Lib/popen2.py

   1 """Spawn a command with pipes to its stdin, stdout, and optionally stderr.
   2
   3 The normal os.popen(cmd, mode) call spawns a shell command and provides a
   4 file interface to just the input or output of the process depending on
   5 whether mode is 'r' or 'w'.  This module provides the functions popen2(cmd)
   6 and popen3(cmd) which return two or three pipes to the spawned command.
   7 """
   8
   9 import os
  10 import sys
  11 import types
  12
  13 __all__ = ["popen2", "popen3", "popen4"]
  14
  15 MAXFD = 256     # Max number of file descriptors (os.getdtablesize()???)
  16
  17 _active = []
  18
  19 def _cleanup():
  20     for inst in _active[:]:
  21         inst.poll()
  22
  23 class Popen3:
  24     """Class representing a child process.  Normally instances are created
  25     by the factory functions popen2() and popen3()."""
  26
  27     sts = -1                    # Child not completed yet
  28
  29     def __init__(self, cmd, capturestderr=0, bufsize=-1):
  30         """The parameter 'cmd' is the shell command to execute in a
  31         sub-process.  The 'capturestderr' flag, if true, specifies that
  32         the object should capture standard error output of the child process.
  33         The default is false.  If the 'bufsize' parameter is specified, it
  34         specifies the size of the I/O buffers to/from the child process."""
  35         _cleanup()
  36         p2cread, p2cwrite = os.pipe()
  37         c2pread, c2pwrite = os.pipe()
  38         if capturestderr:
  39             errout, errin = os.pipe()
  40         self.pid = os.fork()
  41         if self.pid == 0:
  42             # Child
  43             os.dup2(p2cread, 0)
  44             os.dup2(c2pwrite, 1)
  45             if capturestderr:
  46                 os.dup2(errin, 2)
  47             self._run_child(cmd)
  48         os.close(p2cread)
  49         self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
  50         os.close(c2pwrite)
  51         self.fromchild = os.fdopen(c2pread, 'r', bufsize)
  52         if capturestderr:
  53             os.close(errin)
  54             self.childerr = os.fdopen(errout, 'r', bufsize)
  55         else:
  56             self.childerr = None
  57         _active.append(self)
  58
  59     def _run_child(self, cmd):
  60         if isinstance(cmd, types.StringTypes):
  61             cmd = ['/bin/sh', '-c', cmd]
  62         for i in range(3, MAXFD):
  63             try:
  64                 os.close(i)
  65             except:
  66                 pass
  67         try:
  68             os.execvp(cmd[0], cmd)
  69         finally:
  70             os._exit(1)
  71
  72     def poll(self):
  73         """Return the exit status of the child process if it has finished,
  74         or -1 if it hasn't finished yet."""
  75         if self.sts < 0:
  76             try:
  77                 pid, sts = os.waitpid(self.pid, os.WNOHANG)
  78                 if pid == self.pid:
  79                     self.sts = sts
  80                     _active.remove(self)
  81             except os.error:
  82                 pass
  83         return self.sts
  84
  85     def wait(self):
  86         """Wait for and return the exit status of the child process."""
  87         pid, sts = os.waitpid(self.pid, 0)
  88         if pid == self.pid:
  89             self.sts = sts
  90             _active.remove(self)
  91         return self.sts
  92
  93
  94 class Popen4(Popen3):
  95     childerr = None
  96
  97     def __init__(self, cmd, bufsize=-1):
  98         _cleanup()
  99         p2cread, p2cwrite = os.pipe()
 100         c2pread, c2pwrite = os.pipe()
 101         self.pid = os.fork()
 102         if self.pid == 0:
 103             # Child
 104             os.dup2(p2cread, 0)
 105             os.dup2(c2pwrite, 1)
 106             os.dup2(c2pwrite, 2)
 107             self._run_child(cmd)
 108         os.close(p2cread)
 109         self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
 110         os.close(c2pwrite)
 111         self.fromchild = os.fdopen(c2pread, 'r', bufsize)
 112         _active.append(self)
 113
 114
 115 if sys.platform[:3] == "win":
 116     # Some things don't make sense on non-Unix platforms.
 117     del Popen3, Popen4
 118
 119     def popen2(cmd, bufsize=-1, mode='t'):
 120         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 121         specified, it sets the buffer size for the I/O pipes.  The file objects
 122         (child_stdout, child_stdin) are returned."""
 123         w, r = os.popen2(cmd, mode, bufsize)
 124         return r, w
 125
 126     def popen3(cmd, bufsize=-1, mode='t'):
 127         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 128         specified, it sets the buffer size for the I/O pipes.  The file objects
 129         (child_stdout, child_stdin, child_stderr) are returned."""
 130         w, r, e = os.popen3(cmd, mode, bufsize)
 131         return r, w, e
 132
 133     def popen4(cmd, bufsize=-1, mode='t'):
 134         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 135         specified, it sets the buffer size for the I/O pipes.  The file objects
 136         (child_stdout_stderr, child_stdin) are returned."""
 137         w, r = os.popen4(cmd, mode, bufsize)
 138         return r, w
 139 else:
 140     def popen2(cmd, bufsize=-1, mode='t'):
 141         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 142         specified, it sets the buffer size for the I/O pipes.  The file objects
 143         (child_stdout, child_stdin) are returned."""
 144         inst = Popen3(cmd, 0, bufsize)
 145         return inst.fromchild, inst.tochild
 146
 147     def popen3(cmd, bufsize=-1, mode='t'):
 148         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 149         specified, it sets the buffer size for the I/O pipes.  The file objects
 150         (child_stdout, child_stdin, child_stderr) are returned."""
 151         inst = Popen3(cmd, 1, bufsize)
 152         return inst.fromchild, inst.tochild, inst.childerr
 153
 154     def popen4(cmd, bufsize=-1, mode='t'):
 155         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 156         specified, it sets the buffer size for the I/O pipes.  The file objects
 157         (child_stdout_stderr, child_stdin) are returned."""
 158         inst = Popen4(cmd, bufsize)
 159         return inst.fromchild, inst.tochild
 160
 161     __all__.extend(["Popen3", "Popen4"])
 162
 163 def _test():
 164     cmd  = "cat"
 165     teststr = "ab cd\n"
 166     if os.name == "nt":
 167         cmd = "more"
 168     # "more" doesn't act the same way across Windows flavors,
 169     # sometimes adding an extra newline at the start or the
 170     # end.  So we strip whitespace off both ends for comparison.
 171     expected = teststr.strip()
 172     print "testing popen2..."
 173     r, w = popen2(cmd)
 174     w.write(teststr)
 175     w.close()
 176     got = r.read()
 177     if got.strip() != expected:
 178         raise ValueError("wrote %s read %s" % (`teststr`, `got`))
 179     print "testing popen3..."
 180     try:
 181         r, w, e = popen3([cmd])
 182     except:
 183         r, w, e = popen3(cmd)
 184     w.write(teststr)
 185     w.close()
 186     got = r.read()
 187     if got.strip() != expected:
 188         raise ValueError("wrote %s read %s" % (`teststr`, `got`))
 189     got = e.read()
 190     if got:
 191         raise ValueError("unexected %s on stderr" % `got`)
 192     for inst in _active[:]:
 193         inst.wait()
 194     if _active:
 195         raise ValueError("_active not empty")
 196     print "All OK"
 197
 198 if __name__ == '__main__':
 199     _test()