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
  93 if sys.platform[:3] == "win":
  94     def popen2(cmd, mode='t', bufsize=-1):
  95         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
  96         specified, it sets the buffer size for the I/O pipes.  The file objects
  97         (child_stdout, child_stdin) are returned."""
  98         w, r = os.popen2(cmd, mode, bufsize)
  99         return r, w
 100 else:
 101     def popen2(cmd, mode='t', bufsize=-1):
 102         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 103         specified, it sets the buffer size for the I/O pipes.  The file objects
 104         (child_stdout, child_stdin) are returned."""
 105         if type(mode) is type(0) and bufsize == -1:
 106             bufsize = mode
 107             mode = 't'
 108         assert mode in ('t', 'b')
 109         _cleanup()
 110         inst = Popen3(cmd, 0, bufsize)
 111         return inst.fromchild, inst.tochild
 112
 113 if sys.platform[:3] == "win":
 114     def popen3(cmd, mode='t', bufsize=-1):
 115         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 116         specified, it sets the buffer size for the I/O pipes.  The file objects
 117         (child_stdout, child_stdin, child_stderr) are returned."""
 118         w, r, e = os.popen3(cmd, mode, bufsize)
 119         return r, w, e
 120 else:
 121     def popen3(cmd, mode='t', bufsize=-1):
 122         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 123         specified, it sets the buffer size for the I/O pipes.  The file objects
 124         (child_stdout, child_stdin, child_stderr) are returned."""
 125         if type(mode) is type(0) and bufsize == -1:
 126             bufsize = mode
 127             mode = 't'
 128         assert mode in ('t', 'b')
 129         _cleanup()
 130         inst = Popen3(cmd, 1, bufsize)
 131         return inst.fromchild, inst.tochild, inst.childerr
 132
 133 if sys.platform[:3] == "win":
 134     def popen4(cmd, mode='t', bufsize=-1):
 135         """Execute the shell command 'cmd' in a sub-process.  If 'bufsize' is
 136         specified, it sets the buffer size for the I/O pipes.  The file objects
 137         (child_stdout_stderr, child_stdin) are returned."""
 138         w, r = os.popen4(cmd, mode, bufsize)
 139         return r, w
 140 else:
 141     pass # not yet on unix
 142
 143
 144 def _test():
 145     cmd  = "cat"
 146     teststr = "ab cd\n"
 147     if os.name == "nt":
 148         cmd = "more"
 149     # "more" doesn't act the same way across Windows flavors,
 150     # sometimes adding an extra newline at the start or the
 151     # end.  So we strip whitespace off both ends for comparison.
 152     expected = teststr.strip()
 153     print "testing popen2..."
 154     r, w = popen2(cmd)
 155     w.write(teststr)
 156     w.close()
 157     got = r.read()
 158     if got.strip() != expected:
 159         raise ValueError("wrote %s read %s" % (`teststr`, `got`))
 160     print "testing popen3..."
 161     try:
 162         r, w, e = popen3([cmd])
 163     except:
 164         r, w, e = popen3(cmd)
 165     w.write(teststr)
 166     w.close()
 167     got = r.read()
 168     if got.strip() != expected:
 169         raise ValueError("wrote %s read %s" % (`teststr`, `got`))
 170     got = e.read()
 171     if got:
 172         raise ValueError("unexected %s on stderr" % `got`)
 173     for inst in _active[:]:
 174         inst.wait()
 175     if _active:
 176         raise ValueError("_active not empty")
 177     print "All OK"
 178
 179 if __name__ == '__main__':
 180     _test()