Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | :mod:`subprocess` --- Subprocess management |
| 2 | =========================================== |
| 3 | |
| 4 | .. module:: subprocess |
| 5 | :synopsis: Subprocess management. |
| 6 | .. moduleauthor:: Peter Åstrand <astrand@lysator.liu.se> |
| 7 | .. sectionauthor:: Peter Åstrand <astrand@lysator.liu.se> |
| 8 | |
| 9 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 10 | The :mod:`subprocess` module allows you to spawn new processes, connect to their |
| 11 | input/output/error pipes, and obtain their return codes. This module intends to |
| 12 | replace several other, older modules and functions, such as:: |
| 13 | |
| 14 | os.system |
| 15 | os.spawn* |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 16 | |
| 17 | Information about how the :mod:`subprocess` module can be used to replace these |
| 18 | modules and functions can be found in the following sections. |
| 19 | |
Benjamin Peterson | 4118174 | 2008-07-02 20:22:54 +0000 | [diff] [blame] | 20 | .. seealso:: |
| 21 | |
| 22 | :pep:`324` -- PEP proposing the subprocess module |
| 23 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 24 | |
| 25 | Using the subprocess Module |
| 26 | --------------------------- |
| 27 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 28 | The recommended approach to invoking subprocesses is to use the following |
| 29 | convenience functions for all use cases they can handle. For more advanced |
| 30 | use cases, the underlying :class:`Popen` interface can be used directly. |
| 31 | |
| 32 | |
| 33 | .. function:: call(args, *, stdin=None, stdout=None, stderr=None, shell=False) |
| 34 | |
| 35 | Run the command described by *args*. Wait for command to complete, then |
| 36 | return the :attr:`returncode` attribute. |
| 37 | |
| 38 | The arguments shown above are merely the most common ones, described below |
| 39 | in :ref:`frequently-used-arguments` (hence the slightly odd notation in |
| 40 | the abbreviated signature). The full function signature is the same as |
| 41 | that of the :class:`Popen` constructor - this functions passes all |
| 42 | supplied arguments directly through to that interface. |
| 43 | |
| 44 | Examples:: |
| 45 | |
| 46 | >>> subprocess.call(["ls", "-l"]) |
| 47 | 0 |
| 48 | |
| 49 | >>> subprocess.call("exit 1", shell=True) |
| 50 | 1 |
| 51 | |
| 52 | .. warning:: |
| 53 | |
| 54 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 55 | if combined with untrusted input. See the warning under |
| 56 | :ref:`frequently-used-arguments` for details. |
| 57 | |
| 58 | .. note:: |
| 59 | |
| 60 | Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As |
| 61 | the pipes are not being read in the current process, the child |
| 62 | process may block if it generates enough output to a pipe to fill up |
| 63 | the OS pipe buffer. |
| 64 | |
| 65 | |
| 66 | .. function:: check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False) |
| 67 | |
| 68 | Run command with arguments. Wait for command to complete. If the return |
| 69 | code was zero then return, otherwise raise :exc:`CalledProcessError`. The |
| 70 | :exc:`CalledProcessError` object will have the return code in the |
| 71 | :attr:`returncode` attribute. |
| 72 | |
| 73 | The arguments shown above are merely the most common ones, described below |
| 74 | in :ref:`frequently-used-arguments` (hence the slightly odd notation in |
| 75 | the abbreviated signature). The full function signature is the same as |
| 76 | that of the :class:`Popen` constructor - this functions passes all |
| 77 | supplied arguments directly through to that interface. |
| 78 | |
| 79 | Examples:: |
| 80 | |
| 81 | >>> subprocess.check_call(["ls", "-l"]) |
| 82 | 0 |
| 83 | |
| 84 | >>> subprocess.check_call("exit 1", shell=True) |
| 85 | Traceback (most recent call last): |
| 86 | ... |
| 87 | subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 |
| 88 | |
| 89 | .. versionadded:: 2.5 |
| 90 | |
| 91 | .. warning:: |
| 92 | |
| 93 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 94 | if combined with untrusted input. See the warning under |
| 95 | :ref:`frequently-used-arguments` for details. |
| 96 | |
| 97 | .. note:: |
| 98 | |
| 99 | Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As |
| 100 | the pipes are not being read in the current process, the child |
| 101 | process may block if it generates enough output to a pipe to fill up |
| 102 | the OS pipe buffer. |
| 103 | |
| 104 | |
| 105 | .. function:: check_output(args, *, stdin=None, stderr=None, shell=False, universal_newlines=False) |
| 106 | |
| 107 | Run command with arguments and return its output as a byte string. |
| 108 | |
| 109 | If the return code was non-zero it raises a :exc:`CalledProcessError`. The |
| 110 | :exc:`CalledProcessError` object will have the return code in the |
| 111 | :attr:`returncode` attribute and any output in the :attr:`output` |
| 112 | attribute. |
| 113 | |
| 114 | The arguments shown above are merely the most common ones, described below |
| 115 | in :ref:`frequently-used-arguments` (hence the slightly odd notation in |
| 116 | the abbreviated signature). The full function signature is largely the |
