my $file = '/scripts/clients';
open(my $fh, '<', $file)
   or die("Unable to open file \"$file\": $!\n");

my $hostname;
my @dirs;

while (<$fh>) {
   chomp;

   if (/^\[/) {
      backup($client, \@dirs) if defined($hostname);

      s/^\[//; s/\]$//;
      $hostname = $_;
      @dirs = ();
   } else {
      s/^"//; s/"$//;
      push @dirs, $_;
   }
}

backup($client, \@dirs) if defined($hostname);