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

my @structure;
my %temp;

while (<DATA>)
{     
   if (!/\S/)     # blank line ends a record
   { 
       push (@structure, {%temp}) if (%temp); # possible null record
       %temp=(); 
   } 
   else
   {
       chomp;
       my ($key, $value) = split /\s+=>\s+/,$_;
       $value =~ tr/"//d;   # remove double quotes
       $temp{$key}=$value;
   }     
}
push (@structure, {%temp}) if (%temp); # possible last record
print Dumper \@structure;

=Output
$VAR1 = [
          {
            'a' => 'premiere valeur',
            'b' => 'some value',
            'index' => '1',
            'z' => 'dernier mot',
            'objet' => 'fin'
          },
          {
            'a' => 'autre valeur',
            'index' => '77',
            'objet' => 'fin',
            'z' => 'aurai-je le dernier mot ?'
          }
        ];

=cut


__DATA__

objet => debut
index => 1
a => "premiere valeur"
b => "some value"
z => "dernier mot"
objet => fin

objet => debut
index => 77
a => "autre valeur"
z => "aurai-je le dernier mot ?"
objet => fin