| 117 | same as that of the :class:`Popen` constructor, except that *stdout* is |
| 118 | not permitted as it is used internally. All other supplied arguments are |
| 119 | passed directly through to the :class:`Popen` constructor. |
| 120 | |
| 121 | Examples:: |
| 122 | |
| 123 | >>> subprocess.check_output(["echo", "Hello World!"]) |
| 124 | b'Hello World!\n' |
| 125 | |
| 126 | >>> subprocess.check_output(["echo", "Hello World!"], universal_newlines=True) |
| 127 | 'Hello World!\n' |
| 128 | |
| 129 | >>> subprocess.check_output("exit 1", shell=True) |
| 130 | Traceback (most recent call last): |
| 131 | ... |
| 132 | subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 |
| 133 | |
| 134 | By default, this function will return the data as encoded bytes. The actual |
| 135 | encoding of the output data may depend on the command being invoked, so the |
| 136 | decoding to text will often need to be handled at the application level. |
| 137 | |
| 138 | This behaviour may be overridden by setting *universal_newlines* to |
Andrew Svetlov | 50be452 | 2012-08-13 22:09:04 +0300 | [diff] [blame^] | 139 | ``True`` as described below in :ref:`frequently-used-arguments`. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 140 | |
| 141 | To also capture standard error in the result, use |
| 142 | ``stderr=subprocess.STDOUT``:: |
| 143 | |
| 144 | >>> subprocess.check_output( |
| 145 | ... "ls non_existent_file; exit 0", |
| 146 | ... stderr=subprocess.STDOUT, |
| 147 | ... shell=True) |
| 148 | 'ls: non_existent_file: No such file or directory\n' |
| 149 | |
| 150 | .. versionadded:: 2.7 |
| 151 | |
| 152 | .. warning:: |
| 153 | |
| 154 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 155 | if combined with untrusted input. See the warning under |
| 156 | :ref:`frequently-used-arguments` for details. |
| 157 | |
| 158 | .. note:: |
| 159 | |
| 160 | Do not use ``stderr=PIPE`` with this function. As the pipe is not being |
| 161 | read in the current process, the child process may block if it |
| 162 | generates enough output to the pipe to fill up the OS pipe buffer. |
| 163 | |
| 164 | |
| 165 | .. data:: PIPE |
| 166 | |
| 167 | Special value that can be used as the *stdin*, *stdout* or *stderr* argument |
| 168 | to :class:`Popen` and indicates that a pipe to the standard stream should be |
| 169 | opened. |
| 170 | |
| 171 | |
| 172 | .. data:: STDOUT |
| 173 | |
| 174 | Special value that can be used as the *stderr* argument to :class:`Popen` and |
| 175 | indicates that standard error should go into the same handle as standard |
| 176 | output. |
| 177 | |
| 178 | |
Andrew Svetlov | eec6420 | 2012-08-09 15:20:45 +0300 | [diff] [blame] | 179 | .. exception:: CalledProcessError |
| 180 | |
| 181 | Exception raised when a process run by :func:`check_call` or |
| 182 | :func:`check_output` returns a non-zero exit status. |
| 183 | |
| 184 | .. attribute:: returncode |
| 185 | |
| 186 | Exit status of the child process. |
| 187 | |
| 188 | .. attribute:: cmd |
| 189 | |
| 190 | Command that was used to spawn the child process. |
| 191 | |
| 192 | .. attribute:: output |
| 193 | |
| 194 | Output of the child process if this exception is raised by |
| 195 | :func:`check_output`. Otherwise, ``None``. |
| 196 | |
| 197 | |
| 198 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 199 | .. _frequently-used-arguments: |
| 200 | |
| 201 | Frequently Used Arguments |
| 202 | ^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 203 | |
| 204 | To support a wide variety of use cases, the :class:`Popen` constructor (and |
| 205 | the convenience functions) accept a large number of optional arguments. For |
| 206 | most typical use cases, many of these arguments can be safely left at their |
| 207 | default values. The arguments that are most commonly needed are: |
| 208 | |
| 209 | *args* is required for all calls and should be a string, or a sequence of |
| 210 | program arguments. Providing a sequence of arguments is generally |
| 211 | preferred, as it allows the module to take care of any required escaping |
| 212 | and quoting of arguments (e.g. to permit spaces in file names). If passing |
| 213 | a single string, either *shell* must be :const:`True` (see below) or else |
| 214 | the string must simply name the program to be executed without specifying |
| 215 | any arguments. |
| 216 | |
| 217 | *stdin*, *stdout* and *stderr* specify the executed program's standard input, |
| 218 | standard output and standard error file handles, respectively. Valid values |
| 219 | are :data:`PIPE`, an existing file descriptor (a positive integer), an |
| 220 | existing file object, and ``None``. :data:`PIPE` indicates that a new pipe |
| 221 | to the child should be created. With the default settings of ``None``, no |
| 222 | redirection will occur; the child's file handles will be inherited from the |
| 223 | parent. Additionally, *stderr* can be :data:`STDOUT`, which indicates that |
| 224 | the stderr data from the child process should be captured into the same file |
| 225 | handle as for stdout. |
| 226 | |
