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[doc] Make subprocess.wait doc more precise An active loop is only used when the `timeout` parameter is used on POSIX. When no timeout is used, the code calls `os.waitpid` internally (which puts the process on a sleep status). On Windows, the internal Windows API call accepts a timeout parameter, so that is delegated to the OS.
1639 lines
60 KiB
ReStructuredText
1639 lines
60 KiB
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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**Source code:** :source:`Lib/subprocess.py`
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--------------
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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 older modules and functions::
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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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.. include:: ../includes/wasm-notavail.rst
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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 :func:`run`
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function for all use cases it can handle. For more advanced use cases, the
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underlying :class:`Popen` interface can be used directly.
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.. function:: run(args, *, stdin=None, input=None, stdout=None, stderr=None,\
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capture_output=False, shell=False, cwd=None, timeout=None, \
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check=False, encoding=None, errors=None, text=None, env=None, \
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universal_newlines=None, **other_popen_kwargs)
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Run the command described by *args*. Wait for command to complete, then
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return a :class:`CompletedProcess` instance.
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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 - most of the arguments to
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this function are passed through to that interface. (*timeout*, *input*,
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*check*, and *capture_output* are not.)
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If *capture_output* is true, stdout and stderr will be captured.
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When used, the internal :class:`Popen` object is automatically created with
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``stdout=PIPE`` and ``stderr=PIPE``. The *stdout* and *stderr* arguments may
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not be supplied at the same time as *capture_output*. If you wish to capture
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and combine both streams into one, use ``stdout=PIPE`` and ``stderr=STDOUT``
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instead of *capture_output*.
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A *timeout* may be specified in seconds, it is internally passed on to
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:meth:`Popen.communicate`. If the timeout expires, the child process will be
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killed and waited for. The :exc:`TimeoutExpired` exception will be
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re-raised after the child process has terminated. The initial process
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creation itself cannot be interrupted on many platform APIs so you are not
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guaranteed to see a timeout exception until at least after however long
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process creation takes.
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The *input* argument is passed to :meth:`Popen.communicate` and thus to the
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subprocess's stdin. If used it must be a byte sequence, or a string if
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*encoding* or *errors* is specified or *text* is true. When
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used, the internal :class:`Popen` object is automatically created with
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``stdin=PIPE``, and the *stdin* argument may not be used as well.
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If *check* is true, and the process exits with a non-zero exit code, a
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:exc:`CalledProcessError` exception will be raised. Attributes of that
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exception hold the arguments, the exit code, and stdout and stderr if they
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were captured.
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If *encoding* or *errors* are specified, or *text* is true,
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file objects for stdin, stdout and stderr are opened in text mode using the
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specified *encoding* and *errors* or the :class:`io.TextIOWrapper` default.
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The *universal_newlines* argument is equivalent to *text* and is provided
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for backwards compatibility. By default, file objects are opened in binary mode.
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If *env* is not ``None``, it must be a mapping that defines the environment
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variables for the new process; these are used instead of the default
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behavior of inheriting the current process' environment. It is passed
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directly to :class:`Popen`. This mapping can be str to str on any platform
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or bytes to bytes on POSIX platforms much like :data:`os.environ` or
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:data:`os.environb`.
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Examples::
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>>> subprocess.run(["ls", "-l"]) # doesn't capture output
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CompletedProcess(args=['ls', '-l'], returncode=0)
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>>> subprocess.run("exit 1", shell=True, check=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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>>> subprocess.run(["ls", "-l", "/dev/null"], capture_output=True)
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CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
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stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n', stderr=b'')
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.. versionadded:: 3.5
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.. versionchanged:: 3.6
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Added *encoding* and *errors* parameters
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.. versionchanged:: 3.7
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Added the *text* parameter, as a more understandable alias of *universal_newlines*.
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Added the *capture_output* parameter.
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.. versionchanged:: 3.12
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Changed Windows shell search order for ``shell=True``. The current
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directory and ``%PATH%`` are replaced with ``%COMSPEC%`` and
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``%SystemRoot%\System32\cmd.exe``. As a result, dropping a
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malicious program named ``cmd.exe`` into a current directory no
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longer works.
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.. class:: CompletedProcess
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The return value from :func:`run`, representing a process that has finished.
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.. attribute:: args
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The arguments used to launch the process. This may be a list or a string.
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.. attribute:: returncode
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Exit status of the child process. Typically, an exit status of 0 indicates
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that it ran successfully.
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A negative value ``-N`` indicates that the child was terminated by signal
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``N`` (POSIX only).
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.. attribute:: stdout
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Captured stdout from the child process. A bytes sequence, or a string if
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:func:`run` was called with an encoding, errors, or text=True.
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``None`` if stdout was not captured.
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If you ran the process with ``stderr=subprocess.STDOUT``, stdout and
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stderr will be combined in this attribute, and :attr:`stderr` will be
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``None``.
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.. attribute:: stderr
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Captured stderr from the child process. A bytes sequence, or a string if
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:func:`run` was called with an encoding, errors, or text=True.
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``None`` if stderr was not captured.
