use strict;
use warnings;

open (NEW, ">", "output.txt" ) or die "could not open:$!";

my $find = 'COMPUTER1';
my $inside = 0;
my $data = '';
while (<DATA>) {
    next if (/^$/);
    $inside = 1 if /COMPUTER1/;
    if ($inside){
        $inside=0;
        next;
    }
    else{
        $data .= $_;
        print NEW $_
}
}
print '[' . $data . ']';

close(NEW)
__DATA__

COMPUTER1

ACCT1
ACCT2
ACCT3

COMPUTER1

ACCT4
ACCT7
ACCT8
ACCT9