736 lines
26 KiB
ReStructuredText
736 lines
26 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 other, older modules and functions, such as::
|
|
|
|
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 subprocess Module
|
|
---------------------------
|
|
|
|
This module defines one class called :class:`Popen`:
|
|
|
|
|
|
.. class:: Popen(args, bufsize=0, 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=())
|
|
|
|
Arguments are:
|
|
|
|
*args* should be a string, or a sequence of program arguments. The program
|
|
to execute is normally the first item in the args sequence or the string if
|
|
a string is given, but can be explicitly set by using the *executable*
|
|
argument. When *executable* is given, the first item in the args sequence
|
|
is still treated by most programs as the command name, which can then be
|
|
different from the actual executable name. On Unix, it becomes the display
|
|
name for the executing program in utilities such as :program:`ps`.
|
|
|
|
On Unix, with *shell=False* (default): In this case, the Popen class uses
|
|
:meth:`os.execvp` like behavior to execute the child program.
|
|
*args* should normally be a
|
|
sequence. If a string is specified for *args*, it will be used as the name
|
|
or path of the program to execute; this will only work if the program is
|
|
being given no arguments.
|
|
|
|
.. 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 Unix, with *shell=True*: If args is a string, it specifies the command
|
|
string 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, *Popen* does the equivalent of::
|
|
|
|
Popen(['/bin/sh', '-c', args[0], args[1], ...])
|
|
|
|
.. warning::
|
|
|
|
Executing shell commands that incorporate unsanitized input from an
|
|
untrusted source makes a program vulnerable to `shell injection
|
|
<http://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_,
|
|
a serious security flaw which can result in arbitrary command execution.
|
|
For this reason, the use of *shell=True* is **strongly discouraged** in cases
|
|
where the command string is constructed from external input::
|
|
|
|
>>> from subprocess import call
|
|
>>> filename = input("What file would you like to display?\n")
|
|
What file would you like to display?
|
|
non_existent; rm -rf / #
|
|
>>> call("cat " + filename, shell=True) # Uh-oh. This will end badly...
|
|
|
|
*shell=False* does not suffer from this vulnerability; the above Note may be
|
|
helpful in getting code using *shell=False* to work.
|
|
|
|
On Windows: the :class:`Popen` class uses CreateProcess() to execute the child
|
|
program, which operates on strings. If *args* is a sequence, it will be
|
|
converted to a string using the :meth:`list2cmdline` method. Please note that
|
|
not all MS Windows applications interpret the command line the same way:
|
|
:meth:`list2cmdline` is designed for applications using the same rules as the MS
|
|
C runtime.
|
|
|
|
*bufsize*, if given, has the same meaning as the corresponding argument to the
|
|
built-in open() function: :const:`0` means unbuffered, :const:`1` means line
|
|
buffered, any other positive value means use a buffer of (approximately) that
|
|
size. A negative *bufsize* means to use the system default, which usually means
|
|
fully buffered. The default value for *bufsize* is :const:`0` (unbuffered).
|
|
|
|
.. note::
|
|
|
|
If you experience performance issues, it is recommended that you try to
|
|
enable buffering by setting *bufsize* to either -1 or a large enough
|
|
positive value (such as 4096).
|
|
|
|
The *executable* argument specifies the program to execute. It is very seldom
|
|
needed: Usually, the program to execute is defined by the *args* argument. If
|
|
``shell=True``, the *executable* argument specifies which shell to use. On Unix,
|
|
the default shell is :file:`/bin/sh`. On Windows, the default shell is
|
|
specified by the :envvar:`COMSPEC` environment variable. The only reason you
|
|
would need to specify ``shell=True`` on Windows is where the command you
|
|
wish to execute is actually built in to the shell, eg ``dir``, ``copy``.
|
|
You don't need ``shell=True`` to run a batch file, nor to run a console-based
|
|
executable.