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.. method:: check_returncode()
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If :attr:`returncode` is non-zero, raise a :exc:`CalledProcessError`.
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.. versionadded:: 3.5
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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. Most useful with :meth:`Popen.communicate`.
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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 it was captured by :func:`run` or
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:func:`check_output`. Otherwise, ``None``. This is always
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:class:`bytes` when any output was captured regardless of the
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``text=True`` setting. It may remain ``None`` instead of ``b''``
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when no output was observed.
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.. attribute:: stdout
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Alias for output, for symmetry with :attr:`stderr`.
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.. attribute:: stderr
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Stderr output of the child process if it was captured by :func:`run`.
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Otherwise, ``None``. This is always :class:`bytes` when stderr output
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was captured regardless of the ``text=True`` setting. It may remain
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``None`` instead of ``b''`` when no stderr output was observed.
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.. versionadded:: 3.3
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.. versionchanged:: 3.5
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*stdout* and *stderr* attributes added
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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`, :func:`check_output`, or :func:`run` (with ``check=True``)
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returns a non-zero exit status.
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.. attribute:: returncode
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Exit status of the child process. If the process exited due to a
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signal, this will be the negative signal number.
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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 it was captured by :func:`run` or
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:func:`check_output`. Otherwise, ``None``.
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.. attribute:: stdout
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Alias for output, for symmetry with :attr:`stderr`.
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.. attribute:: stderr
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Stderr output of the child process if it was captured by :func:`run`.
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Otherwise, ``None``.
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.. versionchanged:: 3.5
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*stdout* and *stderr* attributes added
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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 ``None``, :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a
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positive integer), and an existing :term:`file object` with a valid file
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descriptor. With the default settings of ``None``, no redirection will
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occur. :data:`PIPE` indicates that a new pipe to the child should be
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created. :data:`DEVNULL` indicates that the special file :data:`os.devnull`
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will be used. Additionally, *stderr* can be :data:`STDOUT`, which indicates
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that the stderr data from the child process should be captured into the same
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file handle as for *stdout*.
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.. index::
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single: universal newlines; subprocess module
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If *encoding* or *errors* are specified, or *text* (also known as
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*universal_newlines*) is true,
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the file objects *stdin*, *stdout* and *stderr* will be opened in text
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mode using the *encoding* and *errors* specified in the call or the
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defaults for :class:`io.TextIOWrapper`.
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For *stdin*, line ending characters ``'\n'`` in the input will be converted
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to the default line separator :data:`os.linesep`. For *stdout* and *stderr*,
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all line endings in the output will be converted to ``'\n'``. For more
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information see the documentation of the :class:`io.TextIOWrapper` class
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when the *newline* argument to its constructor is ``None``.
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If text mode is not used, *stdin*, *stdout* and *stderr* will be opened as
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binary streams. No encoding or line ending conversion is performed.
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.. versionadded:: 3.6
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Added *encoding* and *errors* parameters.
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.. versionadded:: 3.7
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Added the *text* parameter as an alias for *universal_newlines*.
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.. note::
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The newlines attribute of the file objects :attr:`Popen.stdin`,
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:attr:`Popen.stdout` and :attr:`Popen.stderr` are not updated by
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the :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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.. note::
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Read the `Security Considerations`_ section before using ``shell=True``.
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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=-1, 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=None, \
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startupinfo=None, creationflags=0, restore_signals=True, \
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start_new_session=False, pass_fds=(), *, group=None, \
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extra_groups=None, user=None, umask=-1, \
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encoding=None, errors=None, text=None, pipesize=-1, \
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process_group=None)
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Execute a child program in a new process. On POSIX, the class uses
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:meth:`os.execvpe`-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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or :term:`path-like object`.
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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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.. warning::
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For maximum reliability, use a fully qualified path for the executable.
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To search for an unqualified name on :envvar:`PATH`, use
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:meth:`shutil.which`. On all platforms, passing :data:`sys.executable`
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is the recommended way to launch the current Python interpreter again,
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and use the ``-m`` command-line format to launch an installed module.
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Resolving the path of *executable* (or the first item of *args*) is
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platform dependent. For POSIX, see :meth:`os.execvpe`, and note that
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when resolving or searching for the executable path, *cwd* overrides the
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current working directory and *env* can override the ``PATH``
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environment variable. For Windows, see the documentation of the
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``lpApplicationName`` and ``lpCommandLine`` parameters of WinAPI
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``CreateProcess``, and note that when resolving or searching for the
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executable path with ``shell=False``, *cwd* does not override the
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current working directory and *env* cannot override the ``PATH``
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environment variable. Using a full path avoids all of these variations.
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An example of passing some arguments to an external program
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as a sequence is::
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Popen(["/usr/bin/git", "commit", "-m", "Fixes a bug."])
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On POSIX, 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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It may not be obvious how to break a shell command into a sequence of arguments,
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especially in complex cases. :meth:`shlex.split` can illustrate how to
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determine the correct tokenization for *args*::
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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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.. versionchanged:: 3.6
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*args* parameter accepts a :term:`path-like object` if *shell* is
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``False`` and a sequence containing path-like objects on POSIX.
