1135 lines
41 KiB
ReStructuredText
1135 lines
41 KiB
ReStructuredText
:mod:`subprocess` --- Subprocess management
|
|
===========================================
|
|
|
|
.. module:: subprocess
|
|
:synopsis: Subprocess management.
|
|
.. moduleauthor:: Peter Åstrand <astrand@lysator.liu.se>
|
|
.. sectionauthor:: Peter Åstrand <astrand@lysator.liu.se>
|
|
|
|
|
|
The :mod:`subprocess` module allows you to spawn new processes, connect to their
|
|
input/output/error pipes, and obtain their return codes. This module intends to
|
|
replace several older modules and functions::
|
|
|
|
os.system
|
|
os.spawn*
|
|
|
|
Information about how the :mod:`subprocess` module can be used to replace these
|
|
modules and functions can be found in the following sections.
|
|
|
|
.. seealso::
|
|
|
|
:pep:`324` -- PEP proposing the subprocess module
|
|
|
|
|
|
Using the :mod:`subprocess` Module
|
|
----------------------------------
|
|
|
|
The recommended approach to invoking subprocesses is to use the following
|
|
convenience functions for all use cases they can handle. For more advanced
|
|
use cases, the underlying :class:`Popen` interface can be used directly.
|
|
|
|
|
|
.. function:: call(args, *, stdin=None, stdout=None, stderr=None, shell=False, timeout=None)
|
|
|
|
Run the command described by *args*. Wait for command to complete, then
|
|
return the :attr:`returncode` attribute.
|
|
|
|
The arguments shown above are merely the most common ones, described below
|
|
in :ref:`frequently-used-arguments` (hence the use of keyword-only notation
|
|
in the abbreviated signature). The full function signature is largely the
|
|
same as that of the :class:`Popen` constructor - this function passes all
|
|
supplied arguments other than *timeout* directly through to that interface.
|
|
|
|
The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout
|
|
expires, the child process will be killed and then waited for again. The
|
|
:exc:`TimeoutExpired` exception will be re-raised after the child process
|
|
has terminated.
|
|
|
|
Examples::
|
|
|
|
>>> subprocess.call(["ls", "-l"])
|
|
0
|
|
|
|
>>> subprocess.call("exit 1", shell=True)
|
|
1
|
|
|
|
.. 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.
|
|
|
|
|
|
.. function:: check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, timeout=None)
|
|
|
|
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.
|
|
|
|
The arguments shown above are merely the most common ones, described below
|
|
in :ref:`frequently-used-arguments` (hence the use of keyword-only notation
|
|
in the abbreviated signature). The full function signature is largely the
|
|
same as that of the :class:`Popen` constructor - this function passes all
|
|
supplied arguments other than *timeout* directly through to that interface.
|
|
|
|
The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout
|
|
expires, the child process will be killed and then waited for again. The
|
|
:exc:`TimeoutExpired` exception will be re-raised after the child process
|
|
has terminated.
|
|
|
|
Examples::
|
|
|
|
>>> subprocess.check_call(["ls", "-l"])
|
|
0
|
|
|
|
>>> subprocess.check_call("exit 1", shell=True)
|
|
Traceback (most recent call last):
|
|
...
|
|
subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1
|
|
|
|
.. 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.
|
|
|
|
|
|
.. function:: check_output(args, *, input=None, stdin=None, stderr=None, shell=False, universal_newlines=False, timeout=None)
|
|
|
|
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.
|
|
|
|
The arguments shown above are merely the most common ones, described below
|
|
in :ref:`frequently-used-arguments` (hence the use of keyword-only notation
|
|
in the abbreviated signature). The full function signature is largely the
|
|
same as that of the :class:`Popen` constructor - this functions passes all
|
|
supplied arguments other than *input* and *timeout* directly through to
|
|
that interface. In addition, *stdout* is not permitted as an argument, as
|
|
it is used internally to collect the output from the subprocess.
|
|
|
|
The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout
|
|
expires, the child process will be killed and then waited for again. The
|
|
:exc:`TimeoutExpired` exception will be re-raised after the child process
|
|
has terminated.
|
|
|
|
The *input* argument is passed to :meth:`Popen.communicate` and thus to the
|
|
subprocess's stdin. If used it must be a byte sequence, or a string if
|
|
``universal_newlines=True``. When used, the internal :class:`Popen` object
|
|
is automatically created with ``stdin=PIPE``, and the *stdin* argument may
|
|
not be used as well.
