use warnings;
use strict;

$/ = "_END=======\n";

while (<DATA>) {
    s/========KEYWORD.+\n//g;
    print '-' x 80, $_, '-' x 80;
}

__DATA__

========KEYWORD 1===========
Text
text
text
========KEYWORD 1_END=======


========KEYWORD 2===========
Text
text
text
========KEYWORD 2_END=======


========KEYWORD 3===========
Text
text
text
========KEYWORD 3_END=======