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.. versionchanged:: 3.8
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*args* parameter accepts a :term:`path-like object` if *shell* is
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``False`` and a sequence containing bytes and path-like objects
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on Windows.
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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 POSIX 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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.. note::
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Read the `Security Considerations`_ section before using ``shell=True``.
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*bufsize* will be supplied as the corresponding argument to the
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:func:`open` function when creating the stdin/stdout/stderr pipe
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file objects:
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- ``0`` means unbuffered (read and write are one
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system call and can return short)
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- ``1`` means line buffered
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(only usable if ``text=True`` or ``universal_newlines=True``)
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- any other positive value means use a buffer of approximately that
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size
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- negative bufsize (the default) means the system default of
|
|
io.DEFAULT_BUFFER_SIZE will be used.
|
|
|
|
.. versionchanged:: 3.3.1
|
|
*bufsize* now defaults to -1 to enable buffering by default to match the
|
|
behavior that most code expects. In versions prior to Python 3.2.4 and
|
|
3.3.1 it incorrectly defaulted to ``0`` which was unbuffered
|
|
and allowed short reads. This was unintentional and did not match the
|
|
behavior of Python 2 as most code expected.
|
|
|
|
The *executable* argument specifies a replacement program to execute. It
|
|
is very seldom needed. When ``shell=False``, *executable* replaces the
|
|
program to execute specified by *args*. However, the original *args* is
|
|
still passed to the program. Most programs treat the program specified
|
|
by *args* as the command name, which can then be different from the program
|
|
actually executed. On POSIX, the *args* name
|
|
becomes the display name for the executable in utilities such as
|
|
:program:`ps`. If ``shell=True``, on POSIX the *executable* argument
|
|
specifies a replacement shell for the default :file:`/bin/sh`.
|
|
|
|
.. versionchanged:: 3.6
|
|
*executable* parameter accepts a :term:`path-like object` on POSIX.
|
|
|
|
.. versionchanged:: 3.8
|
|
*executable* parameter accepts a bytes and :term:`path-like object`
|
|
on Windows.
|
|
|
|
.. versionchanged:: 3.12
|
|
|
|
Changed Windows shell search order for ``shell=True``. The current
|
|
directory and ``%PATH%`` are replaced with ``%COMSPEC%`` and
|
|
``%SystemRoot%\System32\cmd.exe``. As a result, dropping a
|
|
malicious program named ``cmd.exe`` into a current directory no
|
|
longer works.
|
|
|
|
*stdin*, *stdout* and *stderr* specify the executed program's standard input,
|
|
standard output and standard error file handles, respectively. Valid values
|
|
are ``None``, :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a
|
|
positive integer), and an existing :term:`file object` with a valid file
|
|
descriptor. With the default settings of ``None``, no redirection will
|
|
occur. :data:`PIPE` indicates that a new pipe to the child should be
|
|
created. :data:`DEVNULL` indicates that the special file :data:`os.devnull`
|
|
will be used. Additionally, *stderr* can be :data:`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.
|
|
(POSIX only)
|
|
|
|
.. warning::
|
|
|
|
The *preexec_fn* parameter is NOT SAFE to use in the presence of threads
|
|
in your application. The child process could deadlock before exec is
|
|
called.
|
|
|
|
.. note::
|
|
|
|
If you need to modify the environment for the child use the *env*
|
|
parameter rather than doing it in a *preexec_fn*.
|
|
The *start_new_session* and *process_group* parameters should take the place of
|
|
code using *preexec_fn* to call :func:`os.setsid` or :func:`os.setpgid` in the child.
|
|
|
|
.. versionchanged:: 3.8
|
|
|
|
The *preexec_fn* parameter is no longer supported in subinterpreters.
|
|
The use of the parameter in a subinterpreter raises
|
|
:exc:`RuntimeError`. The new restriction may affect applications that
|
|
are deployed in mod_wsgi, uWSGI, and other embedded environments.
|
|
|
|
If *close_fds* is true, all file descriptors except ``0``, ``1`` and
|
|
``2`` will be closed before the child process is executed. Otherwise
|
|
when *close_fds* is false, file descriptors obey their inheritable flag
|
|
as described in :ref:`fd_inheritance`.
|
|
|
|
On Windows, if *close_fds* is true then no handles will be inherited by the
|
|
child process unless explicitly passed in the ``handle_list`` element of
|
|
:attr:`STARTUPINFO.lpAttributeList`, or by standard handle redirection.
|
|
|
|
.. versionchanged:: 3.2
|
|
The default for *close_fds* was changed from :const:`False` to
|
|
what is described above.
|
|
|
|
.. versionchanged:: 3.7
|
|
On Windows the default for *close_fds* was changed from :const:`False` to
|
|
:const:`True` when redirecting the standard handles. It's now possible to
|
|
set *close_fds* to :const:`True` when redirecting the standard handles.
|
|
|
|
*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`. (POSIX only)
|
|
|
|
.. versionchanged:: 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. *cwd* can be a string, bytes or
|
|
:term:`path-like <path-like object>` object. On POSIX, the function
|
|
looks for *executable* (or for the first item in *args*) relative to *cwd*
|
|
if the executable path is a relative path.
