system("mysqldump","--add-drop-table","-uroot","-ppassword", "mydatabase","|","gzip","-9c",">","$backup_dir/mydatabase.sql.gz");

##</code><code>##

mysqldump '-add-drop-table' '-uroot '-ppassword' 'mydatabase' '|' 'gzip' '-9c' '>' "$backup_dir/mydatabase.sql.gz"

##</code><code>##

use IPC::Open3 qw( open3 );

{
   local *FROM_MYSQLDUMP;
   open(local *INPUT,  '<', '/dev/null') or die $!;
   open(local *OUTPUT, '>', "$backup_dir/mydatabase.sql.gz") or die $!;

   my $mysqldump_pid = open3('<&INPUT', \*FROM_MYSQLDUMP, '>&STDERR',
      mysqldump => (
         '--add-drop-table',
         '-u'.'root',
         '-p'.'password',
         'mydatabase',
      ),
   );

   my $gzip_pid = eval {
      open3('<&FROM_MYSQLDUMP', '>&OUTPUT', '>&STDERR',
         gzip => ( '-9c' ),
      )
   };   

   if (!$gzip_pid) {
      my $e = $@;
      kill(KILL => $mysqldump_pid);
      waitpid($mysqldump_pid, 0);
      die($e);
   }
   
   waitpid($mysqldump_pid, 0);
   waitpid($gzip_pid, 0);
}

##</code><code>##

sub text_to_shell_lit(_) {
   return $_[0] if $_[0] =~ /^[a-zA-Z0-9_\-]+\z/;
   my $s = $_[0];
   $s =~ s/'/'\\''/g;
   return "'$s'";
}

my $mysqldump_cmd = join ' ', map text_to_shell_lit,
   mysqldump => (
      '--add-drop-table',
      '-u'.'root',
      '-p'.'password',
      'mydatabase',
   );

my $gzip_cmd = join ' ', map text_to_shell_lit,
   gzip => ( '-9c' );
   
my $output_file_lit = text_to_shell_lit("$backup_dir/mydatabase.sql.gz");
   
system("$mysqldump_cmd | $gzip_cmd > $output_file_lit");