If I understand you correctly, you need something like this:

foreach (@members_name) {
  if (/^${accountnumber}_/) {
    to_sub($zip, $accountnumber, $_ );

  }
}
[download]

If that is what you want, you could speedup this segment a bit if you stored the names in a hash:

foreach my $member ($zip->members()) { # print file information
      my $member_file_name = $member->fileName();
      my ($acc)= $member_file_name=~/^\d+/;
      push @{$members_name{$acc}}, $member_file_name;
}

...
  if (exists $members_name{$accountnumber)) {
    foreach (@{$members_name{$accountnumber}) {
      to_sub( $zip, $accountnumber, $_ );
[download]