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 string
  12
  13 MAXFD = 256     # Max number of file descriptors (os.getdtablesize()???)
  14
  15 _active = []
  16
  17 def _cleanup():
  18     for inst in _active[:]:
  19         inst.poll()
  20
  21 class Popen3:
  22     """Class representing a child process.  Normally instances are created
  23     by the factory functions popen2() and popen3()."""
  24
  25     def __init__(self, cmd, capturestderr=0, bufsize=-1):
  26         """The parameter 'cmd' is the shell command to execute in a
  27         sub-process.  The 'capturestderr' flag, if true, specifies that
  28         the object should capture standard error output of the child process.
  29         The default is false.  If the 'bufsize' parameter is specified, it
  30         specifies the size of the I/O buffers to/from the child process."""
  31         if type(cmd) == type(''):
  32             cmd = ['/bin/sh', '-c', cmd]
  33         p2cread, p2cwrite = os.pipe()
  34         c2pread, c2pwrite = os.pipe()
  35         if capturestderr:
  36             errout, errin = os.pipe()
  37         self.pid = os.fork()
  38         if self.pid == 0:
  39             # Child
  40             os.close(0)
  41             os.close(1)
  42             if os.dup(p2cread) <> 0:
  43                 sys.stderr.write('popen2: bad read dup\n')
  44             if os.dup(c2pwrite) <> 1:
  45                 sys.stderr.write('popen2: bad write dup\n')
  46             if capturestderr:
  47                 os.close(2)
  48                 if os.dup(errin) <> 2: pass
  49             for i in range(3, MAXFD):
  50                 try:
  51                     os.close(i)
  52                 except: pass
  53             try:
  54                 os.execvp(cmd[0], cmd)
  55             finally:
  56                 os._exit(1)
  57             # Shouldn't come here, I guess
  58             os._exit(1)
  59         os.close(p2cread)
  60         self.tochild = os.fdopen(p2cwrite, 'w', bufsize)
  61         os.close(c2pwrite)
  62         self.fromchild = os.fdopen(c2pread, 'r', bufsize)
  63         if capturestderr:
  64             os.close(errin)
  65             self.childerr = os.fdopen(errout, 'r', bufsize)
  66         else:
  67             self.childerr = None
  68         self.sts = -1 # Child not completed yet
  69         _active.append(self)
  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 def popen2(cmd, bufsize=-1):
  93     """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
  94     specified, it sets the buffer size for the I/O pipes.  The file objects
  95     (child_stdout, child_stdin) are returned."""
  96     _cleanup()
  97     inst = Popen3(cmd, 0, bufsize)
  98     return inst.fromchild, inst.tochild
  99
 100 def popen3(cmd, bufsize=-1):
 101     """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 102     specified, it sets the buffer size for the I/O pipes.  The file objects
 103     (child_stdout, child_stdin, child_stderr) are returned."""
 104     _cleanup()
 105     inst = Popen3(cmd, 1, bufsize)
 106     return inst.fromchild, inst.tochild, inst.childerr
 107
 108 def _test():
 109     teststr = "abc\n"
 110     print "testing popen2..."
 111     r, w = popen2('cat')
 112     w.write(teststr)
 113     w.close()
 114     assert r.read() == teststr
 115     print "testing popen3..."
 116     r, w, e = popen3(['cat'])
 117     w.write(teststr)
 118     w.close()
 119     assert r.read() == teststr
 120     assert e.read() == ""
 121     for inst in _active[:]:
 122         inst.wait()
 123     assert not _active
 124     print "All OK"
 125
 126 if __name__ == '__main__':
 127     _test()