244 lines
9.4 KiB
Python
244 lines
9.4 KiB
Python
"""Spawn a command with pipes to its stdin, stdout, and optionally stderr.
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The normal os.popen(cmd, mode) call spawns a shell command and provides a
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file interface to just the input or output of the process depending on
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whether mode is 'r' or 'w'. This module provides the functions popen2(cmd)
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and popen3(cmd) which return two or three pipes to the spawned command.
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"""
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import os
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import sys
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__all__ = ["popen2", "popen3", "popen4"]
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try:
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MAXFD = os.sysconf('SC_OPEN_MAX')
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except (AttributeError, ValueError):
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MAXFD = 256
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_active = []
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def _cleanup():
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for inst in _active[:]:
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if inst.poll(_deadstate=sys.maxint) >= 0:
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try:
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_active.remove(inst)
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except ValueError:
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# This can happen if two threads create a new Popen instance.
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# It's harmless that it was already removed, so ignore.
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pass
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class Popen3:
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"""Class representing a child process. Normally instances are created
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by the factory functions popen2() and popen3()."""
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sts = -1 # Child not completed yet
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def __init__(self, cmd, capturestderr=False, bufsize=-1):
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"""The parameter 'cmd' is the shell command to execute in a
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sub-process. On UNIX, 'cmd' may be a sequence, in which case arguments
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will be passed directly to the program without shell intervention (as
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with os.spawnv()). If 'cmd' is a string it will be passed to the shell
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(as with os.system()). The 'capturestderr' flag, if true, specifies
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that the object should capture standard error output of the child
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process. The default is false. If the 'bufsize' parameter is
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specified, it specifies the size of the I/O buffers to/from the child
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process."""
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_cleanup()
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self.cmd = cmd
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p2cread, p2cwrite = os.pipe()
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c2pread, c2pwrite = os.pipe()
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if capturestderr:
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errout, errin = os.pipe()
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self.pid = os.fork()
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if self.pid == 0:
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# Child
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os.dup2(p2cread, 0)
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os.dup2(c2pwrite, 1)
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if capturestderr:
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os.dup2(errin, 2)
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self._run_child(cmd)
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os.close(p2cread)
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self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
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os.close(c2pwrite)
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self.fromchild = os.fdopen(c2pread, 'r', bufsize)
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if capturestderr:
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os.close(errin)
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self.childerr = os.fdopen(errout, 'r', bufsize)
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else:
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self.childerr = None
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def __del__(self):
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# In case the child hasn't been waited on, check if it's done.
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self.poll(_deadstate=sys.maxint)
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if self.sts < 0:
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if _active is not None:
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# Child is still running, keep us alive until we can wait on it.
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_active.append(self)
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def _run_child(self, cmd):
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if isinstance(cmd, basestring):
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cmd = ['/bin/sh', '-c', cmd]
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for i in xrange(3, MAXFD):
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try:
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os.close(i)
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except OSError:
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pass
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try:
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os.execvp(cmd[0], cmd)
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finally:
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os._exit(1)
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def poll(self, _deadstate=None):
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"""Return the exit status of the child process if it has finished,
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or -1 if it hasn't finished yet."""
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if self.sts < 0:
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try:
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pid, sts = os.waitpid(self.pid, os.WNOHANG)
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# pid will be 0 if self.pid hasn't terminated
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if pid == self.pid:
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self.sts = sts
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except os.error:
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if _deadstate is not None:
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self.sts = _deadstate
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return self.sts
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def wait(self):
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"""Wait for and return the exit status of the child process."""
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if self.sts < 0:
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pid, sts = os.waitpid(self.pid, 0)
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# This used to be a test, but it is believed to be
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# always true, so I changed it to an assertion - mvl
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assert pid == self.pid
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self.sts = sts
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return self.sts
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class Popen4(Popen3):
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childerr = None
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def __init__(self, cmd, bufsize=-1):
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_cleanup()
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self.cmd = cmd
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p2cread, p2cwrite = os.pipe()
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c2pread, c2pwrite = os.pipe()
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self.pid = os.fork()
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if self.pid == 0:
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# Child
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os.dup2(p2cread, 0)
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os.dup2(c2pwrite, 1)
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os.dup2(c2pwrite, 2)
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self._run_child(cmd)
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os.close(p2cread)
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self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
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os.close(c2pwrite)
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self.fromchild = os.fdopen(c2pread, 'r', bufsize)
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if sys.platform[:3] == "win" or sys.platform == "os2emx":
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# Some things don't make sense on non-Unix platforms.
