use strict;
use warnings;

my $part = 0;

while (<DATA>){
	chomp $_;
	if ( $_ =~ /objet => debut$/ .. /objet => fin$/){
		print "TRUE\n";
		if ( /objet => debut$/ ){
			next;    # we skip the opening tag
		}
		elsif ( /objet => fin$/ ){
			$part++; # we increment our index $part on closing tag
		}
		else{
			print "\tPART $part: [$_]\n"; # here is the meat: do what you need
		}
	}
	else{
		print "FALSE for line: [$_]\n"; 
	}
}

__DATA__
objet => debut
index => 1
a => "premiere valeur"
z => "dernier mot"
objet => fin
ALIEN LINE AFTER fin
objet => debut
index => 77
a => "autre valeur"
z => "aurai-je le dernier mot ?"
objet => fin

##</code><code>##

TRUE
TRUE
        PART 0: [index => 1]
TRUE
        PART 0: [a => "premiere valeur"]
TRUE
        PART 0: [z => "dernier mot"]
TRUE
FALSE for line: [ALIEN LINE AFTER fin]
TRUE
TRUE
        PART 1: [index => 77]
TRUE
        PART 1: [a => "autre valeur"]
TRUE
        PART 1: [z => "aurai-je le dernier mot ?"]
TRUE