# subprocess - Subprocesses with accessible I/O streams

#

# For more information about this module, see PEP 324.

#

# This module should remain compatible with Python 2.2, see PEP 291.

#

# Copyright (c) 2003-2005 by Peter Astrand <astrand@lysator.liu.se>

#

# Licensed to PSF under a Contributor Agreement.

# See http://www.python.org/2.4/license for licensing details.

r"""subprocess - Subprocesses with accessible I/O streams

This module allows you to spawn processes, connect to their

input/output/error pipes, and obtain their return codes. This module

intends to replace several other, older modules and functions, like:

os.system

os.spawn*

os.popen*

popen2.*

commands.*

Information about how the subprocess module can be used to replace these

modules and functions can be found below.

Using the subprocess module

===========================

This module defines one class called Popen:

class Popen(args, bufsize=0, executable=None,

stdin=None, stdout=None, stderr=None,

preexec_fn=None, close_fds=False, shell=False,

cwd=None, env=None, universal_newlines=False,

startupinfo=None, creationflags=0):

Arguments are:

args should be a string, or a sequence of program arguments. The

program to execute is normally the first item in the args sequence or

string, but can be explicitly set by using the executable argument.

On UNIX, with shell=False (default): In this case, the Popen class

uses os.execvp() to execute the child program. args should normally

be a sequence. A string will be treated as a sequence with the string

as the only item (the program to execute).

On UNIX, with shell=True: If args is a string, it specifies the

command string to execute through the shell. If args is a sequence,

the first item specifies the command string, and any additional items

will be treated as additional shell arguments.

On Windows: the Popen class uses CreateProcess() to execute the child

program, which operates on strings. If args is a sequence, it will be

converted to a string using the list2cmdline method. Please note that

not all MS Windows applications interpret the command line the same

way: The list2cmdline is designed for applications using the same

rules as the MS C runtime.

bufsize, if given, has the same meaning as the corresponding argument

to the built-in open() function: 0 means unbuffered, 1 means line

buffered, any other positive value means use a buffer of

(approximately) that size. A negative bufsize means to use the system

default, which usually means fully buffered. The default value for

bufsize is 0 (unbuffered).

stdin, stdout and stderr specify the executed programs' standard

input, standard output and standard error file handles, respectively.

Valid values are PIPE, an existing file descriptor (a positive

integer), an existing file object, and None. PIPE indicates that a

new pipe to the child should be created. With None, no redirection

will occur; the child's file handles will be inherited from the

parent. Additionally, stderr can be STDOUT, which indicates that the

stderr data from the applications should be captured into the same

file handle as for stdout.

If preexec_fn is set to a callable object, this object will be called

in the child process just before the child is executed.

If close_fds is true, all file descriptors except 0, 1 and 2 will be

closed before the child process is executed.

if shell is true, the specified command will be executed through the

shell.

If cwd is not None, the current directory will be changed to cwd

before the child is executed.

If env is not None, it defines the environment variables for the new

process.

If universal_newlines is true, the file objects stdout and stderr are

opened as a text files, but lines may be terminated by any of '\n',

the Unix end-of-line convention, '\r', the Macintosh convention or

'\r\n', the Windows convention. All of these external representations

are seen as '\n' by the Python program. Note: This feature is only

available if Python is built with universal newline support (the

default). Also, the newlines attribute of the file objects stdout,

stdin and stderr are not updated by the communicate() method.

The startupinfo and creationflags, if given, will be passed to the

underlying CreateProcess() function. They can specify things such as

appearance of the main window and priority for the new process.

(Windows only)

This module also defines some shortcut functions:

call(*popenargs, **kwargs):

Run command with arguments. Wait for command to complete, then

return the returncode attribute.

The arguments are the same as for the Popen constructor. Example:

retcode = call(["ls", "-l"])

check_call(*popenargs, **kwargs):

Run command with arguments. Wait for command to complete. If the

exit code was zero then return, otherwise raise

CalledProcessError. The CalledProcessError object will have the

return code in the returncode attribute.

The arguments are the same as for the Popen constructor. Example:

check_call(["ls", "-l"])

check_output(*popenargs, **kwargs):

Run command with arguments and return its output as a byte string.

If the exit code was non-zero it raises a CalledProcessError. The

CalledProcessError object will have the return code in the returncode

attribute and output in the output attribute.

