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ReStructuredText
1111 lines
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ReStructuredText
:mod:`subprocess` --- Subprocess management
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===========================================
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.. module:: subprocess
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:synopsis: Subprocess management.
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.. moduleauthor:: Peter Åstrand <astrand@lysator.liu.se>
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.. sectionauthor:: Peter Åstrand <astrand@lysator.liu.se>
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The :mod:`subprocess` module allows you to spawn new processes, connect to their
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input/output/error pipes, and obtain their return codes. This module intends to
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replace several other, older modules and functions, such as::
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os.system
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os.spawn*
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Information about how the :mod:`subprocess` module can be used to replace these
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modules and functions can be found in the following sections.
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.. seealso::
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:pep:`324` -- PEP proposing the subprocess module
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Using the :mod:`subprocess` Module
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----------------------------------
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The recommended approach to invoking subprocesses is to use the following
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convenience functions for all use cases they can handle. For more advanced
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use cases, the underlying :class:`Popen` interface can be used directly.
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.. function:: call(args, *, stdin=None, stdout=None, stderr=None, shell=False, timeout=None)
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Run the command described by *args*. Wait for command to complete, then
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return the :attr:`returncode` attribute.
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The arguments shown above are merely the most common ones, described below
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in :ref:`frequently-used-arguments` (hence the use of keyword-only notation
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in the abbreviated signature). The full function signature is largely the
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same as that of the :class:`Popen` constructor - this function passes all
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supplied arguments other than *timeout* directly through to that interface.
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The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout
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expires, the child process will be killed and then waited for again. The
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:exc:`TimeoutExpired` exception will be re-raised after the child process
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has terminated.
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Examples::
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>>> subprocess.call(["ls", "-l"])
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0
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>>> subprocess.call("exit 1", shell=True)
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1
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.. warning::
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Invoking the system shell with ``shell=True`` can be a security hazard
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if combined with untrusted input. See the warning under
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:ref:`frequently-used-arguments` for details.
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.. note::
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Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As
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the pipes are not being read in the current process, the child
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process may block if it generates enough output to a pipe to fill up
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the OS pipe buffer.
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.. versionchanged:: 3.3
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*timeout* was added.
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.. function:: check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, timeout=None)
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Run command with arguments. Wait for command to complete. If the return
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code was zero then return, otherwise raise :exc:`CalledProcessError`. The
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:exc:`CalledProcessError` object will have the return code in the
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:attr:`returncode` attribute.
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The arguments shown above are merely the most common ones, described below
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in :ref:`frequently-used-arguments` (hence the use of keyword-only notation
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in the abbreviated signature). The full function signature is largely the
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same as that of the :class:`Popen` constructor - this function passes all
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supplied arguments other than *timeout* directly through to that interface.
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The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout
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expires, the child process will be killed and then waited for again. The
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:exc:`TimeoutExpired` exception will be re-raised after the child process
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has terminated.
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Examples::
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>>> subprocess.check_call(["ls", "-l"])
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0
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>>> subprocess.check_call("exit 1", shell=True)
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Traceback (most recent call last):
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...
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subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1
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.. warning::
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Invoking the system shell with ``shell=True`` can be a security hazard
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if combined with untrusted input. See the warning under
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:ref:`frequently-used-arguments` for details.
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.. note::
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Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As
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the pipes are not being read in the current process, the child
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process may block if it generates enough output to a pipe to fill up
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the OS pipe buffer.
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.. versionchanged:: 3.3
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*timeout* was added.
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.. function:: check_output(args, *, stdin=None, stderr=None, shell=False, universal_newlines=False, timeout=None)
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Run command with arguments and return its output as a byte string.
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If the return code was non-zero it raises a :exc:`CalledProcessError`. The
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:exc:`CalledProcessError` object will have the return code in the
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:attr:`returncode` attribute and any output in the :attr:`output`
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attribute.
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The arguments shown above are merely the most common ones, described below
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in :ref:`frequently-used-arguments` (hence the use of keyword-only notation
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in the abbreviated signature). The full function signature is largely the
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same as that of the :class:`Popen` constructor - this functions passes all
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supplied arguments other than *timeout* directly through to that interface.
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In addition, *stdout* is not permitted as an argument, as it is used
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internally to collect the output from the subprocess.
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The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout
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expires, the child process will be killed and then waited for again. The
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:exc:`TimeoutExpired` exception will be re-raised after the child process
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has terminated.
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Examples::
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>>> subprocess.check_output(["echo", "Hello World!"])
