use IPC::Open3 qw( open3 );

while (my $client = $socket->accept()) { 
   while (<$client>) { 
      chomp; 
      my ($cmd, @args) = split(/:/, $_); 

      my @cmd;
      if ($cmd eq 'ls') {
         @cmd = ( 'ls', '-s', '--', @args );
      }

      if (@cmd) {
         open(local *C_STDIN,  '<', '/dev/null') or die;
         open(local *C_STDOUT, '>&, $client) or die;
         my $pid = open3('<C_STDIN', '>C_STDOUT', '>C_STDOUT', @cmd);
         waitpid($pid, 0);
      }
   }
}