Can you fool isatty AND log stdout and stderr separately?

Like this?

% ./challenge.py >stdout 2>stderr% cat stdout This is a real tty :)standard output data% cat stderr standard error data

Because I cheated a little bit. ;-)

% echo $LD_PRELOAD/home/karol/preload.so

Like so...

% gcc preload.c -shared -o preload.so -fPIC

I feel dirty now, but it was fun. :D

% cat preload.c#include <stdlib.h>int isatty(int fd) {    if(fd == 2 || fd == 1) {        return 1;    }    return 0;}char* ttyname(int fd) {    static char* fake_name = "/dev/fake";    if(fd == 2 || fd == 1) {        return fake_name;    }    return NULL;}

For a simpler use-case (e.g. development testing), use strace (linux) or dtruss (OSX). Of course that won't work in privileged process.

Here's a sample, you can distinguish stdout fd1 from stderr fd2:

$ strace -ewrite python2 test.py[snip]write(1, "This is a real tty :)\n", 22This is a real tty :)) = 22write(2, "standard error data", 19standard error data)     = 19write(1, "standard output data", 20standard output data)    = 20+++ exited with 0 +++

In the sample above you see each standard xxx data doubled, because you can't redirect stdout/stderr. You can, however ask strace to save its output to a file.

On a theoretical side, if stdout and stderr refer to the same terminal, you can only distinguish between the 2 while still in the context of your process, either in user mode (LD_PRELOAD), or kernel space (ptrace interface that strace tool uses). Once the data hits actual device, real of pseudo, the distinction is lost.

You can always allocate Pseudo-TTY, that's what screen does.

In Python you'd access it using pty.openpty()

This "master" code passes your test:

import subprocess, pty, osm, s = pty.openpty()fm = os.fdopen(m, "rw")p = subprocess.Popen(["python2", "test.py"], stdin=s, stdout=s, stderr=s)p.communicate()os.close(s)print fm.read()

Of course if you want to distinguish between stdin/out/err, your "slave" process will see different PYT names:

inp = pty.openpty()oup = pty.openpty()erp = pty.openpty()subprocess.Popen([command, args], stdin=inp[1], stdout=uop[1], stderr=erp[1])