Andrew Svetlov | 50be452 | 2012-08-13 22:09:04 +0300 | [diff] [blame^] | 227 | If *universal_newlines* is ``True``, the file objects *stdin*, *stdout* |
| 228 | and *stderr* will be opened as text streams with universal newlines support, |
| 229 | using the encoding returned by :func:`locale.getpreferredencoding`. |
| 230 | For *stdin*, line ending characters ``'\n'`` in the input will be converted |
| 231 | to the default line separator :data:`os.linesep`. For *stdout* and |
| 232 | *stderr*, all line endings in the output will be converted to ``'\n'``. |
| 233 | For more information see the documentation of the :class:`io.TextIOWrapper` |
| 234 | class when the *newline* argument to its constructor is ``None``. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 235 | |
Andrew Svetlov | 50be452 | 2012-08-13 22:09:04 +0300 | [diff] [blame^] | 236 | .. note:: |
| 237 | |
| 238 | The *universal_newlines* feature is supported only if Python is built |
| 239 | with universal newline support (the default). Also, the newlines |
| 240 | attribute of the file objects :attr:`Popen.stdin`, :attr:`Popen.stdout` |
| 241 | and :attr:`Popen.stderr` are not updated by the |
| 242 | :meth:`Popen.communicate` method. |
| 243 | |
| 244 | If *shell* is ``True``, the specified command will be executed through |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 245 | the shell. This can be useful if you are using Python primarily for the |
| 246 | enhanced control flow it offers over most system shells and still want |
| 247 | access to other shell features such as filename wildcards, shell pipes and |
| 248 | environment variable expansion. |
| 249 | |
| 250 | .. warning:: |
| 251 | |
| 252 | Executing shell commands that incorporate unsanitized input from an |
| 253 | untrusted source makes a program vulnerable to `shell injection |
| 254 | <http://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_, |
| 255 | a serious security flaw which can result in arbitrary command execution. |
| 256 | For this reason, the use of *shell=True* is **strongly discouraged** in cases |
| 257 | where the command string is constructed from external input:: |
| 258 | |
| 259 | >>> from subprocess import call |
| 260 | >>> filename = input("What file would you like to display?\n") |
| 261 | What file would you like to display? |
| 262 | non_existent; rm -rf / # |
| 263 | >>> call("cat " + filename, shell=True) # Uh-oh. This will end badly... |
| 264 | |
| 265 | ``shell=False`` disables all shell based features, but does not suffer |
| 266 | from this vulnerability; see the Note in the :class:`Popen` constructor |
| 267 | documentation for helpful hints in getting ``shell=False`` to work. |
| 268 | |
| 269 | These options, along with all of the other options, are described in more |
| 270 | detail in the :class:`Popen` constructor documentation. |
| 271 | |
| 272 | |
Sandro Tosi | 1526ad1 | 2011-12-25 11:27:37 +0100 | [diff] [blame] | 273 | Popen Constructor |
Sandro Tosi | 3e6c814 | 2011-12-25 17:14:11 +0100 | [diff] [blame] | 274 | ^^^^^^^^^^^^^^^^^ |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 275 | |
| 276 | The underlying process creation and management in this module is handled by |
| 277 | the :class:`Popen` class. It offers a lot of flexibility so that developers |
| 278 | are able to handle the less common cases not covered by the convenience |
| 279 | functions. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 280 | |
| 281 | |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 282 | .. 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=()) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 283 | |
| 284 | Arguments are: |
| 285 | |
Benjamin Peterson | d18de0e | 2008-07-31 20:21:46 +0000 | [diff] [blame] | 286 | *args* should be a string, or a sequence of program arguments. The program |
Benjamin Peterson | fa0d703 | 2009-06-01 22:42:33 +0000 | [diff] [blame] | 287 | to execute is normally the first item in the args sequence or the string if |
| 288 | a string is given, but can be explicitly set by using the *executable* |
| 289 | argument. When *executable* is given, the first item in the args sequence |
| 290 | is still treated by most programs as the command name, which can then be |
| 291 | different from the actual executable name. On Unix, it becomes the display |
| 292 | name for the executing program in utilities such as :program:`ps`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 293 | |
| 294 | On Unix, with *shell=False* (default): In this case, the Popen class uses |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 295 | :meth:`os.execvp` like behavior to execute the child program. |
| 296 | *args* should normally be a |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 297 | sequence. If a string is specified for *args*, it will be used as the name |
| 298 | or path of the program to execute; this will only work if the program is |
| 299 | being given no arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 300 | |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 301 | .. note:: |
| 302 | |
| 303 | :meth:`shlex.split` can be useful when determining the correct |
| 304 | tokenization for *args*, especially in complex cases:: |
