Q:

How to write output in TraditionalForm into external text files? 

I'd like to write output in TraditionalForm into external text files ofile.txt.   I tried to use
s = OpenWrite["/home/tigerhead/log/ofile.txt", FormatType -> TraditionalForm];
$Output = s;
<run various Mathematica programs>
Close[s];

but get errors:
Intersection::normal: 
   Nonatomic expression expected at position 2 in 
    Intersection[{StandardForm, TraditionalForm}, FormatType]. 
Options::optnf: 
   FormatType is not a known option for 
    Intersection[OutputStream[/home/tigerhead/log/ofile.txt, 21], {OutputStream[/home/tigerhead/log/ofile.txt, 20], OutputStream[stdout, 1], 
      OutputStream[stderr, 2], OutputStream[/home/tigerhead/<<38>>.txt, 
       21], stdout, stderr}]. 

Any one has a clue? 

A:

Not a full solution, but to get rid of the error you could try setting (note the curly brackets) 
$Output = {s} 

or even 
$Output = Append[$Output, s] 

if you want the output to be printed to sdout as well.  Note that this still writes expressions to the file in OutputFormat by default even with FormatType -> TraditionalForm in s.