|
|
|
|
Examples::
|
|
|
|
>>> subprocess.check_output(["echo", "Hello World!"])
|
|
b'Hello World!\n'
|
|
|
|
>>> subprocess.check_output(["echo", "Hello World!"], universal_newlines=True)
|
|
'Hello World!\n'
|
|
|
|
>>> subprocess.check_output(["sed", "-e", "s/foo/bar/"],
|
|
... input=b"when in the course of fooman events\n")
|
|
b'when in the course of barman events\n'
|
|
|
|
>>> subprocess.check_output("exit 1", shell=True)
|
|
Traceback (most recent call last):
|
|
...
|
|
subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1
|
|
|
|
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 *universal_newlines* to
|
|
``True`` as described below in :ref:`frequently-used-arguments`.
|
|
|
|
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'
|
|
|
|
.. 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.
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
.. versionchanged:: 3.4
|
|
*input* was added.
|
|
|
|
.. data:: DEVNULL
|
|
|
|
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
|
|
to :class:`Popen` and indicates that the special file :data:`os.devnull`
|
|
will be used.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. data:: PIPE
|
|
|
|
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
|
|
to :class:`Popen` and indicates that a pipe to the standard stream should be
|
|
opened. Most useful with :meth:`Popen.communicate`.
|
|
|
|
|
|
.. data:: STDOUT
|
|
|
|
Special value that can be used as the *stderr* argument to :class:`Popen` and
|
|
indicates that standard error should go into the same handle as standard
|
|
output.
|
|
|
|
|
|
.. exception:: SubprocessError
|
|
|
|
Base class for all other exceptions from this module.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. exception:: TimeoutExpired
|
|
|
|
Subclass of :exc:`SubprocessError`, raised when a timeout expires
|
|
while waiting for a child process.
|
|
|
|
.. attribute:: cmd
|
|
|
|
Command that was used to spawn the child process.
|
|
|
|
.. attribute:: timeout
|
|
|
|
Timeout in seconds.
|
|
|
|
.. attribute:: output
|
|
|
|
Output of the child process if this exception is raised by
|
|
:func:`check_output`. Otherwise, ``None``.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. exception:: CalledProcessError
|
|
|
|
Subclass of :exc:`SubprocessError`, raised when a process run by
|
|
:func:`check_call` or :func:`check_output` returns a non-zero exit status.
|
|
|
|
.. attribute:: returncode
|
|
|
|
Exit status of the child process.
|
|
|
|
.. attribute:: cmd
|
|
|
|
Command that was used to spawn the child process.
|
|
|
|
.. attribute:: output
|
|
|
|
Output of the child process if this exception is raised by
|
|
:func:`check_output`. Otherwise, ``None``.
|
|
|
|
|
|
|
|
.. _frequently-used-arguments:
|
|
|
|
Frequently Used Arguments
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
To support a wide variety of use cases, the :class:`Popen` constructor (and
|
|
the convenience functions) accept a large number of optional arguments. For
|
|
most typical use cases, many of these arguments can be safely left at their
|
|
default values. The arguments that are most commonly needed are:
|
|
|
|
*args* is required for all calls and should be a string, or a sequence of
|
|
program arguments. Providing a sequence of arguments is generally
|
|
preferred, as it allows the module to take care of any required escaping
|
|
and quoting of arguments (e.g. to permit spaces in file names). If passing
|
|
a single string, either *shell* must be :const:`True` (see below) or else
|
|
the string must simply name the program to be executed without specifying
|
|
any arguments.
|
|
|
|
*stdin*, *stdout* and *stderr* specify the executed program's standard input,
|
|
standard output and standard error file handles, respectively. Valid values
|
|
are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive
|
|
integer), an existing file object, and ``None``. :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. With the default
|
|
settings of ``None``, no redirection will occur; the child's file handles
|
|
will be inherited from the parent. Additionally, *stderr* can be
|
|
:data:`STDOUT`, which indicates that the stderr data from the child
|
|
process should be captured into the same file handle as for *stdout*.
|
|
|
|
.. index::
|
|
single: universal newlines; subprocess module
|
|
|
|
If *universal_newlines* is ``False`` the file objects *stdin*, *stdout* and
|
|
*stderr* will be opened as binary streams, and no line ending conversion is
|
|
done.