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b'Hello World!\n'
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>>> subprocess.check_output(["echo", "Hello World!"], universal_newlines=True)
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'Hello World!\n'
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>>> subprocess.check_output("exit 1", shell=True)
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Traceback (most recent call last):
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...
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subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1
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By default, this function will return the data as encoded bytes. The actual
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encoding of the output data may depend on the command being invoked, so the
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decoding to text will often need to be handled at the application level.
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This behaviour may be overridden by setting *universal_newlines* to
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``True`` as described below in :ref:`frequently-used-arguments`.
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To also capture standard error in the result, use
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``stderr=subprocess.STDOUT``::
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>>> subprocess.check_output(
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... "ls non_existent_file; exit 0",
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... stderr=subprocess.STDOUT,
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... shell=True)
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'ls: non_existent_file: No such file or directory\n'
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.. versionadded:: 3.1
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.. warning::
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Invoking the system shell with ``shell=True`` can be a security hazard
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if combined with untrusted input. See the warning under
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:ref:`frequently-used-arguments` for details.
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.. note::
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Do not use ``stderr=PIPE`` with this function. As the pipe is not being
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read in the current process, the child process may block if it
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generates enough output to the pipe to fill up the OS pipe buffer.
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.. versionchanged:: 3.3
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*timeout* was added.
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.. data:: DEVNULL
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Special value that can be used as the *stdin*, *stdout* or *stderr* argument
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to :class:`Popen` and indicates that the special file :data:`os.devnull`
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will be used.
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.. versionadded:: 3.3
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.. data:: PIPE
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Special value that can be used as the *stdin*, *stdout* or *stderr* argument
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to :class:`Popen` and indicates that a pipe to the standard stream should be
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opened.
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.. data:: STDOUT
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Special value that can be used as the *stderr* argument to :class:`Popen` and
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indicates that standard error should go into the same handle as standard
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output.
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.. exception:: SubprocessError
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Base class for all other exceptions from this module.
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.. versionadded:: 3.3
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.. exception:: TimeoutExpired
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Subclass of :exc:`SubprocessError`, raised when a timeout expires
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while waiting for a child process.
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.. attribute:: cmd
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Command that was used to spawn the child process.
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.. attribute:: timeout
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Timeout in seconds.
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.. attribute:: output
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Output of the child process if this exception is raised by
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:func:`check_output`. Otherwise, ``None``.
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.. versionadded:: 3.3
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.. exception:: CalledProcessError
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Subclass of :exc:`SubprocessError`, raised when a process run by
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:func:`check_call` or :func:`check_output` returns a non-zero exit status.
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.. attribute:: returncode
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Exit status of the child process.
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.. attribute:: cmd
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Command that was used to spawn the child process.
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.. attribute:: output
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Output of the child process if this exception is raised by
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:func:`check_output`. Otherwise, ``None``.
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.. _frequently-used-arguments:
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Frequently Used Arguments
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^^^^^^^^^^^^^^^^^^^^^^^^^
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To support a wide variety of use cases, the :class:`Popen` constructor (and
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the convenience functions) accept a large number of optional arguments. For
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most typical use cases, many of these arguments can be safely left at their
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default values. The arguments that are most commonly needed are:
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*args* is required for all calls and should be a string, or a sequence of
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program arguments. Providing a sequence of arguments is generally
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preferred, as it allows the module to take care of any required escaping
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and quoting of arguments (e.g. to permit spaces in file names). If passing
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a single string, either *shell* must be :const:`True` (see below) or else
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the string must simply name the program to be executed without specifying
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any arguments.
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*stdin*, *stdout* and *stderr* specify the executed program's standard input,
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standard output and standard error file handles, respectively. Valid values
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are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive
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integer), an existing file object, and ``None``. :data:`PIPE` indicates
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that a new pipe to the child should be created. :data:`DEVNULL` indicates
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that the special file :data:`os.devnull` will be used. With the default
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settings of ``None``, no redirection will occur; the child's file handles
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will be inherited from the parent. Additionally, *stderr* can be
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:data:`STDOUT`, which indicates that the stderr data from the child
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process should be captured into the same file handle as for *stdout*.
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.. index::
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single: universal newlines; subprocess module
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If *universal_newlines* is ``True``, the file objects *stdin*, *stdout* and
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*stderr* will be opened as text streams in :term:`universal newlines` mode
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using the encoding returned by :func:`locale.getpreferredencoding(False)
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<locale.getpreferredencoding>`. For *stdin*, line ending characters
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``'\n'`` in the input will be converted to the default line separator
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:data:`os.linesep`. For *stdout* and *stderr*, all line endings in the
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output will be converted to ``'\n'``. For more information see the
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documentation of the :class:`io.TextIOWrapper` class when the *newline*
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argument to its constructor is ``None``.
