open(FH, "$Exec_Cmd 2>&1 |");
while (<FH>)
{
  print $_; # I have STDERR captured in $_ but then this 
            # does not handle STDIN  
  
}

##</code><code>##

open(FH, "$Exec_Cmd 0>&2 |");
while (<FH>)
{
  print $_; # I take care of STDIN but then this 
            # does not handle STDERR  
  
}