|
|
|
|
.. versionchanged:: 3.6
|
|
*cwd* parameter accepts a :term:`path-like object` on POSIX.
|
|
|
|
.. versionchanged:: 3.7
|
|
*cwd* parameter accepts a :term:`path-like object` on Windows.
|
|
|
|
.. versionchanged:: 3.8
|
|
*cwd* parameter accepts a bytes object on Windows.
|
|
|
|
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.
|
|
(POSIX 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.
|
|
|
|
.. availability:: POSIX
|
|
.. versionchanged:: 3.2
|
|
*start_new_session* was added.
|
|
|
|
If *process_group* is a non-negative integer, the ``setpgid(0, value)`` system call will
|
|
be made in the child process prior to the execution of the subprocess.
|
|
|
|
.. availability:: POSIX
|
|
.. versionchanged:: 3.11
|
|
*process_group* was added.
|
|
|
|
If *group* is not ``None``, the setregid() system call will be made in the
|
|
child process prior to the execution of the subprocess. If the provided
|
|
value is a string, it will be looked up via :func:`grp.getgrnam()` and
|
|
the value in ``gr_gid`` will be used. If the value is an integer, it
|
|
will be passed verbatim. (POSIX only)
|
|
|
|
.. availability:: POSIX
|
|
.. versionadded:: 3.9
|
|
|
|
If *extra_groups* is not ``None``, the setgroups() system call will be
|
|
made in the child process prior to the execution of the subprocess.
|
|
Strings provided in *extra_groups* will be looked up via
|
|
:func:`grp.getgrnam()` and the values in ``gr_gid`` will be used.
|
|
Integer values will be passed verbatim. (POSIX only)
|
|
|
|
.. availability:: POSIX
|
|
.. versionadded:: 3.9
|
|
|
|
If *user* is not ``None``, the setreuid() system call will be made in the
|
|
child process prior to the execution of the subprocess. If the provided
|
|
value is a string, it will be looked up via :func:`pwd.getpwnam()` and
|
|
the value in ``pw_uid`` will be used. If the value is an integer, it will
|
|
be passed verbatim. (POSIX only)
|
|
|
|
.. availability:: POSIX
|
|
.. versionadded:: 3.9
|
|
|
|
If *umask* is not negative, the umask() system call will be made in the
|
|
child process prior to the execution of the subprocess.
|
|
|
|
.. availability:: POSIX
|
|
.. versionadded:: 3.9
|
|
|
|
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. This mapping can be
|
|
str to str on any platform or bytes to bytes on POSIX platforms much like
|
|
:data:`os.environ` or :data:`os.environb`.
|
|
|
|
.. 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: https://en.wikipedia.org/wiki/Side-by-Side_Assembly
|
|
|
|
If *encoding* or *errors* are specified, or *text* is true, the file objects
|
|
*stdin*, *stdout* and *stderr* are opened in text mode with the specified
|
|
*encoding* and *errors*, as described above in :ref:`frequently-used-arguments`.
|
|
The *universal_newlines* argument is equivalent to *text* and is provided
|
|
for backwards compatibility. By default, file objects are opened in binary mode.
|
|
|
|
.. versionadded:: 3.6
|
|
*encoding* and *errors* were added.
|
|
|
|
.. versionadded:: 3.7
|
|
*text* was added as a more readable alias for *universal_newlines*.
|
|
|
|
If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is
|
|
passed to the underlying ``CreateProcess`` function.
|
|
*creationflags*, if given, can be one or more of the following flags:
|
|
|
|
* :data:`CREATE_NEW_CONSOLE`
|
|
* :data:`CREATE_NEW_PROCESS_GROUP`
|
|
* :data:`ABOVE_NORMAL_PRIORITY_CLASS`
|
|
* :data:`BELOW_NORMAL_PRIORITY_CLASS`
|
|
* :data:`HIGH_PRIORITY_CLASS`
|
|
* :data:`IDLE_PRIORITY_CLASS`
|
|
* :data:`NORMAL_PRIORITY_CLASS`
|
|
* :data:`REALTIME_PRIORITY_CLASS`
|
|
* :data:`CREATE_NO_WINDOW`
|
|
* :data:`DETACHED_PROCESS`
|
|
* :data:`CREATE_DEFAULT_ERROR_MODE`
|
|
* :data:`CREATE_BREAKAWAY_FROM_JOB`
|
|
|
|
*pipesize* can be used to change the size of the pipe when
|
|
:data:`PIPE` is used for *stdin*, *stdout* or *stderr*. The size of the pipe
|
|
is only changed on platforms that support this (only Linux at this time of
|
|
writing). Other platforms will ignore this parameter.
|
|
|
|
.. versionadded:: 3.10
|
|
The ``pipesize`` parameter was added.
|
|
|
|
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())
|
|
|
|
.. audit-event:: subprocess.Popen executable,args,cwd,env subprocess.Popen
|
|
|
|
Popen and the other functions in this module that use it raise an
|
|
:ref:`auditing event <auditing>` ``subprocess.Popen`` with arguments
|
|
``executable``, ``args``, ``cwd``, and ``env``. The value for ``args``
|
|
may be a single string or a list of strings, depending on platform.