|
|
|
|
If *universal_newlines* is ``True``, these file objects
|
|
will be opened as text streams in :term:`universal newlines` mode
|
|
using the encoding returned by :func:`locale.getpreferredencoding(False)
|
|
<locale.getpreferredencoding>`. For *stdin*, line ending characters
|
|
``'\n'`` in the input will be converted to the default line separator
|
|
:data:`os.linesep`. For *stdout* and *stderr*, all line endings in the
|
|
output will be converted to ``'\n'``. For more information see the
|
|
documentation of the :class:`io.TextIOWrapper` class when the *newline*
|
|
argument to its constructor is ``None``.
|
|
|
|
.. note::
|
|
|
|
The newlines attribute of the file objects :attr:`Popen.stdin`,
|
|
:attr:`Popen.stdout` and :attr:`Popen.stderr` are not updated by
|
|
the :meth:`Popen.communicate` method.
|
|
|
|
If *shell* is ``True``, the specified command will be executed through
|
|
the shell. This can be useful if you are using Python primarily for the
|
|
enhanced control flow it offers over most system shells and still want
|
|
convenient access to other shell features such as shell pipes, filename
|
|
wildcards, environment variable expansion, and expansion of ``~`` to a
|
|
user's home directory. However, note that Python itself offers
|
|
implementations of many shell-like features (in particular, :mod:`glob`,
|
|
:mod:`fnmatch`, :func:`os.walk`, :func:`os.path.expandvars`,
|
|
:func:`os.path.expanduser`, and :mod:`shutil`).
|
|
|
|
.. versionchanged:: 3.3
|
|
When *universal_newlines* is ``True``, the class uses the encoding
|
|
:func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`
|
|
instead of ``locale.getpreferredencoding()``. See the
|
|
:class:`io.TextIOWrapper` class for more information on this change.
|
|
|
|
.. note::
|
|
|
|
Read the `Security Considerations`_ section before using ``shell=True``.
|
|
|
|
These options, along with all of the other options, are described in more
|
|
detail in the :class:`Popen` constructor documentation.
|
|
|
|
|
|
Popen Constructor
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
The underlying process creation and management in this module is handled by
|
|
the :class:`Popen` class. It offers a lot of flexibility so that developers
|
|
are able to handle the less common cases not covered by the convenience
|
|
functions.
|
|
|
|
|
|
.. class:: Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, \
|
|
stderr=None, preexec_fn=None, close_fds=True, shell=False, \
|
|
cwd=None, env=None, universal_newlines=False, \
|
|
startupinfo=None, creationflags=0, restore_signals=True, \
|
|
start_new_session=False, pass_fds=())
|
|
|
|
Execute a child program in a new process. On POSIX, the class uses
|
|
:meth:`os.execvp`-like behavior to execute the child program. On Windows,
|
|
the class uses the Windows ``CreateProcess()`` function. The arguments to
|
|
:class:`Popen` are as follows.
|
|
|
|
*args* should be a sequence of program arguments or else a single string.
|
|
By default, the program to execute is the first item in *args* if *args* is
|
|
a sequence. If *args* is a string, the interpretation is
|
|
platform-dependent and described below. See the *shell* and *executable*
|
|
arguments for additional differences from the default behavior. Unless
|
|
otherwise stated, it is recommended to pass *args* as a sequence.
|
|
|
|
On POSIX, if *args* is a string, the string is interpreted as the name or
|
|
path of the program to execute. However, this can only be done if not
|
|
passing arguments to the program.
|
|
|
|
.. note::
|
|
|
|
:meth:`shlex.split` can be useful when determining the correct
|
|
tokenization for *args*, especially in complex cases::
|
|
|
|
>>> import shlex, subprocess
|
|
>>> command_line = input()
|
|
/bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'"
|
|
>>> args = shlex.split(command_line)
|
|
>>> print(args)
|
|
['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"]
|
|
>>> p = subprocess.Popen(args) # Success!
|
|
|
|
Note in particular that options (such as *-input*) and arguments (such
|
|
as *eggs.txt*) that are separated by whitespace in the shell go in separate
|
|
list elements, while arguments that need quoting or backslash escaping when
|
|
used in the shell (such as filenames containing spaces or the *echo* command
|
|
shown above) are single list elements.