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.. note::
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The *universal_newlines* feature is supported only if Python is built
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with universal newline support (the default). Also, the newlines
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attribute of the file objects :attr:`Popen.stdin`, :attr:`Popen.stdout`
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and :attr:`Popen.stderr` are not updated by the
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:meth:`Popen.communicate` method.
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If *shell* is ``True``, the specified command will be executed through
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the shell. This can be useful if you are using Python primarily for the
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enhanced control flow it offers over most system shells and still want
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convenient access to other shell features such as shell pipes, filename
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wildcards, environment variable expansion, and expansion of ``~`` to a
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user's home directory. However, note that Python itself offers
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implementations of many shell-like features (in particular, :mod:`glob`,
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:mod:`fnmatch`, :func:`os.walk`, :func:`os.path.expandvars`,
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:func:`os.path.expanduser`, and :mod:`shutil`).
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.. versionchanged:: 3.3
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When *universal_newlines* is ``True``, the class uses the encoding
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:func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`
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instead of ``locale.getpreferredencoding()``. See the
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:class:`io.TextIOWrapper` class for more information on this change.
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.. warning::
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Executing shell commands that incorporate unsanitized input from an
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untrusted source makes a program vulnerable to `shell injection
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<http://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_,
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a serious security flaw which can result in arbitrary command execution.
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For this reason, the use of ``shell=True`` is **strongly discouraged**
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in cases where the command string is constructed from external input::
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>>> from subprocess import call
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>>> filename = input("What file would you like to display?\n")
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What file would you like to display?
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non_existent; rm -rf / #
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>>> call("cat " + filename, shell=True) # Uh-oh. This will end badly...
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``shell=False`` disables all shell based features, but does not suffer
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from this vulnerability; see the Note in the :class:`Popen` constructor
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documentation for helpful hints in getting ``shell=False`` to work.
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When using ``shell=True``, :func:`shlex.quote` can be used to properly
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escape whitespace and shell metacharacters in strings that are going to
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be used to construct shell commands.
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These options, along with all of the other options, are described in more
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detail in the :class:`Popen` constructor documentation.
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Popen Constructor
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^^^^^^^^^^^^^^^^^
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The underlying process creation and management in this module is handled by
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the :class:`Popen` class. It offers a lot of flexibility so that developers
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are able to handle the less common cases not covered by the convenience
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functions.
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.. class:: Popen(args, bufsize=0, executable=None, stdin=None, stdout=None, \
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stderr=None, preexec_fn=None, close_fds=True, shell=False, \
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cwd=None, env=None, universal_newlines=False, \
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startupinfo=None, creationflags=0, restore_signals=True, \
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start_new_session=False, pass_fds=())
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Execute a child program in a new process. On Unix, the class uses
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:meth:`os.execvp`-like behavior to execute the child program. On Windows,
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the class uses the Windows ``CreateProcess()`` function. The arguments to
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:class:`Popen` are as follows.
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*args* should be a sequence of program arguments or else a single string.
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By default, the program to execute is the first item in *args* if *args* is
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a sequence. If *args* is a string, the interpretation is
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platform-dependent and described below. See the *shell* and *executable*
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arguments for additional differences from the default behavior. Unless
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otherwise stated, it is recommended to pass *args* as a sequence.
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On Unix, if *args* is a string, the string is interpreted as the name or
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path of the program to execute. However, this can only be done if not
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passing arguments to the program.
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.. note::
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:meth:`shlex.split` can be useful when determining the correct
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tokenization for *args*, especially in complex cases::
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>>> import shlex, subprocess
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>>> command_line = input()
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/bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'"
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>>> args = shlex.split(command_line)
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>>> print(args)
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['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"]
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>>> p = subprocess.Popen(args) # Success!
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Note in particular that options (such as *-input*) and arguments (such
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as *eggs.txt*) that are separated by whitespace in the shell go in separate
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list elements, while arguments that need quoting or backslash escaping when
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used in the shell (such as filenames containing spaces or the *echo* command
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shown above) are single list elements.
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On Windows, if *args* is a sequence, it will be converted to a string in a
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manner described in :ref:`converting-argument-sequence`. This is because
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the underlying ``CreateProcess()`` operates on strings.