|
|
|
|
.. versionchanged:: 3.2
|
|
Added context manager support.
|
|
|
|
.. versionchanged:: 3.6
|
|
Popen destructor now emits a :exc:`ResourceWarning` warning if the child
|
|
process is still running.
|
|
|
|
.. versionchanged:: 3.8
|
|
Popen can use :func:`os.posix_spawn` in some cases for better
|
|
performance. On Windows Subsystem for Linux and QEMU User Emulation,
|
|
Popen constructor using :func:`os.posix_spawn` no longer raise an
|
|
exception on errors like missing program, but the child process fails
|
|
with a non-zero :attr:`~Popen.returncode`.
|
|
|
|
|
|
Exceptions
|
|
^^^^^^^^^^
|
|
|
|
Exceptions raised in the child process, before the new program has started to
|
|
execute, will be re-raised in the parent.
|
|
|
|
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. Note that, when ``shell=True``, :exc:`OSError`
|
|
will be raised by the child only if the selected shell itself was not found.
|
|
To determine if the shell failed to find the requested application, it is
|
|
necessary to check the return code or output from the subprocess.
|
|
|
|
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:`run` 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.
|
|
|
|
.. _subprocess-security:
|
|
|
|
Security Considerations
|
|
-----------------------
|
|
|
|
Unlike some other popen functions, this implementation will never
|
|
implicitly call a system shell. This means that all characters,
|
|
including shell metacharacters, can safely be passed to child processes.
|
|
If the shell is invoked explicitly, via ``shell=True``, it is the application's
|
|
responsibility to ensure that all whitespace and metacharacters are
|
|
quoted appropriately to avoid
|
|
`shell injection <https://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_
|
|
vulnerabilities. On :ref:`some platforms <shlex-quote-warning>`, it is possible
|
|
to use :func:`shlex.quote` for this escaping.
|
|
|
|
|
|
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:`~Popen.returncode` attribute. Otherwise, returns ``None``.
|
|
|
|
|
|
.. method:: Popen.wait(timeout=None)
|
|
|
|
Wait for child process to terminate. Set and return
|
|
:attr:`~Popen.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.
|
|
|
|
.. note::
|
|
|
|
This will deadlock when using ``stdout=PIPE`` 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:`Popen.communicate` when using pipes to avoid that.
|
|
|
|
.. note::
|
|
|
|
When the ``timeout`` parameter is not ``None``, then (on POSIX) the
|
|
function is implemented using a busy loop (non-blocking call and short
|
|
sleeps). Use the :mod:`asyncio` module for an asynchronous wait: see
|
|
:class:`asyncio.create_subprocess_exec`.
|
|
|
|
.. 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 and set the
|
|
:attr:`~Popen.returncode` attribute. 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. If streams were opened in text mode, *input* must be a string.
|
|
Otherwise, it must be bytes.
|
|
|
|
:meth:`communicate` returns a tuple ``(stdout_data, stderr_data)``.
|
|
The data will be strings if streams were opened in text mode; otherwise,
|
|
bytes.
|
|
|
|
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.
|
|
|
|
Do nothing if the process completed.
|
|
|
|
.. 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 set by the class for you to access.
|
|
Reassigning them to new values is unsupported:
|
|
|
|
.. attribute:: Popen.args
|
|
|
|
The *args* argument as it was passed to :class:`Popen` -- a
|
|
sequence of program arguments or else a single string.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
.. attribute:: Popen.stdin
|
|
|
|
If the *stdin* argument was :data:`PIPE`, this attribute is a writeable
|
|
stream object as returned by :func:`open`. If the *encoding* or *errors*
|
|
arguments were specified or the *text* or *universal_newlines* argument
|
|
was ``True``, the stream is a text stream, otherwise it is a byte stream.
|
|
If the *stdin* argument was not :data:`PIPE`, this attribute is ``None``.
|
|
|
|
|
|
.. attribute:: Popen.stdout
|
|
|
|
If the *stdout* argument was :data:`PIPE`, this attribute is a readable
|
|
stream object as returned by :func:`open`. Reading from the stream provides
|
|
output from the child process. If the *encoding* or *errors* arguments were
|
|
specified or the *text* or *universal_newlines* argument was ``True``, the
|
|
stream is a text stream, otherwise it is a byte stream. If the *stdout*
|
|
argument was not :data:`PIPE`, this attribute is ``None``.
|
|
|
|
|
|
.. attribute:: Popen.stderr
|
|
|
|
If the *stderr* argument was :data:`PIPE`, this attribute is a readable
|
|
stream object as returned by :func:`open`. Reading from the stream provides
|
|
error output from the child process. If the *encoding* or *errors* arguments
|
|
were specified or the *text* or *universal_newlines* argument was ``True``, the
|
|
stream is a text stream, otherwise it is a byte stream. If the *stderr* argument
|
|
was not :data:`PIPE`, this attribute is ``None``.
