Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!cmcl2!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn )
Newsgroups: comp.unix.questions
Subject: Re: How to determine file being redirected to in C
Keywords: redirection
Message-ID: <9745@smoke.BRL.MIL>
Date: 28 Feb 89 04:28:28 GMT
References: <10@sherpa.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 17

In article <10@sherpa.UUCP> rac@sherpa.UUCP (Roger A. Cornelius) writes:
>... can someone tell me how to determine (in C)
>if output is being redirected, or more precisely, how to determine the
>file output is being redirected to.  The cat command does this (at
>least the Xenix version of cat, I don't think the BSD version does),

What "cat" actually does is compare the device/inode numbers
for equality; it cannot determine "the" filename because there
may not be one, or it may be ambiguous (and would be expensive
to figure out anyway).  The device/inode numbers are obtained
from the fstat() system call.  These days, the system ID should
also be compared.

To determine a filename, assuming you can, for the inode
behind a given file descriptor, is a tedious process.  Your
best bet is to find another solution to whatever your problem
is.