What is wrong with running unix processes with &?

hop of those help? This works on Mac OS X 10.5.5. Note the capital -U option. Perhaps that's been your problem.

import subprocess
ps = subprocess.Popen("ps -U 0", shell=True, stdout=subprocess.PIPE)
print ps.stdout.read()
ps.stdout.close()
ps.wait()

Python 2.5.2 (r252:60911, Feb 22 2008, 07:57:53) 
[GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin

This might help you From the discussion it turned out that you not really intended to redirect the output of already running processes to somewhere else. But you seem to be trying to modify the output of a process you are starting .
With bash (seems to be what you are using) you may use [FD]>TARGET resp. [FD]. (2 is the well-known file descriptor for stderr). TARGET or SOURCE my be file system objects (e.g. files, devices, named pipes, unix domain sockets) or &FD where FD again is a file descriptor number and indicates the (open) filedescriptor to use.

awk '{ print "'"$SOME_ENV_VAR"'|" $0;}'

awk -v var="$SOME_ENV_VAR" '{ print var "|" $0;}'

(((echo hallo; echo ERROR >&2) | awk '{ print "stdout|" $0; }' >&4) 2>&1|  awk '{ print "stderr: " $0;}' ) 4>&1