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# This is a copy of the popen2.py module of Python 1.5.2.
# It has been modified to pass stdin as file descriptor 2 instead of 0.
# This means the child process initially uses the existing stdin. This is
# required for "su" to work on Linux, where it must be a tty.
# After passing "su" the executed command is expected to connect stdin to file
# descriptor 2.
#
# Some things that are not obvious:
# - There are two things:
# 1. file descriptors that Unix uses, an integer number
# 2. Python file objects
# - The returned file objects must be closed, otherwise a stale handle causes
# trouble for the next call. It's not clear why.
# - One descriptor is used for two directions. Closing it for one directions
# also closes it for the other direction. But there are two file objects for
# it that also must be closed. Need to catch and ignore an error when
# closing the second one.
# - On some systems a bidirectional pipe is not possible. stderr will then not
# be connected.
import os
import sys
MAXFD = 256 # Max number of file descriptors (os.getdtablesize()???)
_active = []
def _cleanup():
for inst in _active[:]:
inst.poll()
class Popen3:
def __init__(self, cmd, capturestderr=0, bufsize=-1):
n = capturestderr # using stderr is disabled, avoid a warning
if type(cmd) == type(''):
cmd = ['/bin/sh', '-c', cmd]
p2cread, p2cwrite = os.pipe()
c2pread, c2pwrite = os.pipe()
self.pid = os.fork()
if self.pid == 0:
# Child
os.close(2)
n = os.dup(p2cread)
if n <> 2:
sys.stderr.write('popen2: bad read dup: %d\n' % n)
os.close(1)
n = os.dup(c2pwrite)
if n <> 1:
sys.stderr.write('popen2: bad write dup: %d\n' % n)
for i in range(3, MAXFD):
try:
os.close(i)
except: pass
try:
os.execvp(cmd[0], cmd)
finally:
os._exit(1)
# Shouldn't come here, I guess
os._exit(1)
os.close(p2cread)
self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
os.close(c2pwrite)
self.fromchild = os.fdopen(c2pread, 'r', bufsize)
try:
self.childerr = os.fdopen(p2cwrite, 'r', bufsize)
except:
# On some systems sockets are not bidirectional
self.childerr = None
self.sts = -1 # Child not completed yet
_active.append(self)
def poll(self):
if self.sts < 0:
try:
pid, sts = os.waitpid(self.pid, os.WNOHANG)
if pid == self.pid:
self.sts = sts
_active.remove(self)
except os.error:
pass
return self.sts
def wait(self):
pid, sts = os.waitpid(self.pid, 0)
if pid == self.pid:
self.sts = sts
_active.remove(self)
return self.sts
def popen3(cmd, bufsize=-1):
_cleanup()
inst = Popen3(cmd, 1, bufsize)
return inst.fromchild, inst.tochild, inst.childerr
def _test():
teststr = "abc\n"
print "testing popen3: reading from stdout..."
r, w, e = popen3('cat <&2')
w.write(teststr)
w.close()
assert r.read() == teststr
r.close()
try:
e.close()
except:
pass
print "testing popen3: reading from stderr..."
r, w, e = popen3('cat /etc/group >&2')
assert e.read() == open("/etc/group").read()
w.close()
r.close()
try:
e.close()
except:
pass
print "testing popen3: reading an error message..."
r, w, e = popen3('cat -abcdefghi')
err = e.read()
print "Between the ----- lines should be an error message from 'cat':"
print "-----\n%s-----" % err
assert err != ''
w.close()
r.close()
try:
e.close()
except:
pass
_cleanup()
assert not _active
print "All OK"
if __name__ == '__main__':
_test()
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