|
|
|
|
*stdin*, *stdout* and *stderr* specify the executed programs' 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 ``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.
|
|
(Unix 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. (Unix only).
|
|
The default varies by platform: Always true on Unix. On Windows it is
|
|
true when *stdin*/*stdout*/*stderr* are :const:`None`, false otherwise.
|
|
On Windows, if *close_fds* is true then no handles will be inherited by the
|
|
child process. Note that on Windows, you cannot set *close_fds* to true and
|
|
also redirect the standard handles by setting *stdin*, *stdout* or *stderr*.
|
|
|
|
.. versionchanged:: 3.2
|
|
The default for *close_fds* was changed from :const:`False` to
|
|
what is described above.
|
|
|
|
*pass_fds* is an optional sequence of file descriptors to keep open
|
|
between the parent and child. Providing any *pass_fds* forces
|
|
*close_fds* to be :const:`True`. (Unix only)
|
|
|
|
.. versionadded:: 3.2
|
|
The *pass_fds* parameter was added.
|
|
|
|
If *cwd* is not ``None``, the child's current directory will be changed to *cwd*
|
|
before it is executed. Note that this directory is not considered when
|
|
searching the executable, so you can't specify the program's path relative to
|
|
*cwd*.
|
|
|
|
If *restore_signals* is True (the default) all signals that Python has set to
|
|
SIG_IGN are restored to SIG_DFL in the child process before the exec.
|
|
Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals.
|
|
(Unix only)
|
|
|
|
.. versionchanged:: 3.2
|
|
*restore_signals* was added.
|
|
|
|
If *start_new_session* is True the setsid() system call will be made in the
|
|
child process prior to the execution of the subprocess. (Unix only)
|
|
|
|
.. versionchanged:: 3.2
|
|
*start_new_session* was added.
|
|
|
|
If *env* is not ``None``, it must be a mapping that defines the environment
|
|
variables for the new process; these are used instead of the default
|
|
behavior of inheriting the current process' environment.
|
|
|
|
.. note::
|
|
|
|
If specified, *env* must provide any variables required for the program to
|
|
execute. On Windows, in order to run a `side-by-side assembly`_ the
|
|
specified *env* **must** include a valid :envvar:`SystemRoot`.
|
|
|
|
.. _side-by-side assembly: http://en.wikipedia.org/wiki/Side-by-Side_Assembly
|
|
|
|
If *universal_newlines* is :const:`True`, the file objects stdout and stderr are
|
|
opened as text files, but lines may be terminated by any of ``'\n'``, the Unix
|
|
end-of-line convention, ``'\r'``, the old Macintosh convention or ``'\r\n'``, the
|
|
Windows convention. All of these external representations are seen as ``'\n'``
|
|
by the Python program.
|
|
|
|
.. note::
|
|
|
|
This feature is only available if Python is built with universal newline
|
|
support (the default). Also, the newlines attribute of the file objects
|
|
:attr:`stdout`, :attr:`stdin` and :attr:`stderr` are not updated by the
|
|
:meth:`communicate` method.
|
|
|
|
The *startupinfo* and *creationflags*, if given, will be passed to the
|
|
underlying CreateProcess() function. They can specify things such as appearance
|
|
of the main window and priority for the new process. (Windows only)
|
|
|
|
Popen objects are supported as context managers via the :keyword:`with` statement,
|
|
closing any open file descriptors on exit.
|
|
::
|
|
|
|
with Popen(["ifconfig"], stdout=PIPE) as proc:
|
|
log.write(proc.stdout.read())
|
|
|
|
.. versionchanged:: 3.2
|
|
Added context manager support.