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The *shell* argument (which defaults to *False*) specifies whether to use
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the shell as the program to execute. If *shell* is *True*, it is
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recommended to pass *args* as a string rather than as a sequence.
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On Unix with ``shell=True``, the shell defaults to :file:`/bin/sh`. If
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*args* is a string, the string specifies the command
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to execute through the shell. This means that the string must be
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formatted exactly as it would be when typed at the shell prompt. This
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includes, for example, quoting or backslash escaping filenames with spaces in
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them. If *args* is a sequence, the first item specifies the command string, and
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any additional items will be treated as additional arguments to the shell
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itself. That is to say, :class:`Popen` does the equivalent of::
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Popen(['/bin/sh', '-c', args[0], args[1], ...])
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On Windows with ``shell=True``, the :envvar:`COMSPEC` environment variable
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specifies the default shell. The only time you need to specify
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``shell=True`` on Windows is when the command you wish to execute is built
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into the shell (e.g. :command:`dir` or :command:`copy`). You do not need
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``shell=True`` to run a batch file or console-based executable.
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.. warning::
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Passing ``shell=True`` can be a security hazard if combined with
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untrusted input. See the warning under :ref:`frequently-used-arguments`
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for details.
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*bufsize*, if given, has the same meaning as the corresponding argument to the
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built-in open() function: :const:`0` means unbuffered, :const:`1` means line
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buffered, any other positive value means use a buffer of (approximately) that
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size. A negative *bufsize* means to use the system default, which usually means
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fully buffered. The default value for *bufsize* is :const:`0` (unbuffered).
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.. note::
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If you experience performance issues, it is recommended that you try to
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enable buffering by setting *bufsize* to either -1 or a large enough
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positive value (such as 4096).
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The *executable* argument specifies a replacement program to execute. It
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is very seldom needed. When ``shell=False``, *executable* replaces the
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program to execute specified by *args*. However, the original *args* is
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still passed to the program. Most programs treat the program specified
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by *args* as the command name, which can then be different from the program
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actually executed. On Unix, the *args* name
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becomes the display name for the executable in utilities such as
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:program:`ps`. If ``shell=True``, on Unix the *executable* argument
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specifies a replacement shell for the default :file:`/bin/sh`.
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*stdin*, *stdout* and *stderr* specify the executed program's standard input,
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standard output and standard error file handles, respectively. Valid values
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are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive
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integer), an existing :term:`file object`, and ``None``. :data:`PIPE`
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indicates that a new pipe to the child should be created. :data:`DEVNULL`
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indicates that the special file :data:`os.devnull` will be used. With the
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default settings of ``None``, no redirection will occur; the child's file
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handles will be inherited from the parent. Additionally, *stderr* can be
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:data:`STDOUT`, which indicates that the stderr data from the applications
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should be captured into the same file handle as for stdout.
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If *preexec_fn* is set to a callable object, this object will be called in the
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child process just before the child is executed.
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(Unix only)
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.. warning::
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The *preexec_fn* parameter is not safe to use in the presence of threads
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in your application. The child process could deadlock before exec is
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called.
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If you must use it, keep it trivial! Minimize the number of libraries
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you call into.
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.. note::
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If you need to modify the environment for the child use the *env*
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parameter rather than doing it in a *preexec_fn*.
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The *start_new_session* parameter can take the place of a previously
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common use of *preexec_fn* to call os.setsid() in the child.
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|
|
If *close_fds* is true, all file descriptors except :const:`0`, :const:`1` and
|
|
:const:`2` will be closed before the child process is executed. (Unix only).
|
|
The default varies by platform: Always true on Unix. On Windows it is
|
|
true when *stdin*/*stdout*/*stderr* are :const:`None`, false otherwise.
|
|
On Windows, if *close_fds* is true then no handles will be inherited by the
|
|
child process. Note that on Windows, you cannot set *close_fds* to true and
|
|
also redirect the standard handles by setting *stdin*, *stdout* or *stderr*.
|
|
|
|
.. versionchanged:: 3.2
|
|
The default for *close_fds* was changed from :const:`False` to
|
|
what is described above.
|
|
|
|
*pass_fds* is an optional sequence of file descriptors to keep open
|
|
between the parent and child. Providing any *pass_fds* forces
|
|
*close_fds* to be :const:`True`. (Unix only)
|
|
|
|
.. versionadded:: 3.2
|
|
The *pass_fds* parameter was added.
|
|
|
|
If *cwd* is not ``None``, the function changes the working directory to
|
|
*cwd* before executing the child. In particular, the function looks for
|
|
*executable* (or for the first item in *args*) relative to *cwd* if the
|
|
executable path is a relative path.