| 305 | |
| 306 | >>> import shlex, subprocess |
R. David Murray | 73bc75b | 2010-02-05 16:25:12 +0000 | [diff] [blame] | 307 | >>> command_line = input() |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 308 | /bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'" |
| 309 | >>> args = shlex.split(command_line) |
| 310 | >>> print(args) |
| 311 | ['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"] |
| 312 | >>> p = subprocess.Popen(args) # Success! |
| 313 | |
| 314 | Note in particular that options (such as *-input*) and arguments (such |
| 315 | as *eggs.txt*) that are separated by whitespace in the shell go in separate |
| 316 | list elements, while arguments that need quoting or backslash escaping when |
| 317 | used in the shell (such as filenames containing spaces or the *echo* command |
| 318 | shown above) are single list elements. |
| 319 | |
| 320 | On Unix, with *shell=True*: If args is a string, it specifies the command |
| 321 | string to execute through the shell. This means that the string must be |
| 322 | formatted exactly as it would be when typed at the shell prompt. This |
| 323 | includes, for example, quoting or backslash escaping filenames with spaces in |
| 324 | them. If *args* is a sequence, the first item specifies the command string, and |
| 325 | any additional items will be treated as additional arguments to the shell |
| 326 | itself. That is to say, *Popen* does the equivalent of:: |
| 327 | |
| 328 | Popen(['/bin/sh', '-c', args[0], args[1], ...]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 329 | |
R. David Murray | c7399d0 | 2010-11-12 00:35:31 +0000 | [diff] [blame] | 330 | .. warning:: |
| 331 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 332 | Enabling this option can be a security hazard if combined with untrusted |
| 333 | input. See the warning under :ref:`frequently-used-arguments` |
| 334 | for details. |
R. David Murray | c7399d0 | 2010-11-12 00:35:31 +0000 | [diff] [blame] | 335 | |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 336 | On Windows: the :class:`Popen` class uses CreateProcess() to execute the |
| 337 | child program, which operates on strings. If *args* is a sequence, it will |
| 338 | be converted to a string in a manner described in |
| 339 | :ref:`converting-argument-sequence`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 340 | |
| 341 | *bufsize*, if given, has the same meaning as the corresponding argument to the |
| 342 | built-in open() function: :const:`0` means unbuffered, :const:`1` means line |
| 343 | buffered, any other positive value means use a buffer of (approximately) that |
| 344 | size. A negative *bufsize* means to use the system default, which usually means |
| 345 | fully buffered. The default value for *bufsize* is :const:`0` (unbuffered). |
| 346 | |
Antoine Pitrou | 4b87620 | 2010-06-02 17:10:49 +0000 | [diff] [blame] | 347 | .. note:: |
| 348 | |
| 349 | If you experience performance issues, it is recommended that you try to |
| 350 | enable buffering by setting *bufsize* to either -1 or a large enough |
| 351 | positive value (such as 4096). |
| 352 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 353 | The *executable* argument specifies the program to execute. It is very seldom |
| 354 | needed: Usually, the program to execute is defined by the *args* argument. If |
| 355 | ``shell=True``, the *executable* argument specifies which shell to use. On Unix, |
| 356 | the default shell is :file:`/bin/sh`. On Windows, the default shell is |
Alexandre Vassalotti | 260484d | 2009-07-17 11:43:26 +0000 | [diff] [blame] | 357 | specified by the :envvar:`COMSPEC` environment variable. The only reason you |
| 358 | would need to specify ``shell=True`` on Windows is where the command you |
| 359 | wish to execute is actually built in to the shell, eg ``dir``, ``copy``. |
| 360 | You don't need ``shell=True`` to run a batch file, nor to run a console-based |
| 361 | executable. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 362 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 363 | *stdin*, *stdout* and *stderr* specify the executed program's standard input, |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 364 | standard output and standard error file handles, respectively. Valid values |
| 365 | are :data:`PIPE`, an existing file descriptor (a positive integer), an |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 366 | existing :term:`file object`, and ``None``. :data:`PIPE` indicates that a |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 367 | new pipe to the child should be created. With the default settings of |
| 368 | ``None``, no redirection will occur; the child's file handles will be |
| 369 | inherited from the parent. Additionally, *stderr* can be :data:`STDOUT`, |
| 370 | which indicates that the stderr data from the applications should be |
| 371 | captured into the same file handle as for stdout. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 372 | |
| 373 | If *preexec_fn* is set to a callable object, this object will be called in the |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 374 | child process just before the child is executed. |
