# 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 two 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"])

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() 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)

Replacing popen2.*

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

Note: If the cmd argument to popen2 functions is a string, the command

is executed through /bin/sh.  If it is a list, the command is directly

executed.

(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)

(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

# Exception classes used by this module.

class CalledProcessError(Exception):

    """This exception is raised when a process run by check_call() returns

    a non-zero exit status.  The exit status will be stored in the

    returncode attribute."""

    def __init__(self, returncode, cmd):

        self.returncode = returncode

        self.cmd = cmd

    def __str__(self):

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

if mswindows:

    import threading

    import msvcrt

    if 0: # <-- change this to use pywin32 instead of the _subprocess driver

        import pywintypes

        from win32api import GetStdHandle, STD_INPUT_HANDLE, \

                             STD_OUTPUT_HANDLE, STD_ERROR_HANDLE

        from win32api import GetCurrentProcess, DuplicateHandle, \

                             GetModuleFileName, GetVersion

        from win32con import DUPLICATE_SAME_ACCESS, SW_HIDE

        from win32pipe import CreatePipe

        from win32process import CreateProcess, STARTUPINFO, \

                                 GetExitCodeProcess, STARTF_USESTDHANDLES, \

                                 STARTF_USESHOWWINDOW, CREATE_NEW_CONSOLE

        from win32event import WaitForSingleObject, INFINITE, WAIT_OBJECT_0

    else:

        from _subprocess import *

        class STARTUPINFO:

            dwFlags = 0

            hStdInput = None

            hStdOutput = None

            hStdError = None

            wShowWindow = 0

        class pywintypes:

            error = IOError

else:

    import select

    import errno

    import fcntl

    import pickle

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

try:

    MAXFD = os.sysconf("SC_OPEN_MAX")

except:

    MAXFD = 256

# True/False does not exist on 2.2.0

try:

    False

except NameError:

    False = 0

    True = 1

_active = []

def _cleanup():

    for inst in _active[:]:

        if inst.poll(_deadstate=sys.maxint) >= 0:

            try:

                _active.remove(inst)

            except ValueError:

                # This can happen if two threads create a new Popen instance.

                # It's harmless that it was already removed, so ignore.

                pass

PIPE = -1

STDOUT = -2

def 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"])

    """

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

def 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"])

    """

    retcode = call(*popenargs, **kwargs)

    cmd = kwargs.get("args")

    if cmd is None:

        cmd = popenargs[0]

    if retcode:

        raise CalledProcessError(retcode, cmd)

    return retcode

def list2cmdline(seq):

    """

    Translate a sequence of arguments into a command line

    string, using the same rules as the MS C runtime:

    1) Arguments are delimited by white space, which is either a

       space or a tab.

    2) A string surrounded by double quotation marks is

       interpreted as a single argument, regardless of white space

       contained within.  A quoted string can be embedded in an

       argument.

    3) A double quotation mark preceded by a backslash is

       interpreted as a literal double quotation mark.

    4) Backslashes are interpreted literally, unless they

       immediately precede a double quotation mark.

    5) If backslashes immediately precede a double quotation mark,

       every pair of backslashes is interpreted as a literal

       backslash.  If the number of backslashes is odd, the last

       backslash escapes the next double quotation mark as

       described in rule 3.

    """

    # See

    # http://msdn.microsoft.com/library/en-us/vccelng/htm/progs_12.asp

    result = []

    needquote = False

    for arg in seq:

        bs_buf = []

        # Add a space to separate this argument from the others

        if result:

            result.append(' ')

        needquote = (" " in arg) or ("\t" in arg) or arg == ""

        if needquote:

            result.append('"')

        for c in arg:

            if c == '\\':

                # Don't know if we need to double yet.

                bs_buf.append(c)

            elif c == '"':

                # Double backspaces.

                result.append('\\' * len(bs_buf)*2)

                bs_buf = []

                result.append('\\"')

            else:

                # Normal char

                if bs_buf:

                    result.extend(bs_buf)

                    bs_buf = []

                result.append(c)

        # Add remaining backspaces, if any.

        if bs_buf:

            result.extend(bs_buf)

        if needquote:

            result.extend(bs_buf)