my $message= '';
while( <> ) {
    if( ! /^\d{4}-\d\d-\d\d / ) {
        $message .= $_;
    } else {
        print $message
            if(  $message  =~ /keyword/  );
        $message= $_;
    }
}
print $message
    if(  $message  =~ /keyword/  );