| 375 | (Unix only) |
| 376 | |
| 377 | .. warning:: |
| 378 | |
| 379 | The *preexec_fn* parameter is not safe to use in the presence of threads |
| 380 | in your application. The child process could deadlock before exec is |
| 381 | called. |
| 382 | If you must use it, keep it trivial! Minimize the number of libraries |
| 383 | you call into. |
| 384 | |
| 385 | .. note:: |
| 386 | |
| 387 | If you need to modify the environment for the child use the *env* |
| 388 | parameter rather than doing it in a *preexec_fn*. |
| 389 | The *start_new_session* parameter can take the place of a previously |
| 390 | common use of *preexec_fn* to call os.setsid() in the child. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 391 | |
| 392 | If *close_fds* is true, all file descriptors except :const:`0`, :const:`1` and |
| 393 | :const:`2` will be closed before the child process is executed. (Unix only). |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 394 | The default varies by platform: Always true on Unix. On Windows it is |
| 395 | true when *stdin*/*stdout*/*stderr* are :const:`None`, false otherwise. |
Gregory P. Smith | d23047b | 2010-12-04 09:10:44 +0000 | [diff] [blame] | 396 | On Windows, if *close_fds* is true then no handles will be inherited by the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 397 | child process. Note that on Windows, you cannot set *close_fds* to true and |
| 398 | also redirect the standard handles by setting *stdin*, *stdout* or *stderr*. |
| 399 | |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 400 | .. versionchanged:: 3.2 |
| 401 | The default for *close_fds* was changed from :const:`False` to |
| 402 | what is described above. |
| 403 | |
| 404 | *pass_fds* is an optional sequence of file descriptors to keep open |
| 405 | between the parent and child. Providing any *pass_fds* forces |
| 406 | *close_fds* to be :const:`True`. (Unix only) |
| 407 | |
| 408 | .. versionadded:: 3.2 |
| 409 | The *pass_fds* parameter was added. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 410 | |
| 411 | If *cwd* is not ``None``, the child's current directory will be changed to *cwd* |
| 412 | before it is executed. Note that this directory is not considered when |
| 413 | searching the executable, so you can't specify the program's path relative to |
| 414 | *cwd*. |
| 415 | |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 416 | If *restore_signals* is True (the default) all signals that Python has set to |
| 417 | SIG_IGN are restored to SIG_DFL in the child process before the exec. |
| 418 | Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. |
| 419 | (Unix only) |
| 420 | |
| 421 | .. versionchanged:: 3.2 |
| 422 | *restore_signals* was added. |
| 423 | |
| 424 | If *start_new_session* is True the setsid() system call will be made in the |
| 425 | child process prior to the execution of the subprocess. (Unix only) |
| 426 | |
| 427 | .. versionchanged:: 3.2 |
| 428 | *start_new_session* was added. |
| 429 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 430 | If *env* is not ``None``, it must be a mapping that defines the environment |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 431 | variables for the new process; these are used instead of the default |
| 432 | behavior of inheriting the current process' environment. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 433 | |
R. David Murray | 1055e89 | 2009-04-16 18:15:32 +0000 | [diff] [blame] | 434 | .. note:: |
R. David Murray | f4ac149 | 2009-04-15 22:35:15 +0000 | [diff] [blame] | 435 | |
Georg Brandl | 2708f3a | 2009-12-20 14:38:23 +0000 | [diff] [blame] | 436 | If specified, *env* must provide any variables required for the program to |
| 437 | execute. On Windows, in order to run a `side-by-side assembly`_ the |
| 438 | specified *env* **must** include a valid :envvar:`SystemRoot`. |
R. David Murray | f4ac149 | 2009-04-15 22:35:15 +0000 | [diff] [blame] | 439 | |
R. David Murray | 1055e89 | 2009-04-16 18:15:32 +0000 | [diff] [blame] | 440 | .. _side-by-side assembly: http://en.wikipedia.org/wiki/Side-by-Side_Assembly |
| 441 | |
Andrew Svetlov | 50be452 | 2012-08-13 22:09:04 +0300 | [diff] [blame^] | 442 | If *universal_newlines* is ``True``, the file objects *stdin*, *stdout* |
| 443 | and *stderr* are opened as text files with universal newlines support, as |
| 444 | described above in :ref:`frequently-used-arguments`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 445 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 446 | If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is |
| 447 | passed to the underlying ``CreateProcess`` function. |
Brian Curtin | 3040193 | 2011-04-29 22:20:57 -0500 | [diff] [blame] | 448 | *creationflags*, if given, can be :data:`CREATE_NEW_CONSOLE` or |
| 449 | :data:`CREATE_NEW_PROCESS_GROUP`. (Windows only) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 450 | |
Gregory P. Smith | c9557af | 2011-05-11 22:18:23 -0700 | [diff] [blame] | 451 | Popen objects are supported as context managers via the :keyword:`with` statement: |
| 452 | on exit, standard file descriptors are closed, and the process is waited for. |