|
|
|
|
If *restore_signals* is True (the default) all signals that Python has set to
|
|
SIG_IGN are restored to SIG_DFL in the child process before the exec.
|
|
Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals.
|
|
(Unix only)
|
|
|
|
.. versionchanged:: 3.2
|
|
*restore_signals* was added.
|
|
|
|
If *start_new_session* is True the setsid() system call will be made in the
|
|
child process prior to the execution of the subprocess. (Unix only)
|
|
|
|
.. versionchanged:: 3.2
|
|
*start_new_session* was added.
|
|
|
|
If *env* is not ``None``, it must be a mapping that defines the environment
|
|
variables for the new process; these are used instead of the default
|
|
behavior of inheriting the current process' environment.
|
|
|
|
.. note::
|
|
|
|
If specified, *env* must provide any variables required for the program to
|
|
execute. On Windows, in order to run a `side-by-side assembly`_ the
|
|
specified *env* **must** include a valid :envvar:`SystemRoot`.
|
|
|
|
.. _side-by-side assembly: http://en.wikipedia.org/wiki/Side-by-Side_Assembly
|
|
|
|
If *universal_newlines* is ``True``, the file objects *stdin*, *stdout*
|
|
and *stderr* are opened as text streams in universal newlines mode, as
|
|
described above in :ref:`frequently-used-arguments`.
|
|
|
|
If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is
|
|
passed to the underlying ``CreateProcess`` function.
|
|
*creationflags*, if given, can be :data:`CREATE_NEW_CONSOLE` or
|
|
:data:`CREATE_NEW_PROCESS_GROUP`. (Windows only)
|
|
|
|
Popen objects are supported as context managers via the :keyword:`with` statement:
|
|
on exit, standard file descriptors are closed, and the process is waited for.
|
|
::
|
|
|
|
with Popen(["ifconfig"], stdout=PIPE) as proc:
|
|
log.write(proc.stdout.read())
|
|
|
|
.. versionchanged:: 3.2
|
|
Added context manager support.
|
|
|
|
|
|
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 :attr:`child_traceback`, which is a string
|
|
containing traceback information from the child's point of view.
|
|
|
|
The most common exception raised is :exc:`OSError`. This occurs, for example,
|
|
when trying to execute a non-existent file. Applications should prepare for
|
|
:exc:`OSError` exceptions.
|
|
|
|
A :exc:`ValueError` will be raised if :class:`Popen` is called with invalid
|
|
arguments.
|
|
|
|
:func:`check_call` and :func:`check_output` will raise
|
|
:exc:`CalledProcessError` if the called process returns a non-zero return
|
|
code.
|
|
|
|
All of the functions and methods that accept a *timeout* parameter, such as
|
|
:func:`call` and :meth:`Popen.communicate` will raise :exc:`TimeoutExpired` if
|
|
the timeout expires before the process exits.
|
|
|
|
Exceptions defined in this module all inherit from :exc:`SubprocessError`.
|
|
|
|
.. versionadded:: 3.3
|
|
The :exc:`SubprocessError` base class was added.
|
|
|
|
|
|
Security
|
|
^^^^^^^^
|
|
|
|
Unlike some other popen functions, this implementation will never call a
|
|
system shell implicitly. This means that all characters, including shell
|
|
metacharacters, can safely be passed to child processes. Obviously, if the
|
|
shell is invoked explicitly, then it is the application's responsibility to
|
|
ensure that all whitespace and metacharacters are quoted appropriately.
|
|
|
|
|
|
Popen Objects
|
|
-------------
|
|
|
|
Instances of the :class:`Popen` class have the following methods:
|
|
|
|
|
|
.. method:: Popen.poll()
|
|
|
|
Check if child process has terminated. Set and return :attr:`returncode`
|
|
attribute.
|
|
|
|
|
|
.. method:: Popen.wait(timeout=None)
|
|
|
|
Wait for child process to terminate. Set and return :attr:`returncode`
|
|
attribute.
|
|
|
|
If the process does not terminate after *timeout* seconds, raise a
|
|
:exc:`TimeoutExpired` exception. It is safe to catch this exception and
|
|
retry the wait.