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
Convenience Functions
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
This module also defines four shortcut functions:
|
|
|
|
|
|
.. function:: call(*popenargs, timeout=None, **kwargs)
|
|
|
|
Run command with arguments. Wait for command to complete, then return the
|
|
:attr:`returncode` attribute.
|
|
|
|
The arguments are the same as for the :class:`Popen` constructor, with the
|
|
exception of the *timeout* argument, which is given to :meth:`Popen.wait`.
|
|
Example::
|
|
|
|
>>> retcode = subprocess.call(["ls", "-l"])
|
|
|
|
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.
|
|
|
|
.. warning::
|
|
|
|
Like :meth:`Popen.wait`, this will deadlock when using
|
|
``stdout=PIPE`` and/or ``stderr=PIPE`` and the child process
|
|
generates enough output to a pipe such that it blocks waiting
|
|
for the OS pipe buffer to accept more data.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. function:: check_call(*popenargs, timeout=None, **kwargs)
|
|
|
|
Run command with arguments. Wait for command to complete. If the exit code was
|
|
zero then return, otherwise raise :exc:`CalledProcessError`. The
|
|
:exc:`CalledProcessError` object will have the return code in the
|
|
:attr:`returncode` attribute.
|
|
|
|
The arguments are the same as for the :func:`call` function. Example::
|
|
|
|
>>> subprocess.check_call(["ls", "-l"])
|
|
0
|
|
|
|
As in the :func:`call` function, if the timeout expires, the child process
|
|
will be killed and the wait retried. The :exc:`TimeoutExpired` exception
|
|
will be re-raised after the child process has terminated.
|
|
|
|
.. warning::
|
|
|
|
See the warning for :func:`call`.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. function:: check_output(*popenargs, timeout=None, **kwargs)
|
|
|
|
Run command with arguments and return its output as a byte string.
|
|
|
|
If the exit code was non-zero it raises a :exc:`CalledProcessError`. The
|
|
:exc:`CalledProcessError` object will have the return code in the
|
|
:attr:`returncode` attribute and output in the :attr:`output` attribute.
|
|
|
|
The arguments are the same as for the :func:`call` function. Example::
|
|
|
|
>>> subprocess.check_output(["ls", "-l", "/dev/null"])
|
|
b'crw-rw-rw- 1 root root 1, 3 Oct 18 2007 /dev/null\n'
|
|
|
|
The stdout argument is not allowed as it is used internally.
|
|
To capture standard error in the result, use ``stderr=subprocess.STDOUT``::
|
|
|
|
>>> subprocess.check_output(
|
|
... ["/bin/sh", "-c", "ls non_existent_file; exit 0"],
|
|
... stderr=subprocess.STDOUT)
|
|
b'ls: non_existent_file: No such file or directory\n'
|
|
|
|
As in the :func:`call` function, if the timeout expires, the child process
|
|
will be killed and the wait retried. The :exc:`TimeoutExpired` exception
|
|
will be re-raised after the child process has terminated. The output from
|
|
the child process so far will be in the :attr:`output` attribute of the
|
|
exception.
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. function:: getstatusoutput(cmd)
|
|
|
|
Return ``(status, output)`` of executing *cmd* in a shell.
|
|
|
|
Execute the string *cmd* in a shell with :func:`os.popen` and return a 2-tuple
|
|
``(status, output)``. *cmd* is actually run as ``{ cmd ; } 2>&1``, so that the
|
|
returned output will contain output or error messages. A trailing newline is
|
|
stripped from the output. The exit status for the command can be interpreted
|
|
according to the rules for the C function :c:func:`wait`. Example::
|
|
|
|
>>> subprocess.getstatusoutput('ls /bin/ls')
|
|
(0, '/bin/ls')
|
|
>>> subprocess.getstatusoutput('cat /bin/junk')
|
|
(256, 'cat: /bin/junk: No such file or directory')
|
|
>>> subprocess.getstatusoutput('/bin/junk')
|
|
(256, 'sh: /bin/junk: not found')
|
|
|
|
Availability: UNIX.
|
|
|
|
|
|
.. function:: getoutput(cmd)
|
|
|
|
Return output (stdout and stderr) of executing *cmd* in a shell.
