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
  12 __all__ = ["popen2", "popen3", "popen4"]
  13
  14 MAXFD = 256     # Max number of file descriptors (os.getdtablesize()???)
  15
  16 _active = []
  17
  18 def _cleanup():
  19     for inst in _active[:]:
  20         inst.poll()
  21
  22 class Popen3:
  23     """Class representing a child process.  Normally instances are created
  24     by the factory functions popen2() and popen3()."""
  25
  26     sts = -1                    # Child not completed yet
  27
  28     def __init__(self, cmd, capturestderr=0, bufsize=-1):
  29         """The parameter 'cmd' is the shell command to execute in a
  30         sub-process.  The 'capturestderr' flag, if true, specifies that
  31         the object should capture standard error output of the child process.
  32         The default is false.  If the 'bufsize' parameter is specified, it
  33         specifies the size of the I/O buffers to/from the child process."""
  34         _cleanup()
  35         p2cread, p2cwrite = os.pipe()
  36         c2pread, c2pwrite = os.pipe()
  37         if capturestderr:
  38             errout, errin = os.pipe()
  39         self.pid = os.fork()
  40         if self.pid == 0:
  41             # Child
  42             os.dup2(p2cread, 0)
  43             os.dup2(c2pwrite, 1)
  44             if capturestderr:
  45                 os.dup2(errin, 2)
  46             self._run_child(cmd)
  47         os.close(p2cread)
  48         self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
  49         os.close(c2pwrite)
  50         self.fromchild = os.fdopen(c2pread, 'r', bufsize)
  51         if capturestderr:
  52             os.close(errin)
  53             self.childerr = os.fdopen(errout, 'r', bufsize)
  54         else:
  55             self.childerr = None
  56         _active.append(self)
  57
  58     def _run_child(self, cmd):
  59         if isinstance(cmd, basestring):
  60             cmd = ['/bin/sh', '-c', cmd]
  61         for i in range(3, MAXFD):
  62             try:
  63                 os.close(i)
  64             except OSError:
  65                 pass
  66         try:
  67             os.execvp(cmd[0], cmd)
  68         finally:
  69             os._exit(1)
  70
  71     def poll(self):
  72         """Return the exit status of the child process if it has finished,
  73         or -1 if it hasn't finished yet."""
  74         if self.sts < 0:
  75             try:
  76                 pid, sts = os.waitpid(self.pid, os.WNOHANG)
  77                 if pid == self.pid:
  78                     self.sts = sts
  79                     _active.remove(self)
  80             except os.error:
  81                 pass
  82         return self.sts
  83
  84     def wait(self):
  85         """Wait for and return the exit status of the child process."""
  86         pid, sts = os.waitpid(self.pid, 0)
  87         if pid == self.pid:
  88             self.sts = sts
  89             _active.remove(self)
  90         return self.sts
  91
  92
  93 class Popen4(Popen3):
  94     childerr = None
  95
  96     def __init__(self, cmd, bufsize=-1):
  97         _cleanup()
  98         p2cread, p2cwrite = os.pipe()
  99         c2pread, c2pwrite = os.pipe()
 100         self.pid = os.fork()
 101         if self.pid == 0:
 102             # Child
 103             os.dup2(p2cread, 0)
 104             os.dup2(c2pwrite, 1)
 105             os.dup2(c2pwrite, 2)
 106             self._run_child(cmd)
 107         os.close(p2cread)
 108         self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
 109         os.close(c2pwrite)
 110         self.fromchild = os.fdopen(c2pread, 'r', bufsize)
 111         _active.append(self)
 112
 113
 114 if sys.platform[:3] == "win" or sys.platform == "os2emx":
 115     # Some things don't make sense on non-Unix platforms.
 116     del Popen3, Popen4
 117
 118     def popen2(cmd, bufsize=-1, mode='t'):
 119         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 120         specified, it sets the buffer size for the I/O pipes.  The file objects
 121         (child_stdout, child_stdin) are returned."""
 122         w, r = os.popen2(cmd, mode, bufsize)
 123         return r, w
 124
 125     def popen3(cmd, bufsize=-1, mode='t'):
 126         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 127         specified, it sets the buffer size for the I/O pipes.  The file objects
 128         (child_stdout, child_stdin, child_stderr) are returned."""
 129         w, r, e = os.popen3(cmd, mode, bufsize)
 130         return r, w, e
 131
 132     def popen4(cmd, bufsize=-1, mode='t'):
 133         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 134         specified, it sets the buffer size for the I/O pipes.  The file objects
 135         (child_stdout_stderr, child_stdin) are returned."""
 136         w, r = os.popen4(cmd, mode, bufsize)
 137         return r, w
 138 else:
 139     def popen2(cmd, bufsize=-1, mode='t'):
 140         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 141         specified, it sets the buffer size for the I/O pipes.  The file objects
 142         (child_stdout, child_stdin) are returned."""
 143         inst = Popen3(cmd, 0, bufsize)
 144         return inst.fromchild, inst.tochild
 145
 146     def popen3(cmd, bufsize=-1, mode='t'):
 147         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 148         specified, it sets the buffer size for the I/O pipes.  The file objects
 149         (child_stdout, child_stdin, child_stderr) are returned."""
 150         inst = Popen3(cmd, 1, bufsize)
 151         return inst.fromchild, inst.tochild, inst.childerr
 152
 153     def popen4(cmd, bufsize=-1, mode='t'):
 154         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 155         specified, it sets the buffer size for the I/O pipes.  The file objects
 156         (child_stdout_stderr, child_stdin) are returned."""
 157         inst = Popen4(cmd, bufsize)
 158         return inst.fromchild, inst.tochild
 159
 160     __all__.extend(["Popen3", "Popen4"])
 161
 162 def _test():
 163     cmd  = "cat"
 164     teststr = "ab cd\n"
 165     if os.name == "nt":
 166         cmd = "more"
 167     # "more" doesn't act the same way across Windows flavors,
 168     # sometimes adding an extra newline at the start or the
 169     # end.  So we strip whitespace off both ends for comparison.
 170     expected = teststr.strip()
 171     print "testing popen2..."
 172     r, w = popen2(cmd)
 173     w.write(teststr)
 174     w.close()
 175     got = r.read()
 176     if got.strip() != expected:
 177         raise ValueError("wrote %s read %s" % (`teststr`, `got`))
 178     print "testing popen3..."
 179     try:
 180         r, w, e = popen3([cmd])
 181     except:
 182         r, w, e = popen3(cmd)
 183     w.write(teststr)
 184     w.close()
 185     got = r.read()
 186     if got.strip() != expected:
 187         raise ValueError("wrote %s read %s" % (`teststr`, `got`))
 188     got = e.read()
 189     if got:
 190         raise ValueError("unexected %s on stderr" % `got`)
 191     for inst in _active[:]:
 192         inst.wait()
 193     if _active:
 194         raise ValueError("_active not empty")
 195     print "All OK"
 196
 197 if __name__ == '__main__':
 198     _test()