|
|
|
|
.. 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.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. Initially ``None``, :attr:`returncode` is set by
|
|
a call to the :meth:`poll`, :meth:`wait`, or :meth:`communicate` methods
|
|
if they detect that the process has terminated.
|
|
|
|
A ``None`` value indicates that the process hadn't yet terminated at the
|
|
time of the last method call.
|
|
|
|
A negative value ``-N`` indicates that the child was terminated by signal
|
|
``N`` (POSIX only).
|
|
|
|
|
|
Windows Popen Helpers
|
|
---------------------
|
|
|
|
The :class:`STARTUPINFO` class and following constants are only available
|
|
on Windows.
|
|
|
|
.. class:: STARTUPINFO(*, dwFlags=0, hStdInput=None, hStdOutput=None, \
|
|
hStdError=None, wShowWindow=0, lpAttributeList=None)
|
|
|
|
Partial support of the Windows
|
|
`STARTUPINFO <https://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx>`__
|
|
structure is used for :class:`Popen` creation. The following attributes can
|
|
be set by passing them as keyword-only arguments.
|
|
|
|
.. versionchanged:: 3.7
|
|
Keyword-only argument support was added.
|
|
|
|
.. 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 <https://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``.
|
|
|
|
.. attribute:: lpAttributeList
|
|
|
|
A dictionary of additional attributes for process creation as given in
|
|
``STARTUPINFOEX``, see
|
|
`UpdateProcThreadAttribute <https://msdn.microsoft.com/en-us/library/windows/desktop/ms686880(v=vs.85).aspx>`__.
|
|
|
|
Supported attributes:
|
|
|
|
**handle_list**
|
|
Sequence of handles that will be inherited. *close_fds* must be true if
|
|
non-empty.
|
|
|
|
The handles must be temporarily made inheritable by
|
|
:func:`os.set_handle_inheritable` when passed to the :class:`Popen`
|
|
constructor, else :class:`OSError` will be raised with Windows error
|
|
``ERROR_INVALID_PARAMETER`` (87).
|
|
|
|
.. warning::
|
|
|
|
In a multithreaded process, use caution to avoid leaking handles
|
|
that are marked inheritable when combining this feature with
|
|
concurrent calls to other process creation functions that inherit
|
|
all handles such as :func:`os.system`. This also applies to
|
|
standard handle redirection, which temporarily creates inheritable
|
|
handles.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
Windows 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).
|
|
|
|
.. 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.
|
|
|
|
.. data:: ABOVE_NORMAL_PRIORITY_CLASS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will have an above average priority.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: BELOW_NORMAL_PRIORITY_CLASS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will have a below average priority.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: HIGH_PRIORITY_CLASS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will have a high priority.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: IDLE_PRIORITY_CLASS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will have an idle (lowest) priority.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: NORMAL_PRIORITY_CLASS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will have an normal priority. (default)
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: REALTIME_PRIORITY_CLASS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will have realtime priority.
|
|
You should almost never use REALTIME_PRIORITY_CLASS, because this interrupts
|
|
system threads that manage mouse input, keyboard input, and background disk
|
|
flushing. This class can be appropriate for applications that "talk" directly
|
|
to hardware or that perform brief tasks that should have limited interruptions.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: CREATE_NO_WINDOW
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will not create a window.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: DETACHED_PROCESS
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
will not inherit its parent's console.
|
|
This value cannot be used with CREATE_NEW_CONSOLE.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: CREATE_DEFAULT_ERROR_MODE
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
does not inherit the error mode of the calling process. Instead, the new
|
|
process gets the default error mode.
|
|
This feature is particularly useful for multithreaded shell applications
|
|
that run with hard errors disabled.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. data:: CREATE_BREAKAWAY_FROM_JOB
|
|
|
|
A :class:`Popen` ``creationflags`` parameter to specify that a new process
|
|
is not associated with the job.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. _call-function-trio:
|
|
|
|
Older high-level API
|
|
--------------------
|
|
|
|
Prior to Python 3.5, these three functions comprised the high level API to
|
|
subprocess. You can now use :func:`run` in many cases, but lots of existing code
|
|
calls these functions.
|
|
|
|
.. function:: call(args, *, stdin=None, stdout=None, stderr=None, \
|
|
shell=False, cwd=None, timeout=None, **other_popen_kwargs)
|
|
|
|
Run the command described by *args*. Wait for command to complete, then
|
|
return the :attr:`~Popen.returncode` attribute.
|
|
|
|
Code needing to capture stdout or stderr should use :func:`run` instead::
|
|
|
|
run(...).returncode
|
|
|
|
To suppress stdout or stderr, supply a value of :data:`DEVNULL`.
|
|
|
|
The arguments shown above are merely some common ones.
|
|
The full function signature is the
|
|
same as that of the :class:`Popen` constructor - this function passes all
|
|
supplied arguments other than *timeout* directly through to that interface.
|
|
|
|
.. note::
|
|
|
|
Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this
|
|
function. The child process will block if it generates enough
|
|
output to a pipe to fill up the OS pipe buffer as the pipes are
|
|
not being read from.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
.. versionchanged:: 3.12
|
|
|
|
Changed Windows shell search order for ``shell=True``. The current
|
|
directory and ``%PATH%`` are replaced with ``%COMSPEC%`` and
|
|
``%SystemRoot%\System32\cmd.exe``. As a result, dropping a
|
|
malicious program named ``cmd.exe`` into a current directory no
|
|
longer works.