|
|
|
|
Like :func:`getstatusoutput`, except the exit status is ignored and the return
|
|
value is a string containing the command's output. Example::
|
|
|
|
>>> subprocess.getoutput('ls /bin/ls')
|
|
'/bin/ls'
|
|
|
|
Availability: UNIX.
|
|
|
|
|
|
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.
|
|
|
|
check_call() will raise :exc:`CalledProcessError`, if the called process returns
|
|
a non-zero return code.
|
|
|
|
All of the functions and methods that accept a *timeout* parameter, such as
|
|
:func:`call` and :meth:`Popen.communicate` will raise :exc:`TimeoutExpired` if
|
|
the timeout expires before the process exits.
|
|
|
|
Exceptions defined in this module all inherit from :exc:`SubprocessError`.
|
|
|
|
.. versionadded:: 3.3
|
|
The :exc:`SubprocessError` base class was added.
|
|
|
|
|
|
Security
|
|
^^^^^^^^
|
|
|
|
Unlike some other popen functions, this implementation will never call /bin/sh
|
|
implicitly. This means that all characters, including shell metacharacters, can
|
|
safely be passed to child processes.
|
|
|
|
|
|
Popen Objects
|
|
-------------
|
|
|
|
Instances of the :class:`Popen` class have the following methods:
|
|
|
|
|
|
.. method:: Popen.poll()
|
|
|
|
Check if child process has terminated. Set and return :attr:`returncode`
|
|
attribute.
|
|
|
|
|
|
.. method:: Popen.wait(timeout=None)
|
|
|
|
Wait for child process to terminate. Set and return :attr:`returncode`
|
|
attribute.
|
|
|
|
If the process does not terminate after *timeout* seconds, raise a
|
|
:exc:`TimeoutExpired` exception. It is safe to catch this exception and
|
|
retry the wait.
|
|
|
|
.. warning::
|
|
|
|
This will deadlock when using ``stdout=PIPE`` and/or
|
|
``stderr=PIPE`` and the child process generates enough output to
|
|
a pipe such that it blocks waiting for the OS pipe buffer to
|
|
accept more data. Use :meth:`communicate` to avoid that.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. method:: Popen.communicate(input=None, timeout=None)
|
|
|
|
Interact with process: Send data to stdin. Read data from stdout and stderr,
|
|
until end-of-file is reached. Wait for process to terminate. The optional
|
|
*input* argument should be a byte string to be sent to the child process, or
|
|
``None``, if no data should be sent to the child.
|
|
|
|
:meth:`communicate` returns a tuple ``(stdoutdata, stderrdata)``.
|
|
|
|
Note that if you want to send data to the process's stdin, you need to create
|
|
the Popen object with ``stdin=PIPE``. Similarly, to get anything other than
|
|
``None`` in the result tuple, you need to give ``stdout=PIPE`` and/or
|
|
``stderr=PIPE`` too.
|
|
|
|
If the process does not terminate after *timeout* seconds, a
|
|
:exc:`TimeoutExpired` exception will be raised. Catching this exception and
|
|
retrying communication will not lose any output.
|
|
|
|
The child process is not killed if the timeout expires, so in order to
|
|
cleanup properly a well-behaved application should kill the child process and
|
|
finish communication::
|
|
|
|
proc = subprocess.Popen(...)
|
|
try:
|
|
outs, errs = proc.communicate(timeout=15)
|
|
except TimeoutExpired:
|
|
proc.kill()
|
|
outs, errs = proc.communicate()
|
|
|
|
.. note::
|
|
|
|
The data read is buffered in memory, so do not use this method if the data
|
|
size is large or unlimited.
|
|
|
|
.. versionchanged:: 3.3
|
|
*timeout* was added.
|
|
|
|
|
|
.. method:: Popen.send_signal(signal)
|
|
|
|
Sends the signal *signal* to the child.
