def _demo_posix():
#
# Example 1: Simple redirection: Get process list
#
plist = Popen(["ps"], stdout=PIPE).communicate()[0]
print "Process list:"
print plist
#
# Example 2: Change uid before executing child
#
if os.getuid() == 0:
p = Popen(["id"], preexec_fn=lambda: os.setuid(100))
p.wait()
#
# Example 3: Connecting several subprocesses
#
print "Looking for 'hda'..."
p1 = Popen(["dmesg"], stdout=PIPE)
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
print repr(p2.communicate()[0])
#
# Example 4: Catch execution error
#
print
print "Trying a weird file..."
try:
print Popen(["/this/path/does/not/exist"]).communicate()
except OSError, e:
if e.errno == errno.ENOENT:
print "The file didn't exist. I thought so..."
print "Child traceback:"
print e.child_traceback
else:
print "Error", e.errno
else:
print >>sys.stderr, "Gosh. No error."
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