|
|
|
|
On Windows, if *args* is a sequence, it will be converted to a string in a
|
|
manner described in :ref:`converting-argument-sequence`. This is because
|
|
the underlying ``CreateProcess()`` operates on strings.
|
|
|
|
The *shell* argument (which defaults to *False*) specifies whether to use
|
|
the shell as the program to execute. If *shell* is *True*, it is
|
|
recommended to pass *args* as a string rather than as a sequence.
|
|
|
|
On POSIX with ``shell=True``, the shell defaults to :file:`/bin/sh`. If
|
|
*args* is a string, the string specifies the command
|
|
to execute through the shell. This means that the string must be
|
|
formatted exactly as it would be when typed at the shell prompt. This
|
|
includes, for example, quoting or backslash escaping filenames with spaces in
|
|
them. If *args* is a sequence, the first item specifies the command string, and
|
|
any additional items will be treated as additional arguments to the shell
|
|
itself. That is to say, :class:`Popen` does the equivalent of::
|
|
|
|
Popen(['/bin/sh', '-c', args[0], args[1], ...])
|
|
|
|
On Windows with ``shell=True``, the :envvar:`COMSPEC` environment variable
|
|
specifies the default shell. The only time you need to specify
|
|
``shell=True`` on Windows is when the command you wish to execute is built
|
|
into the shell (e.g. :command:`dir` or :command:`copy`). You do not need
|
|
``shell=True`` to run a batch file or console-based executable.
|
|
|
|
.. note::
|
|
|
|
Read the `Security Considerations`_ section before using ``shell=True``.
|
|
|
|
*bufsize* will be supplied as the corresponding argument to the
|
|
:func:`open` function when creating the stdin/stdout/stderr pipe
|
|
file objects:
|
|
|
|
- :const:`0` means unbuffered (read and write are one
|
|
system call and can return short)
|
|
- :const:`1` means line buffered
|
|
(only usable if ``universal_newlines=True`` i.e., in a text mode)
|
|
- any other positive value means use a buffer of approximately that
|
|
size
|
|
- 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 :const:`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`.
|
|
|
|
*stdin*, *stdout* and *stderr* specify the executed program's standard input,
|
|
standard output and standard error file handles, respectively. Valid values
|
|
are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive
|
|
integer), an existing :term:`file object`, and ``None``. :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. With the
|
|
default settings of ``None``, no redirection will occur; the child's file
|
|
handles will be inherited from the parent. 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.
|
|
If you must use it, keep it trivial! Minimize the number of libraries
|
|
you call into.
|
|
|
|
.. 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* parameter can take the place of a previously
|
|
common use of *preexec_fn* to call os.setsid() in the child.
|
|
|
|
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. (POSIX only).
|
|
The default varies by platform: Always true on POSIX. 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`. (POSIX 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.
|
|
(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. (POSIX 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`, otherwise they are
|
|
opened as binary streams.
|
|
|
|
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 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 <http://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_
|
|
vulnerabilities.
|
|
|
|
When using ``shell=True``, the :func:`shlex.quote` function can be
|
|
used to properly escape whitespace and shell metacharacters in strings
|
|
that are going to be used to construct shell commands.
|
|
|
|
|
|
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.
|
|
|
|
|
|
.. 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::
|
|
|
|
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.
|
|
|
|
.. deprecated:: 3.4
|
|
|
|
Do not use the *endtime* parameter. It is was unintentionally
|
|
exposed in 3.3 but was left undocumented as it was intended to be
|
|
private for internal use. Use *timeout* instead.
|
|
|
|
.. 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)``.
|
|
The data will be bytes or, if *universal_newlines* was ``True``, strings.
|
|
|
|
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:
|
|
|
|
.. 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 *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 *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 *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, 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`` (POSIX 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).
|
|
|
|
.. 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
|
|
: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 /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 :meth:`Popen.check_output` and
|
|
return a 2-tuple ``(status, output)``. Universal newlines mode is used;
|
|
see the notes on :ref:`frequently-used-arguments` for more details.
|
|
|
|
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: POSIX & Windows
|
|
|
|
.. versionchanged:: 3.3.4
|
|
Windows support added
|
|
|
|
|
|
.. 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: POSIX & Windows
|
|
|
|
.. versionchanged:: 3.3.4
|
|
Windows support added
|
|
|
|
|
|
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.
|