Brian Curtin | 79cdb66 | 2010-12-03 02:46:02 +0000 | [diff] [blame] | 453 | :: |
| 454 | |
| 455 | with Popen(["ifconfig"], stdout=PIPE) as proc: |
| 456 | log.write(proc.stdout.read()) |
| 457 | |
| 458 | .. versionchanged:: 3.2 |
| 459 | Added context manager support. |
| 460 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 461 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 462 | Exceptions |
| 463 | ^^^^^^^^^^ |
| 464 | |
| 465 | Exceptions raised in the child process, before the new program has started to |
| 466 | execute, will be re-raised in the parent. Additionally, the exception object |
| 467 | will have one extra attribute called :attr:`child_traceback`, which is a string |
Georg Brandl | 8167561 | 2010-08-26 14:30:56 +0000 | [diff] [blame] | 468 | containing traceback information from the child's point of view. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 469 | |
| 470 | The most common exception raised is :exc:`OSError`. This occurs, for example, |
| 471 | when trying to execute a non-existent file. Applications should prepare for |
| 472 | :exc:`OSError` exceptions. |
| 473 | |
| 474 | A :exc:`ValueError` will be raised if :class:`Popen` is called with invalid |
| 475 | arguments. |
| 476 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 477 | :func:`check_call` and :func:`check_output` will raise |
| 478 | :exc:`CalledProcessError` if the called process returns a non-zero return |
| 479 | code. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 480 | |
| 481 | |
| 482 | Security |
| 483 | ^^^^^^^^ |
| 484 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 485 | Unlike some other popen functions, this implementation will never call a |
| 486 | system shell implicitly. This means that all characters, including shell |
| 487 | metacharacters, can safely be passed to child processes. Obviously, if the |
| 488 | shell is invoked explicitly, then it is the application's responsibility to |
| 489 | ensure that all whitespace and metacharacters are quoted appropriately. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 490 | |
| 491 | |
| 492 | Popen Objects |
| 493 | ------------- |
| 494 | |
| 495 | Instances of the :class:`Popen` class have the following methods: |
| 496 | |
| 497 | |
| 498 | .. method:: Popen.poll() |
| 499 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 500 | Check if child process has terminated. Set and return :attr:`returncode` |
| 501 | attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 502 | |
| 503 | |
| 504 | .. method:: Popen.wait() |
| 505 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 506 | Wait for child process to terminate. Set and return :attr:`returncode` |
| 507 | attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 508 | |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 509 | .. warning:: |
| 510 | |
Philip Jenvey | b089684 | 2009-12-03 02:29:36 +0000 | [diff] [blame] | 511 | This will deadlock when using ``stdout=PIPE`` and/or |
| 512 | ``stderr=PIPE`` and the child process generates enough output to |
| 513 | a pipe such that it blocks waiting for the OS pipe buffer to |
| 514 | accept more data. Use :meth:`communicate` to avoid that. |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 515 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 516 | |
| 517 | .. method:: Popen.communicate(input=None) |
| 518 | |
| 519 | Interact with process: Send data to stdin. Read data from stdout and stderr, |
| 520 | until end-of-file is reached. Wait for process to terminate. The optional |
Georg Brandl | e11787a | 2008-07-01 19:10:52 +0000 | [diff] [blame] | 521 | *input* argument should be a byte string to be sent to the child process, or |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 522 | ``None``, if no data should be sent to the child. |
| 523 | |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 524 | :meth:`communicate` returns a tuple ``(stdoutdata, stderrdata)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 525 | |
Guido van Rossum | 0d3fb8a | 2007-11-26 23:23:18 +0000 | [diff] [blame] | 526 | Note that if you want to send data to the process's stdin, you need to create |
| 527 | the Popen object with ``stdin=PIPE``. Similarly, to get anything other than |
| 528 | ``None`` in the result tuple, you need to give ``stdout=PIPE`` and/or |
| 529 | ``stderr=PIPE`` too. |
| 530 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 531 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 532 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 533 | The data read is buffered in memory, so do not use this method if the data |
| 534 | size is large or unlimited. |
| 535 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 536 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 537 | .. method:: Popen.send_signal(signal) |
| 538 | |
| 539 | Sends the signal *signal* to the child. |
| 540 | |
| 541 | .. note:: |
| 542 | |
Brian Curtin | eb24d74 | 2010-04-12 17:16:38 +0000 | [diff] [blame] | 543 | On Windows, SIGTERM is an alias for :meth:`terminate`. CTRL_C_EVENT and |
Senthil Kumaran | 916bd38 | 2010-10-15 12:55:19 +0000 | [diff] [blame] | 544 | CTRL_BREAK_EVENT can be sent to processes started with a *creationflags* |
