#!/usr/bin/perl

use strict;
use warnings;

my $chunk1;
my $chunk2;
my $chunk3;

{
    local $/ = undef;
    (undef,$chunk1,$chunk2,$chunk3) = split(/^!(?:sectionname1|sectionname2|sectionname3)$/m, <DATA>);
}

print $chunk2;

__DATA__
!sectionname1
this is the data
!sectionname2
this is more data
!sectionname3
end