|
|
|
|
.. warning::
|
|
|
|
This will deadlock when using ``stdout=PIPE`` and/or
|
|
``stderr=PIPE`` and the child process generates enough output to
|
|
a pipe such that it blocks waiting for the OS pipe buffer to
|
|
accept more data. Use :meth:`communicate` to avoid that.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. method:: Popen.communicate(input=None, timeout=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 data to be sent to the child process, or
|
|
``None``, if no data should be sent to the child. The type of *input*
|
|
must be bytes or, if *universal_newlines* was ``True``, a string.
|
|
|
|
:meth:`communicate` returns a tuple ``(stdoutdata, stderrdata)``.
|
|
|
|
Note that if you want to send data to the process's stdin, you need to create
|
|
the Popen object with ``stdin=PIPE``. Similarly, to get anything other than
|
|
``None`` in the result tuple, you need to give ``stdout=PIPE`` and/or
|
|
``stderr=PIPE`` too.
|
|
|
|
If the process does not terminate after *timeout* seconds, a
|
|
:exc:`TimeoutExpired` exception will be raised. Catching this exception and
|
|
retrying communication will not lose any output.
|
|
|
|
The child process is not killed if the timeout expires, so in order to
|
|
cleanup properly a well-behaved application should kill the child process and
|
|
finish communication::
|
|
|
|
proc = subprocess.Popen(...)
|
|
try:
|
|
outs, errs = proc.communicate(timeout=15)
|
|
except TimeoutExpired:
|
|
proc.kill()
|
|
outs, errs = proc.communicate()
|
|
|
|
.. note::
|
|
|
|
The data read is buffered in memory, so do not use this method if the data
|
|
size is large or unlimited.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. method:: Popen.send_signal(signal)
|
|
|
|
Sends the signal *signal* to the child.
|
|
|
|
.. note::
|
|
|
|
On Windows, SIGTERM is an alias for :meth:`terminate`. CTRL_C_EVENT and
|
|
CTRL_BREAK_EVENT can be sent to processes started with a *creationflags*
|
|
parameter which includes `CREATE_NEW_PROCESS_GROUP`.
|
|
|
|
|
|
.. method:: Popen.terminate()
|
|
|
|
Stop the child. On Posix OSs the method sends SIGTERM to the
|
|
child. On Windows the Win32 API function :c:func:`TerminateProcess` is called
|
|
to stop the child.
|
|
|
|
|
|
.. method:: Popen.kill()
|
|
|
|
Kills the child. On Posix OSs the function sends SIGKILL to the child.
|
|
On Windows :meth:`kill` is an alias for :meth:`terminate`.
|
|
|
|
|
|
The following attributes are also available:
|
|
|
|
.. warning::
|
|
|
|
Use :meth:`~Popen.communicate` rather than :attr:`.stdin.write <Popen.stdin>`,
|
|
:attr:`.stdout.read <Popen.stdout>` or :attr:`.stderr.read <Popen.stderr>` to avoid
|
|
deadlocks due to any of the other OS pipe buffers filling up and blocking the
|
|
child process.
|
|
|
|
|
|
.. attribute:: Popen.stdin
|
|
|
|
If the *stdin* argument was :data:`PIPE`, this attribute is a :term:`file
|
|
object` that provides input to the child process. Otherwise, it is ``None``.
|
|
|
|
|
|
.. attribute:: Popen.stdout
|
|
|
|
If the *stdout* argument was :data:`PIPE`, this attribute is a :term:`file
|
|
object` that provides output from the child process. Otherwise, it is ``None``.
|
|
|
|
|
|
.. attribute:: Popen.stderr
|
|
|
|
If the *stderr* argument was :data:`PIPE`, this attribute is a :term:`file
|
|
object` that provides error output from the child process. Otherwise, it is
|
|
``None``.
|
|
|
|
|
|
.. attribute:: Popen.pid
|
|
|
|
The process ID of the child process.
|
|
|
|
Note that if you set the *shell* argument to ``True``, this is the process ID
|
|
of the spawned shell.
|
|
|
|
|
|
.. attribute:: Popen.returncode
|
|
|
|
The child return code, set by :meth:`poll` and :meth:`wait` (and indirectly
|
|
by :meth:`communicate`). 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).
|
|
|
|
|
|
Windows Popen Helpers
|
|
---------------------
|
|
|
|
The :class:`STARTUPINFO` class and following constants are only available
|
|
on Windows.
|
|
|
|
.. class:: STARTUPINFO()
|
|
|
|
Partial support of the Windows
|
|
`STARTUPINFO <http://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx>`__
|
|
structure is used for :class:`Popen` creation.
