OpenEuphoria

Re: Redirection of output

• Posted by Juergen Luethje <jluethje at gmx.de> Jul 06, 2002
• 422 views

Hi all, I wrote:

> Hello Pete,

> you wrote:

>> On Mon, 1 Jul 2002 07:26:20 +0200, Juergen Luethje <jluethje at gmx.de>
>> wrote:

>>> how can a windows program detect, whether it's output has been
>>> redirected to a file?

>> I had a quick search for you and found this:
[decisive reference to int #21, ax=#4400]

> Thank you!!
> That looks like the DOS-Version of the function I'm looking for,
> but unfortunately I'm not able, to translate it to proper working
> Eu code. 
<snip>

After having one more look at Ralph Brown's interrupt list,
now I managed to write an appropriate Eu function.
(Maybe I could not imagine, that it is that simple. 

--------------------------------------------------------------->8---
redir.ex
--------------------------------------------------------------------
include machine.e

constant REG_LIST_SIZE = 10, CF = 1

global function output_redirected ()
   -- returns TRUE or FALSE, or -1 on error
   -- (after Ralf Brown's Interrupt List, Release 61 (2000))
   sequence reg_list

   reg_list = repeat(0, REG_LIST_SIZE)
   reg_list[REG_AX] = #4400
   reg_list[REG_BX] = 1   -- handle (1 = StdOut)
   reg_list[REG_FLAGS] = or_bits(reg_list[REG_FLAGS], 1)
   reg_list = dos_interrupt(#21, reg_list)
   if and_bits(reg_list[REG_FLAGS], CF) = 1 then
      return -1   -- error
   else
      return (and_bits(reg_list[REG_DX], #8000)  = 0)  -- redirected to a file
          or (and_bits(reg_list[REG_DX], #0004) != 0)  -- redirected to NUL
   end if
end function


-- Demo
integer ofn

puts(1, "Hello World!\n")
ofn = open("redir.log", "w")
printf(ofn, "redirected: %d", output_redirected())
close(ofn)
--------------------------------------------------------------->8---


To see what the program does, call it the following ways:
   ex.exe redir.ex
   ex.exe redir.ex > re.txt
   ex.exe redir.ex > nul

and after each call, read the text in redir.log.

Thanks again Pete, and best regards,
   Juergen


PS: Does anyone know how this could be done on Windows?