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"""Spawn a command with pipes to its stdin, stdout, and optionally stderr.
The normal os.popen(cmd, mode) call spawns a shell command and provides a
file interface to just the input or output of the process depending on
whether mode is 'r' or 'w'. This module provides the functions popen2(cmd)
and popen3(cmd) which return two or three pipes to the spawned command.
"""
import os
import sys
import string
MAXFD = 256 # Max number of file descriptors (os.getdtablesize()???)
_active = []
def _cleanup():
for inst in _active[:]:
inst.poll()
class Popen3:
"""Class representing a child process. Normally instances are created
by the factory functions popen2() and popen3()."""
def __init__(self, cmd, capturestderr=0, bufsize=-1):
"""The parameter 'cmd' is the shell command to execute in a
sub-process. The 'capturestderr' flag, if true, specifies that
the object should capture standard error output of the child process.
The default is false. If the 'bufsize' parameter is specified, it
specifies the size of the I/O buffers to/from the child process."""
if type(cmd) == type(''):
cmd = ['/bin/sh', '-c', cmd]
p2cread, p2cwrite = os.pipe()
c2pread, c2pwrite = os.pipe()
if capturestderr:
errout, errin = os.pipe()
self.pid = os.fork()
if self.pid == 0:
# Child
os.close(0)
os.close(1)
if os.dup(p2cread) <> 0:
sys.stderr.write('popen2: bad read dup\n')
if os.dup(c2pwrite) <> 1:
sys.stderr.write('popen2: bad write dup\n')
if capturestderr:
os.close(2)
if os.dup(errin) <> 2: pass
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)
if capturestderr:
os.close(errin)
self.childerr = os.fdopen(errout, 'r', bufsize)
else:
self.childerr = None
self.sts = -1 # Child not completed yet
_active.append(self)
def poll(self):
"""Return the exit status of the child process if it has finished,
or -1 if it hasn't finished yet."""
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):
"""Wait for and return the exit status of the child process."""
pid, sts = os.waitpid(self.pid, 0)
if pid == self.pid:
self.sts = sts
_active.remove(self)
return self.sts
if sys.platform[:3] == "win":
def popen2(cmd, mode='t', bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. If 'bufsize' is
specified, it sets the buffer size for the I/O pipes. The file objects
(child_stdout, child_stdin) are returned."""
w, r = os.popen2(cmd, mode, bufsize)
return r, w
else:
def popen2(cmd, mode='t', bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. If 'bufsize' is
specified, it sets the buffer size for the I/O pipes. The file objects
(child_stdout, child_stdin) are returned."""
if type(mode) is type(0) and bufsize == -1:
bufsize = mode
mode = 't'
assert mode in ('t', 'b')
_cleanup()
inst = Popen3(cmd, 0, bufsize)
return inst.fromchild, inst.tochild
if sys.platform[:3] == "win":
def popen3(cmd, mode='t', bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. If 'bufsize' is
specified, it sets the buffer size for the I/O pipes. The file objects
(child_stdout, child_stdin, child_stderr) are returned."""
w, r, e = os.popen3(cmd, mode, bufsize)
return r, w, e
else:
def popen3(cmd, mode='t', bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. If 'bufsize' is
specified, it sets the buffer size for the I/O pipes. The file objects
(child_stdout, child_stdin, child_stderr) are returned."""
if type(mode) is type(0) and bufsize == -1:
bufsize = mode
mode = 't'
assert mode in ('t', 'b')
_cleanup()
inst = Popen3(cmd, 1, bufsize)
return inst.fromchild, inst.tochild, inst.childerr
if sys.platform[:3] == "win":
def popen4(cmd, mode='t', bufsize=-1):
"""Execute the shell command 'cmd' in a sub-process. If 'bufsize' is
specified, it sets the buffer size for the I/O pipes. The file objects
(child_stdout_stderr, child_stdin) are returned."""
w, r = os.popen4(cmd, mode, bufsize)
return r, w
else:
pass # not yet on unix
def _test():
cmd = "cat"
teststr = "ab cd\n"
if os.name == "nt":
cmd = "more"
# "more" doesn't act the same way across Windows flavors,
# sometimes adding an extra newline at the start or the
# end. So we strip whitespace off both ends for comparison.
expected = teststr.strip()
print "testing popen2..."
r, w = popen2(cmd)
w.write(teststr)
w.close()
got = r.read()
if got.strip() != expected:
raise ValueError("wrote %s read %s" % (`teststr`, `got`))
print "testing popen3..."
try:
r, w, e = popen3([cmd])
except:
r, w, e = popen3(cmd)
w.write(teststr)
w.close()
got = r.read()
if got.strip() != expected:
raise ValueError("wrote %s read %s" % (`teststr`, `got`))
got = e.read()
if got:
raise ValueError("unexected %s on stderr" % `got`)
for inst in _active[:]:
inst.wait()
if _active:
raise ValueError("_active not empty")
print "All OK"
if __name__ == '__main__':
_test()
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