|
|
|
|
.. attribute:: dwFlags
|
|
|
|
A bit field that determines whether certain :class:`STARTUPINFO`
|
|
attributes are used when the process creates a window. ::
|
|
|
|
si = subprocess.STARTUPINFO()
|
|
si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW
|
|
|
|
.. attribute:: hStdInput
|
|
|
|
If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute
|
|
is the standard input handle for the process. If
|
|
:data:`STARTF_USESTDHANDLES` is not specified, the default for standard
|
|
input is the keyboard buffer.
|
|
|
|
.. attribute:: hStdOutput
|
|
|
|
If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute
|
|
is the standard output handle for the process. Otherwise, this attribute
|
|
is ignored and the default for standard output is the console window's
|
|
buffer.
|
|
|
|
.. attribute:: hStdError
|
|
|
|
If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute
|
|
is the standard error handle for the process. Otherwise, this attribute is
|
|
ignored and the default for standard error is the console window's buffer.
|
|
|
|
.. attribute:: wShowWindow
|
|
|
|
If :attr:`dwFlags` specifies :data:`STARTF_USESHOWWINDOW`, this attribute
|
|
can be any of the values that can be specified in the ``nCmdShow``
|
|
parameter for the
|
|
`ShowWindow <http://msdn.microsoft.com/en-us/library/ms633548(v=vs.85).aspx>`__
|
|
function, except for ``SW_SHOWDEFAULT``. Otherwise, this attribute is
|
|
ignored.
|
|
|
|
:data:`SW_HIDE` is provided for this attribute. It is used when
|
|
:class:`Popen` is called with ``shell=True``.
|
|
|
|
|
|
Constants
|
|
^^^^^^^^^
|
|
|
|
The :mod:`subprocess` module exposes the following constants.
|
|
|
|
.. data:: STD_INPUT_HANDLE
|
|
|
|
The standard input device. Initially, this is the console input buffer,
|
|
``CONIN$``.
|
|
|
|
.. data:: STD_OUTPUT_HANDLE
|
|
|
|
The standard output device. Initially, this is the active console screen
|
|
buffer, ``CONOUT$``.
|
|
|
|
.. data:: STD_ERROR_HANDLE
|
|
|
|
The standard error device. Initially, this is the active console screen
|
|
buffer, ``CONOUT$``.
|
|
|
|
.. data:: SW_HIDE
|
|
|
|
Hides the window. Another window will be activated.
|
|
|
|
.. data:: STARTF_USESTDHANDLES
|
|
|
|
Specifies that the :attr:`STARTUPINFO.hStdInput`,
|
|
:attr:`STARTUPINFO.hStdOutput`, and :attr:`STARTUPINFO.hStdError` attributes
|
|
contain additional information.
|
|
|
|
.. data:: STARTF_USESHOWWINDOW
|
|
|
|
Specifies that the :attr:`STARTUPINFO.wShowWindow` attribute contains
|
|
additional information.
|
|
|
|
.. data:: CREATE_NEW_CONSOLE
|
|
|
|
The new process has a new console, instead of inheriting its parent's
|
|
console (the default).
|
|
|
|
This flag is always set when :class:`Popen` is created with ``shell=True``.
|
|
|
|
.. data:: CREATE_NEW_PROCESS_GROUP
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
group will be created. This flag is necessary for using :func:`os.kill`
|
|
on the subprocess.
|
|
|
|
This flag is ignored if :data:`CREATE_NEW_CONSOLE` is specified.
|
|
|
|
|
|
.. _subprocess-replacements:
|
|
|
|
Replacing Older Functions with the :mod:`subprocess` Module
|
|
-----------------------------------------------------------
|
|
|
|
In this section, "a becomes b" means that b can be used as a replacement for a.
|
|
|
|
.. note::
|
|
|
|
All "a" functions in this section fail (more or less) silently if the
|
|
executed program cannot be found; the "b" replacements raise :exc:`OSError`
|
|
instead.
|
|
|
|
In addition, the replacements using :func:`check_output` will fail with a
|
|
:exc:`CalledProcessError` if the requested operation produces a non-zero
|
|
return code. The output is still available as the ``output`` attribute of
|
|
the raised exception.
|
|
|
|
In the following examples, we assume that the relevant functions have already
|
|
been imported from the :mod:`subprocess` module.
|
|
|
|
|
|
Replacing /bin/sh shell backquote
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
output=`mycmd myarg`
|
|
# becomes
|
|
output = check_output(["mycmd", "myarg"])
|
|
|
|
|
|
Replacing shell pipeline
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
output=`dmesg | grep hda`
|
|
# becomes
|
|
p1 = Popen(["dmesg"], stdout=PIPE)
|
|
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
|
|
p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits.
