push (@Mdevices, [$UnitID, $fileno]);
for ($k=0; $k<=$#Mdevices; $k++)
  {
    print $Mdevices[$k][0],"\n";
  }
  $k=0;

##</code><code>##

  my @Mdevices ;
  my @Cdevices ;
  while (... something ...) {
    ... do something to get $UnitID & $fileno ...

    push (@Cdevices, $UnitID, $fileno);

    ... do some other stuff ...

    push (@Mdevices, \@Cdevices);
  } ;

##</code><code>##

  my @Mdevices ;
  while (... something ...) {
    my @Cdevices ;
    ... do something to get $UnitID & $fileno ...

    push (@Cdevices, $UnitID, $fileno);

    ... do some other stuff ...

    push (@Mdevices, \@Cdevices);
  } ;

##</code><code>##

  my @Mdevices ;
  while (... something ...) {
    ... do something to get $UnitID & $fileno ...

    ... do some other stuff ...

    push (@Mdevices, [$UnitID, $fileno]);
  } ;