The arguments are the same as for the Popen constructor. Example:

output = check_output(["ls", "-l", "/dev/null"])

Exceptions

----------

Exceptions raised in the child process, before the new program has

started to execute, will be re-raised in the parent. Additionally,

the exception object will have one extra attribute called

'child_traceback', which is a string containing traceback information

from the childs point of view.

The most common exception raised is OSError. This occurs, for

example, when trying to execute a non-existent file. Applications

should prepare for OSErrors.

A ValueError will be raised if Popen is called with invalid arguments.

check_call() and check_output() will raise CalledProcessError, if the

called process returns a non-zero return code.

Security

--------

Unlike some other popen functions, this implementation will never call

/bin/sh implicitly. This means that all characters, including shell

metacharacters, can safely be passed to child processes.

Popen objects

=============

Instances of the Popen class have the following methods:

poll()

Check if child process has terminated. Returns returncode

attribute.

wait()

Wait for child process to terminate. Returns returncode attribute.

communicate(input=None)

Interact with process: Send data to stdin. Read data from stdout

and stderr, until end-of-file is reached. Wait for process to

terminate. The optional input argument should be a string to be

sent to the child process, or None, if no data should be sent to

the child.

communicate() returns a tuple (stdout, stderr).

Note: The data read is buffered in memory, so do not use this

method if the data size is large or unlimited.

The following attributes are also available:

stdin

If the stdin argument is PIPE, this attribute is a file object

that provides input to the child process. Otherwise, it is None.

stdout

If the stdout argument is PIPE, this attribute is a file object

that provides output from the child process. Otherwise, it is

None.

stderr

If the stderr argument is PIPE, this attribute is file object that

provides error output from the child process. Otherwise, it is

None.

pid

The process ID of the child process.

returncode

The child return code. A None value indicates that the process

hasn't terminated yet. A negative value -N indicates that the

child was terminated by signal N (UNIX only).

Replacing older functions with the subprocess module

====================================================

In this section, "a ==> b" means that b can be used as a replacement

for a.

Note: All functions in this section fail (more or less) silently if

the executed program cannot be found; this module raises an OSError

exception.

In the following examples, we assume that the subprocess module is

imported with "from subprocess import *".

Replacing /bin/sh shell backquote

---------------------------------

output=`mycmd myarg`

==>

output = Popen(["mycmd", "myarg"], stdout=PIPE).communicate()[0]

Replacing shell pipe line

-------------------------

output=`dmesg | grep hda`

==>

p1 = Popen(["dmesg"], stdout=PIPE)

p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)

output = p2.communicate()[0]

Replacing os.system()

---------------------

sts = os.system("mycmd" + " myarg")

==>

p = Popen("mycmd" + " myarg", shell=True)

pid, sts = os.waitpid(p.pid, 0)

Note:

* Calling the program through the shell is usually not required.

* It's easier to look at the returncode attribute than the

exitstatus.

A more real-world example would look like this:

try:

retcode = call("mycmd" + " myarg", shell=True)

if retcode < 0:

print >>sys.stderr, "Child was terminated by signal", -retcode

else:

print >>sys.stderr, "Child returned", retcode

except OSError, e:

print >>sys.stderr, "Execution failed:", e

Replacing os.spawn*

-------------------

P_NOWAIT example:

pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg")

==>

pid = Popen(["/bin/mycmd", "myarg"]).pid

P_WAIT example:

retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg")

==>

retcode = call(["/bin/mycmd", "myarg"])

Vector example:

os.spawnvp(os.P_NOWAIT, path, args)

==>

Popen([path] + args[1:])

Environment example:

os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env)

==>

Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"})

Replacing os.popen*

-------------------

pipe = os.popen("cmd", mode='r', bufsize)

==>

pipe = Popen("cmd", shell=True, bufsize=bufsize, stdout=PIPE).stdout

pipe = os.popen("cmd", mode='w', bufsize)

==>

pipe = Popen("cmd", shell=True, bufsize=bufsize, stdin=PIPE).stdin

(child_stdin, child_stdout) = os.popen2("cmd", mode, bufsize)

==>

p = Popen("cmd", shell=True, bufsize=bufsize,

stdin=PIPE, stdout=PIPE, close_fds=True)

(child_stdin, child_stdout) = (p.stdin, p.stdout)

(child_stdin,

child_stdout,

child_stderr) = os.popen3("cmd", mode, bufsize)

==>

p = Popen("cmd", shell=True, bufsize=bufsize,

stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)

(child_stdin,

child_stdout,

child_stderr) = (p.stdin, p.stdout, p.stderr)

(child_stdin, child_stdout_and_stderr) = os.popen4("cmd", mode,

bufsize)