|
|
|
|
.. function:: check_call(args, *, stdin=None, stdout=None, stderr=None, \
|
|
shell=False, cwd=None, timeout=None, \
|
|
**other_popen_kwargs)
|
|
|
|
Run command with arguments. Wait for command to complete. If the return
|
|
code was zero then return, otherwise raise :exc:`CalledProcessError`. The
|
|
:exc:`CalledProcessError` object will have the return code in the
|
|
:attr:`~CalledProcessError.returncode` attribute.
|
|
If :func:`check_call` was unable to start the process it will propagate the exception
|
|
that was raised.
|
|
|
|
Code needing to capture stdout or stderr should use :func:`run` instead::
|
|
|
|
run(..., check=True)
|
|
|
|
To suppress stdout or stderr, supply a value of :data:`DEVNULL`.
|
|
|
|
The arguments shown above are merely some common ones.
|
|
The full function signature is the
|
|
same as that of the :class:`Popen` constructor - this function passes all
|
|
supplied arguments other than *timeout* directly through to that interface.
|
|
|
|
.. note::
|
|
|
|
Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this
|
|
function. The child process will block if it generates enough
|
|
output to a pipe to fill up the OS pipe buffer as the pipes are
|
|
not being read from.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
.. versionchanged:: 3.12
|
|
|
|
Changed Windows shell search order for ``shell=True``. The current
|
|
directory and ``%PATH%`` are replaced with ``%COMSPEC%`` and
|
|
``%SystemRoot%\System32\cmd.exe``. As a result, dropping a
|
|
malicious program named ``cmd.exe`` into a current directory no
|
|
longer works.
|
|
|
|
|
|
.. function:: check_output(args, *, stdin=None, stderr=None, shell=False, \
|
|
cwd=None, encoding=None, errors=None, \
|
|
universal_newlines=None, timeout=None, text=None, \
|
|
**other_popen_kwargs)
|
|
|
|
Run command with arguments and return its output.
|
|
|
|
If the return code was non-zero it raises a :exc:`CalledProcessError`. The
|
|
:exc:`CalledProcessError` object will have the return code in the
|
|
:attr:`~CalledProcessError.returncode` attribute and any output in the
|
|
:attr:`~CalledProcessError.output` attribute.
|
|
|
|
This is equivalent to::
|
|
|
|
run(..., check=True, stdout=PIPE).stdout
|
|
|
|
The arguments shown above are merely some common ones.
|
|
The full function signature is largely the same as that of :func:`run` -
|
|
most arguments are passed directly through to that interface.
|
|
One API deviation from :func:`run` behavior exists: passing ``input=None``
|
|
will behave the same as ``input=b''`` (or ``input=''``, depending on other
|
|
arguments) rather than using the parent's standard input file handle.
|
|
|
|
By default, this function will return the data as encoded bytes. The actual
|
|
encoding of the output data may depend on the command being invoked, so the
|
|
decoding to text will often need to be handled at the application level.
|
|
|
|
This behaviour may be overridden by setting *text*, *encoding*, *errors*,
|
|
or *universal_newlines* to ``True`` as described in
|
|
:ref:`frequently-used-arguments` and :func:`run`.
|
|
|
|
To also capture standard error in the result, use
|
|
``stderr=subprocess.STDOUT``::
|
|
|
|
>>> subprocess.check_output(
|
|
... "ls non_existent_file; exit 0",
|
|
... stderr=subprocess.STDOUT,
|
|
... shell=True)
|
|
'ls: non_existent_file: No such file or directory\n'
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
.. versionchanged:: 3.4
|
|
Support for the *input* keyword argument was added.
|
|
|
|
.. versionchanged:: 3.6
|
|
*encoding* and *errors* were added. See :func:`run` for details.
|
|
|
|
.. versionadded:: 3.7
|
|
*text* was added as a more readable alias for *universal_newlines*.
|
|
|
|
.. versionchanged:: 3.12
|
|
|
|
Changed Windows shell search order for ``shell=True``. The current
|
|
directory and ``%PATH%`` are replaced with ``%COMSPEC%`` and
|
|
``%SystemRoot%\System32\cmd.exe``. As a result, dropping a
|
|
malicious program named ``cmd.exe`` into a current directory no
|
|
longer works.
|
|
|
|
|
|
.. _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
|
|
:attr:`~CalledProcessError.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 :program:`/bin/sh` shell command substitution
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
.. code-block:: bash
|
|
|
|
output=$(mycmd myarg)
|
|
|
|
becomes::
|
|
|
|
output = check_output(["mycmd", "myarg"])
|
|
|
|
Replacing shell pipeline
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
.. code-block:: bash
|
|
|
|
output=$(dmesg | grep hda)
|
|
|
|
becomes::
|
|
|
|
p1 = Popen(["dmesg"], stdout=PIPE)
|
|
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
|
|
p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits.