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del Popen3, Popen4
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def popen2(cmd, bufsize=-1, mode='t'):
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"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
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be a sequence, in which case arguments will be passed directly to the
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program without shell intervention (as with os.spawnv()). If 'cmd' is a
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string it will be passed to the shell (as with os.system()). If
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'bufsize' is specified, it sets the buffer size for the I/O pipes. The
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file objects (child_stdout, child_stdin) are returned."""
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w, r = os.popen2(cmd, mode, bufsize)
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return r, w
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def popen3(cmd, bufsize=-1, mode='t'):
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"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
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be a sequence, in which case arguments will be passed directly to the
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program without shell intervention (as with os.spawnv()). If 'cmd' is a
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string it will be passed to the shell (as with os.system()). If
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'bufsize' is specified, it sets the buffer size for the I/O pipes. The
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file objects (child_stdout, child_stdin, child_stderr) are returned."""
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w, r, e = os.popen3(cmd, mode, bufsize)
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return r, w, e
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def popen4(cmd, bufsize=-1, mode='t'):
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"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
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be a sequence, in which case arguments will be passed directly to the
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program without shell intervention (as with os.spawnv()). If 'cmd' is a
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string it will be passed to the shell (as with os.system()). If
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'bufsize' is specified, it sets the buffer size for the I/O pipes. The
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file objects (child_stdout_stderr, child_stdin) are returned."""
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w, r = os.popen4(cmd, mode, bufsize)
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return r, w
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else:
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def popen2(cmd, bufsize=-1, mode='t'):
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"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
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be a sequence, in which case arguments will be passed directly to the
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program without shell intervention (as with os.spawnv()). If 'cmd' is a
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string it will be passed to the shell (as with os.system()). If
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'bufsize' is specified, it sets the buffer size for the I/O pipes. The
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file objects (child_stdout, child_stdin) are returned."""
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inst = Popen3(cmd, False, bufsize)
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return inst.fromchild, inst.tochild
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def popen3(cmd, bufsize=-1, mode='t'):
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"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
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be a sequence, in which case arguments will be passed directly to the
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program without shell intervention (as with os.spawnv()). If 'cmd' is a
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string it will be passed to the shell (as with os.system()). If
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'bufsize' is specified, it sets the buffer size for the I/O pipes. The
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file objects (child_stdout, child_stdin, child_stderr) are returned."""
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inst = Popen3(cmd, True, bufsize)
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return inst.fromchild, inst.tochild, inst.childerr
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def popen4(cmd, bufsize=-1, mode='t'):
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"""Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may
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be a sequence, in which case arguments will be passed directly to the
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program without shell intervention (as with os.spawnv()). If 'cmd' is a
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string it will be passed to the shell (as with os.system()). If
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'bufsize' is specified, it sets the buffer size for the I/O pipes. The
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file objects (child_stdout_stderr, child_stdin) are returned."""
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inst = Popen4(cmd, bufsize)
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return inst.fromchild, inst.tochild
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__all__.extend(["Popen3", "Popen4"])
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def _test():
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# When the test runs, there shouldn't be any open pipes
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_cleanup()
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assert not _active, "Active pipes when test starts " + repr([c.cmd for c in _active])
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cmd = "cat"
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teststr = "ab cd\n"
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if os.name == "nt":
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cmd = "more"
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# "more" doesn't act the same way across Windows flavors,
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# sometimes adding an extra newline at the start or the
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# end. So we strip whitespace off both ends for comparison.
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expected = teststr.strip()
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print "testing popen2..."
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r, w = popen2(cmd)
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w.write(teststr)
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w.close()
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got = r.read()
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if got.strip() != expected:
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raise ValueError("wrote %r read %r" % (teststr, got))
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print "testing popen3..."
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try:
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r, w, e = popen3([cmd])
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except:
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r, w, e = popen3(cmd)
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w.write(teststr)
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w.close()
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got = r.read()
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if got.strip() != expected:
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raise ValueError("wrote %r read %r" % (teststr, got))
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got = e.read()
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if got:
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raise ValueError("unexpected %r on stderr" % (got,))
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for inst in _active[:]:
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inst.wait()
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_cleanup()
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if _active:
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raise ValueError("_active not empty")
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print "All OK"
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if __name__ == '__main__':
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_test()
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