|
|
|
|
.. note::
|
|
|
|
On Windows, SIGTERM is an alias for :meth:`terminate`. CTRL_C_EVENT and
|
|
CTRL_BREAK_EVENT can be sent to processes started with a *creationflags*
|
|
parameter which includes `CREATE_NEW_PROCESS_GROUP`.
|
|
|
|
|
|
.. method:: Popen.terminate()
|
|
|
|
Stop the child. On Posix OSs the method sends SIGTERM to the
|
|
child. On Windows the Win32 API function :c:func:`TerminateProcess` is called
|
|
to stop the child.
|
|
|
|
|
|
.. method:: Popen.kill()
|
|
|
|
Kills the child. On Posix OSs the function sends SIGKILL to the child.
|
|
On Windows :meth:`kill` is an alias for :meth:`terminate`.
|
|
|
|
|
|
The following attributes are also available:
|
|
|
|
.. warning::
|
|
|
|
Use :meth:`communicate` rather than :attr:`.stdin.write <stdin>`,
|
|
:attr:`.stdout.read <stdout>` or :attr:`.stderr.read <stderr>` to avoid
|
|
deadlocks due to any of the other OS pipe buffers filling up and blocking the
|
|
child process.
|
|
|
|
|
|
.. attribute:: Popen.stdin
|
|
|
|
If the *stdin* argument was :data:`PIPE`, this attribute is a :term:`file
|
|
object` that provides input to the child process. Otherwise, it is ``None``.
|
|
|
|
|
|
.. attribute:: Popen.stdout
|
|
|
|
If the *stdout* argument was :data:`PIPE`, this attribute is a :term:`file
|
|
object` that provides output from the child process. Otherwise, it is ``None``.
|
|
|
|
|
|
.. attribute:: Popen.stderr
|
|
|
|
If the *stderr* argument was :data:`PIPE`, this attribute is a :term:`file
|
|
object` that provides error output from the child process. Otherwise, it is
|
|
``None``.
|
|
|
|
|
|
.. attribute:: Popen.pid
|
|
|
|
The process ID of the child process.
|
|
|
|
Note that if you set the *shell* argument to ``True``, this is the process ID
|
|
of the spawned shell.
|
|
|
|
|
|
.. attribute:: Popen.returncode
|
|
|
|
The child return code, set by :meth:`poll` and :meth:`wait` (and indirectly
|
|
by :meth:`communicate`). A ``None`` value indicates that the process
|
|
hasn't terminated yet.
|
|
|
|
A negative value ``-N`` indicates that the child was terminated by signal
|
|
``N`` (Unix only).
|
|
|
|
|
|
.. _subprocess-replacements:
|
|
|
|
Replacing Older Functions with the subprocess Module
|
|
----------------------------------------------------
|
|
|
|
In this section, "a ==> b" means that b can be used as a replacement for a.
|
|
|
|
.. note::
|
|
|
|
All functions in this section fail (more or less) silently if the executed
|
|
program cannot be found; this module raises an :exc:`OSError` exception.
|
|
|
|
In the following examples, we assume that the subprocess module is imported with
|
|
"from subprocess import \*".
|
|
|
|
|
|
Replacing /bin/sh shell backquote
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
output=`mycmd myarg`
|
|
==>
|
|
output = Popen(["mycmd", "myarg"], stdout=PIPE).communicate()[0]
|
|
|
|
|
|
Replacing shell pipeline
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
output=`dmesg | grep hda`
|
|
==>
|
|
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.
|
|
|
|
Replacing :func:`os.system`
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
::
|
|
|
|
sts = os.system("mycmd" + " myarg")
|
|
==>
|
|
p = Popen("mycmd" + " myarg", shell=True)
|
|
sts = os.waitpid(p.pid, 0)[1]
|
|
|
|
Notes:
|
|
|
|
* Calling the program through the shell is usually not required.
|
|
|
|
* It's easier to look at the :attr:`returncode` attribute than the exit status.
|
|
|
|
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.
|