|
|
output = p2.communicate()[0]
|
|
|
|
The p1.stdout.close() call after starting the p2 is important in order for p1
|
|
to receive a SIGPIPE if p2 exits before p1.
|
|
|
|
Alternatively, for trusted input, the shell's own pipeline support may still
|
|
be used directly::
|
|
|
|
output=`dmesg | grep hda`
|
|
# becomes
|
|
output=check_output("dmesg | grep hda", shell=True)
|
|
|
|
|
|
Replacing :func:`os.system`
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
sts = os.system("mycmd" + " myarg")
|
|
# becomes
|
|
sts = call("mycmd" + " myarg", shell=True)
|
|
|
|
Notes:
|
|
|
|
* Calling the program through the shell is usually not required.
|
|
|
|
A more realistic example would look like this::
|
|
|
|
try:
|
|
retcode = call("mycmd" + " myarg", shell=True)
|
|
if retcode < 0:
|
|
print("Child was terminated by signal", -retcode, file=sys.stderr)
|
|
else:
|
|
print("Child returned", retcode, file=sys.stderr)
|
|
except OSError as e:
|
|
print("Execution failed:", e, file=sys.stderr)
|
|
|
|
|
|
Replacing the :func:`os.spawn <os.spawnl>` family
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
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 :func:`os.popen`, :func:`os.popen2`, :func:`os.popen3`
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
(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)
|
|
|
|
Return code handling translates as follows::
|
|
|
|
pipe = os.popen(cmd, 'w')
|
|
...
|
|
rc = pipe.close()
|
|
if rc is not None and rc >> 8:
|
|
print("There were some errors")
|
|
==>
|
|
process = Popen(cmd, 'w', stdin=PIPE)
|
|
...
|
|
process.stdin.close()
|
|
if process.wait() != 0:
|
|
print("There were some errors")
|
|
|
|
|
|
Replacing functions from the :mod:`popen2` module
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
.. 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)
|
|
|
|
:class:`popen2.Popen3` and :class:`popen2.Popen4` basically work as
|
|
:class:`subprocess.Popen`, except that:
|
|
|
|
* :class:`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 file descriptors by default, but you have to specify
|
|
``close_fds=True`` with :class:`Popen` to guarantee this behavior on
|
|
all platforms or past Python versions.
|
|
|
|
|
|
Legacy Shell Invocation Functions
|
|
---------------------------------
|
|
|
|
This module also provides the following legacy functions from the 2.x
|
|
``commands`` module. These operations implicitly invoke the system shell and
|
|
none of the guarantees described above regarding security and exception
|
|
handling consistency are valid for these functions.
|
|
|
|
.. function:: getstatusoutput(cmd)
|
|
|
|
Return ``(status, output)`` of executing *cmd* in a shell.
|
|
|
|
Execute the string *cmd* in a shell with :func:`os.popen` and return a 2-tuple
|
|
``(status, output)``. *cmd* is actually run as ``{ cmd ; } 2>&1``, so that the
|
|
returned output will contain output or error messages. A trailing newline is
|
|
stripped from the output. The exit status for the command can be interpreted
|
|
according to the rules for the C function :c:func:`wait`. Example::
|
|
|
|
>>> subprocess.getstatusoutput('ls /bin/ls')
|
|
(0, '/bin/ls')
|
|
>>> subprocess.getstatusoutput('cat /bin/junk')
|
|
(256, 'cat: /bin/junk: No such file or directory')
|
|
>>> subprocess.getstatusoutput('/bin/junk')
|
|
(256, 'sh: /bin/junk: not found')
|
|
|
|
Availability: UNIX.
|
|
|
|
|
|
.. function:: getoutput(cmd)
|
|
|
|
Return output (stdout and stderr) of executing *cmd* in a shell.
|
|
|
|
Like :func:`getstatusoutput`, except the exit status is ignored and the return
|
|
value is a string containing the command's output. Example::
|
|
|
|
>>> subprocess.getoutput('ls /bin/ls')
|
|
'/bin/ls'
|
|
|
|
Availability: UNIX.
|
|
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. _converting-argument-sequence:
|
|
|
|
Converting an argument sequence to a string on Windows
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
On Windows, an *args* sequence is converted to a string that can be parsed
|
|
using the following rules (which correspond to the rules used by 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.
|
|
|
|
|
|
.. seealso::
|
|
|
|
:mod:`shlex`
|
|
Module which provides function to parse and escape command lines.
|