|
|
output = p2.communicate()[0]
|
|
|
|
The ``p1.stdout.close()`` call after starting the p2 is important in order for
|
|
p1 to receive a SIGPIPE if p2 exits before p1.
|
|
|
|
Alternatively, for trusted input, the shell's own pipeline support may still
|
|
be used directly:
|
|
|
|
.. code-block:: bash
|
|
|
|
output=$(dmesg | grep hda)
|
|
|
|
becomes::
|
|
|
|
output = check_output("dmesg | grep hda", shell=True)
|
|
|
|
|
|
Replacing :func:`os.system`
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
sts = os.system("mycmd" + " myarg")
|
|
# becomes
|
|
retcode = call("mycmd" + " myarg", shell=True)
|
|
|
|
Notes:
|
|
|
|
* Calling the program through the shell is usually not required.
|
|
* The :func:`call` return value is encoded differently to that of
|
|
:func:`os.system`.
|
|
|
|
* The :func:`os.system` function ignores SIGINT and SIGQUIT signals while
|
|
the command is running, but the caller must do this separately when
|
|
using the :mod:`subprocess` module.
|
|
|
|
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, 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, *, encoding=None, errors=None)
|
|
|
|
Return ``(exitcode, output)`` of executing *cmd* in a shell.
|
|
|
|
Execute the string *cmd* in a shell with :meth:`Popen.check_output` and
|
|
return a 2-tuple ``(exitcode, output)``.
|
|
*encoding* and *errors* are used to decode output;
|
|
see the notes on :ref:`frequently-used-arguments` for more details.
|
|
|
|
A trailing newline is stripped from the output.
|
|
The exit code for the command can be interpreted as the return code
|
|
of subprocess. Example::
|
|
|
|
>>> subprocess.getstatusoutput('ls /bin/ls')
|
|
(0, '/bin/ls')
|
|
>>> subprocess.getstatusoutput('cat /bin/junk')
|
|
(1, 'cat: /bin/junk: No such file or directory')
|
|
>>> subprocess.getstatusoutput('/bin/junk')
|
|
(127, 'sh: /bin/junk: not found')
|
|
>>> subprocess.getstatusoutput('/bin/kill $$')
|
|
(-15, '')
|
|
|
|
.. availability:: Unix, Windows.
|
|
|
|
.. versionchanged:: 3.3.4
|
|
Windows support was added.
|
|
|
|
The function now returns (exitcode, output) instead of (status, output)
|
|
as it did in Python 3.3.3 and earlier. exitcode has the same value as
|
|
:attr:`~Popen.returncode`.
|
|
|
|
.. versionadded:: 3.11
|
|
Added *encoding* and *errors* arguments.
|
|
|
|
.. function:: getoutput(cmd, *, encoding=None, errors=None)
|
|
|
|
Return output (stdout and stderr) of executing *cmd* in a shell.
|
|
|
|
Like :func:`getstatusoutput`, except the exit code is ignored and the return
|
|
value is a string containing the command's output. Example::
|
|
|
|
>>> subprocess.getoutput('ls /bin/ls')
|
|
'/bin/ls'
|
|
|
|
.. availability:: Unix, Windows.
|
|
|
|
.. versionchanged:: 3.3.4
|
|
Windows support added
|
|
|
|
.. versionadded:: 3.11
|
|
Added *encoding* and *errors* arguments.
|
|
|
|
|
|
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.
|
|
|
|
|
|
.. _disable_vfork:
|
|
.. _disable_posix_spawn:
|
|
|
|
Disabling use of ``vfork()`` or ``posix_spawn()``
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
On Linux, :mod:`subprocess` defaults to using the ``vfork()`` system call
|
|
internally when it is safe to do so rather than ``fork()``. This greatly
|
|
improves performance.
|
|
|
|
If you ever encounter a presumed highly unusual situation where you need to
|
|
prevent ``vfork()`` from being used by Python, you can set the
|
|
:const:`subprocess._USE_VFORK` attribute to a false value.
|
|
|
|
::
|
|
|
|
subprocess._USE_VFORK = False # See CPython issue gh-NNNNNN.
|
|
|
|
Setting this has no impact on use of ``posix_spawn()`` which could use
|
|
``vfork()`` internally within its libc implementation. There is a similar
|
|
:const:`subprocess._USE_POSIX_SPAWN` attribute if you need to prevent use of
|
|
that.
|
|
|
|
::
|
|
|
|
subprocess._USE_POSIX_SPAWN = False # See CPython issue gh-NNNNNN.
|
|
|
|
It is safe to set these to false on any Python version. They will have no
|
|
effect on older versions when unsupported. Do not assume the attributes are
|
|
available to read. Despite their names, a true value does not indicate that the
|
|
corresponding function will be used, only that it may be.
|
|
|
|
Please file issues any time you have to use these private knobs with a way to
|
|
reproduce the issue you were seeing. Link to that issue from a comment in your
|
|
code.
|
|
|
|
.. versionadded:: 3.8 ``_USE_POSIX_SPAWN``
|
|
.. versionadded:: 3.11 ``_USE_VFORK``
|