Brian Curtin | eb24d74 | 2010-04-12 17:16:38 +0000 | [diff] [blame] | 545 | parameter which includes `CREATE_NEW_PROCESS_GROUP`. |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 546 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 547 | |
| 548 | .. method:: Popen.terminate() |
| 549 | |
| 550 | Stop the child. On Posix OSs the method sends SIGTERM to the |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 551 | child. On Windows the Win32 API function :c:func:`TerminateProcess` is called |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 552 | to stop the child. |
| 553 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 554 | |
| 555 | .. method:: Popen.kill() |
| 556 | |
| 557 | Kills the child. On Posix OSs the function sends SIGKILL to the child. |
| 558 | On Windows :meth:`kill` is an alias for :meth:`terminate`. |
| 559 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 560 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 561 | The following attributes are also available: |
| 562 | |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 563 | .. warning:: |
| 564 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 565 | Use :meth:`communicate` rather than :attr:`.stdin.write <stdin>`, |
| 566 | :attr:`.stdout.read <stdout>` or :attr:`.stderr.read <stderr>` to avoid |
| 567 | deadlocks due to any of the other OS pipe buffers filling up and blocking the |
| 568 | child process. |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 569 | |
| 570 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 571 | .. attribute:: Popen.stdin |
| 572 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 573 | If the *stdin* argument was :data:`PIPE`, this attribute is a :term:`file |
| 574 | object` that provides input to the child process. Otherwise, it is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 575 | |
| 576 | |
| 577 | .. attribute:: Popen.stdout |
| 578 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 579 | If the *stdout* argument was :data:`PIPE`, this attribute is a :term:`file |
| 580 | object` that provides output from the child process. Otherwise, it is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 581 | |
| 582 | |
| 583 | .. attribute:: Popen.stderr |
| 584 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 585 | If the *stderr* argument was :data:`PIPE`, this attribute is a :term:`file |
| 586 | object` that provides error output from the child process. Otherwise, it is |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 587 | ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 588 | |
| 589 | |
| 590 | .. attribute:: Popen.pid |
| 591 | |
| 592 | The process ID of the child process. |
| 593 | |
Georg Brandl | 58bfdca | 2010-03-21 09:50:49 +0000 | [diff] [blame] | 594 | Note that if you set the *shell* argument to ``True``, this is the process ID |
| 595 | of the spawned shell. |
| 596 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 597 | |
| 598 | .. attribute:: Popen.returncode |
| 599 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 600 | The child return code, set by :meth:`poll` and :meth:`wait` (and indirectly |
| 601 | by :meth:`communicate`). A ``None`` value indicates that the process |
| 602 | hasn't terminated yet. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 603 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 604 | A negative value ``-N`` indicates that the child was terminated by signal |
| 605 | ``N`` (Unix only). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 606 | |
| 607 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 608 | Windows Popen Helpers |
| 609 | --------------------- |
| 610 | |
| 611 | The :class:`STARTUPINFO` class and following constants are only available |
| 612 | on Windows. |
| 613 | |
| 614 | .. class:: STARTUPINFO() |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 615 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 616 | Partial support of the Windows |
| 617 | `STARTUPINFO <http://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx>`__ |
| 618 | structure is used for :class:`Popen` creation. |
| 619 | |
| 620 | .. attribute:: dwFlags |
| 621 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 622 | A bit field that determines whether certain :class:`STARTUPINFO` |
| 623 | attributes are used when the process creates a window. :: |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 624 | |
| 625 | si = subprocess.STARTUPINFO() |
| 626 | si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW |
| 627 | |
| 628 | .. attribute:: hStdInput |
| 629 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 630 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 631 | is the standard input handle for the process. If |
| 632 | :data:`STARTF_USESTDHANDLES` is not specified, the default for standard |
| 633 | input is the keyboard buffer. |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 634 | |
| 635 | .. attribute:: hStdOutput |
| 636 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 637 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 638 | is the standard output handle for the process. Otherwise, this attribute |
