use strict;
use warnings;

use Data::Dumper;

my $keyword;
my %text_of;
while (<DATA>) {
    if ( defined $keyword && /^={8}\Q$keyword\E_END={5}/ ) {
        undef $keyword;
        next;
    }
    if ( /^={8}([^=]+)={5}/ ) {
        $keyword = $1;
        next;
    }
    $text_of{ $keyword } .= $_ if defined $keyword;
}
print Dumper \%text_of;

__DATA__
========KEYWORD 1===========
key 1 Text 1
key 1 text 2
key 1 text 3
========KEYWORD 1_END=======


========KEYWORD 2===========
key 2 Text 1
key 2 text 2
key 2 text 3
========KEYWORD 2_END=======


========KEYWORD 3===========
key 3 Text 1
key 3 text 2
key 3 text 3
========KEYWORD 3_END=======