🚀 go-pugleaf

In <1991Apr18.165820.6035@amc.com> jwbirdsa@amc.com (James Birdsall) writes:

>In article <1991Apr16.145847.20316@midway.uchicago.edu> valley@gsbsun.uchicago.edu (Doug Dougherty) writes:
>>collinsa@p4.cs.man.ac.uk (Adrian Collins) writes:
>>>Does anybody know how to sense whether output redirection has been used
>>>on the command line?
>>isatty(1)
>>(Works in Turbo C)

>   Well, almost. isatty() returns true if the supplied handle is the
>console *or* a printer or serial port. Determining whether the handle is
>actually the console or not requires an ioctl() and checking some bits.

This is what I actually wanted to do, although I didn't really make it
very clear in my original article.

As I've had quite a few requests for responses to my original query, here
is a method of working out whether STDIN and STDOUT are being redirected.
This is a slightly altered version of the code sent to me by
Nick FitzGerald. 

unsigned int get_device_data(int handle)
{
union REGS regs;

regs.h.ah = 0x44;           /*  function number  */
regs.h.al = 0;              /*  subfunction number  */
regs.x.bx = handle;         /*  file or device handle  */
int86(0x21,&regs,&regs);
return ( regs.x.dx );
}

int output_redirected()
{
return ( ( get_device_data(fileno(stdout)) & 0x82 ) != 0x82 );
}

int input_redirected()
{
return ( ( get_device_data(fileno(stdin)) & 0x81) != 0x81 );
}

The masks have been altered to 0x81 & 0x82 from 0x01 and 0x02, so that the
code correctly senses output redirected to a file.

Thanks to everybody for your help.

Cheers,
  Adrian
---
Adrian Collins                              collinsa@uk.ac.man.cs.p4
Department of Computer Science              a.m.collins@uk.ac.mcc
University of Manchester
Manchester,                                 "Let me face the peril"
UK.                                         "No, it's too perilous!"
                                                    - The Holy Grail