==>

p = Popen("cmd", shell=True, bufsize=bufsize,

stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)

(child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout)

On Unix, os.popen2, os.popen3 and os.popen4 also accept a sequence as

the command to execute, in which case arguments will be passed

directly to the program without shell intervention. This usage can be

replaced as follows:

(child_stdin, child_stdout) = os.popen2(["/bin/ls", "-l"], mode,

bufsize)

==>

p = Popen(["/bin/ls", "-l"], bufsize=bufsize, stdin=PIPE, stdout=PIPE)

(child_stdin, child_stdout) = (p.stdin, p.stdout)

Return code handling translates as follows:

pipe = os.popen("cmd", 'w')

...

rc = pipe.close()

if rc is not None and rc % 256:

print "There were some errors"

==>

process = Popen("cmd", 'w', shell=True, stdin=PIPE)

...

process.stdin.close()

if process.wait() != 0:

print "There were some errors"

Replacing popen2.*

------------------

(child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode)

==>

p = Popen(["somestring"], shell=True, bufsize=bufsize

stdin=PIPE, stdout=PIPE, close_fds=True)

(child_stdout, child_stdin) = (p.stdout, p.stdin)

On Unix, popen2 also accepts a sequence as the command to execute, in

which case arguments will be passed directly to the program without

shell intervention. This usage can be replaced as follows:

(child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize,

mode)

==>

p = Popen(["mycmd", "myarg"], bufsize=bufsize,

stdin=PIPE, stdout=PIPE, close_fds=True)

(child_stdout, child_stdin) = (p.stdout, p.stdin)

The popen2.Popen3 and popen2.Popen4 basically works as subprocess.Popen,

except that:

* subprocess.Popen raises an exception if the execution fails

* the capturestderr argument is replaced with the stderr argument.

* stdin=PIPE and stdout=PIPE must be specified.

* popen2 closes all filedescriptors by default, but you have to specify

close_fds=True with subprocess.Popen.

"""

import sys

mswindows = (sys.platform == "win32")

import os

import types

import traceback

import gc

import signal

import errno

import ctypes

# Exception classes used by this module.

class CalledProcessError(Exception):

return "Command '%s' returned non-zero exit status %d" % (self.cmd, self.returncode)

if mswindows:

import threading

import msvcrt

import _subprocess

class STARTUPINFO:

wShowWindow = 0

class pywintypes:

error = IOError

else:

import select

_has_poll = hasattr(select, 'poll')

import fcntl

import pickle

# When select or poll has indicated that the file is writable,

# we can write up to _PIPE_BUF bytes without risk of blocking.

# POSIX defines PIPE_BUF as >= 512.

_PIPE_BUF = getattr(select, 'PIPE_BUF', 512)

__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call",

"check_output", "CalledProcessError"]

if mswindows:

from _subprocess import (CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP,

STD_INPUT_HANDLE, STD_OUTPUT_HANDLE,

STD_ERROR_HANDLE, SW_HIDE,

STARTF_USESTDHANDLES, STARTF_USESHOWWINDOW)

__all__.extend(["CREATE_NEW_CONSOLE", "CREATE_NEW_PROCESS_GROUP",

"STD_INPUT_HANDLE", "STD_OUTPUT_HANDLE",

"STD_ERROR_HANDLE", "SW_HIDE",

"STARTF_USESTDHANDLES", "STARTF_USESHOWWINDOW"])

try:

MAXFD = os.sysconf("SC_OPEN_MAX")

except:

MAXFD = 256

_active = []

def _cleanup():

pass

PIPE = -1

STDOUT = -2

def _eintr_retry_call(func, *args):

raise

# XXX This function is only used by multiprocessing and the test suite,

# but it's here so that it can be imported when Python is compiled without

# threads.

def _args_from_interpreter_flags():

return args

def call(*popenargs, **kwargs):

return Popen(*popenargs, **kwargs).wait()

def check_call(*popenargs, **kwargs):

return 0

def check_output(*popenargs, **kwargs):

return output

def list2cmdline(seq):

return ''.join(result)

if mswindows:

import platform

if platform.machine() == 'AMD64':

from ctypes import c_ulonglong as handleType

elif platform.machine() == 'i386':

from ctypes import c_uint as handleType

class STARTUP_INFO(ctypes.Structure):

("hStdError", ctypes.c_ulonglong)]

class PROCESS_INFORMATION(ctypes.Structure):

("dwThreadId", ctypes.c_uint)]

class Popen(object):