;

__DATA__
a.b='xyz'
a.c='abc'
d='def'
a.e='ghi'

##</code><code>##

$VAR1 = \{
            'a' => {
                     'e' => 'ghi',
                     'c' => 'abc',
                     'b' => 'xyz'
                   },
            'd' => 'def'
          };