| 639 | is ignored and the default for standard output is the console window's |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 640 | buffer. |
| 641 | |
| 642 | .. attribute:: hStdError |
| 643 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 644 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 645 | is the standard error handle for the process. Otherwise, this attribute is |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 646 | ignored and the default for standard error is the console window's buffer. |
| 647 | |
| 648 | .. attribute:: wShowWindow |
| 649 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 650 | If :attr:`dwFlags` specifies :data:`STARTF_USESHOWWINDOW`, this attribute |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 651 | can be any of the values that can be specified in the ``nCmdShow`` |
| 652 | parameter for the |
| 653 | `ShowWindow <http://msdn.microsoft.com/en-us/library/ms633548(v=vs.85).aspx>`__ |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 654 | function, except for ``SW_SHOWDEFAULT``. Otherwise, this attribute is |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 655 | ignored. |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 656 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 657 | :data:`SW_HIDE` is provided for this attribute. It is used when |
| 658 | :class:`Popen` is called with ``shell=True``. |
| 659 | |
| 660 | |
| 661 | Constants |
| 662 | ^^^^^^^^^ |
| 663 | |
| 664 | The :mod:`subprocess` module exposes the following constants. |
| 665 | |
| 666 | .. data:: STD_INPUT_HANDLE |
| 667 | |
| 668 | The standard input device. Initially, this is the console input buffer, |
| 669 | ``CONIN$``. |
| 670 | |
| 671 | .. data:: STD_OUTPUT_HANDLE |
| 672 | |
| 673 | The standard output device. Initially, this is the active console screen |
| 674 | buffer, ``CONOUT$``. |
| 675 | |
| 676 | .. data:: STD_ERROR_HANDLE |
| 677 | |
| 678 | The standard error device. Initially, this is the active console screen |
| 679 | buffer, ``CONOUT$``. |
| 680 | |
| 681 | .. data:: SW_HIDE |
| 682 | |
| 683 | Hides the window. Another window will be activated. |
| 684 | |
| 685 | .. data:: STARTF_USESTDHANDLES |
| 686 | |
| 687 | Specifies that the :attr:`STARTUPINFO.hStdInput`, |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 688 | :attr:`STARTUPINFO.hStdOutput`, and :attr:`STARTUPINFO.hStdError` attributes |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 689 | contain additional information. |
| 690 | |
| 691 | .. data:: STARTF_USESHOWWINDOW |
| 692 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 693 | Specifies that the :attr:`STARTUPINFO.wShowWindow` attribute contains |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 694 | additional information. |
| 695 | |
| 696 | .. data:: CREATE_NEW_CONSOLE |
| 697 | |
| 698 | The new process has a new console, instead of inheriting its parent's |
| 699 | console (the default). |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 700 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 701 | This flag is always set when :class:`Popen` is created with ``shell=True``. |
| 702 | |
Brian Curtin | 3040193 | 2011-04-29 22:20:57 -0500 | [diff] [blame] | 703 | .. data:: CREATE_NEW_PROCESS_GROUP |
| 704 | |
| 705 | A :class:`Popen` ``creationflags`` parameter to specify that a new process |
| 706 | group will be created. This flag is necessary for using :func:`os.kill` |
| 707 | on the subprocess. |
| 708 | |
| 709 | This flag is ignored if :data:`CREATE_NEW_CONSOLE` is specified. |
| 710 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 711 | |
Benjamin Peterson | dcf97b9 | 2008-07-02 17:30:14 +0000 | [diff] [blame] | 712 | .. _subprocess-replacements: |
| 713 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 714 | Replacing Older Functions with the subprocess Module |
| 715 | ---------------------------------------------------- |
| 716 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 717 | In this section, "a becomes b" means that b can be used as a replacement for a. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 718 | |
| 719 | .. note:: |
| 720 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 721 | All "a" functions in this section fail (more or less) silently if the |
| 722 | executed program cannot be found; the "b" replacements raise :exc:`OSError` |
| 723 | instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 724 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 725 | In addition, the replacements using :func:`check_output` will fail with a |
| 726 | :exc:`CalledProcessError` if the requested operation produces a non-zero |
| 727 | return code. The output is still available as the ``output`` attribute of |
| 728 | the raised exception. |
| 729 | |
| 730 | In the following examples, we assume that the relevant functions have already |
| 731 | been imported from the subprocess module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 732 | |
| 733 | |
| 734 | Replacing /bin/sh shell backquote |
| 735 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 736 | |
| 737 | :: |
| 738 | |
| 739 | output=`mycmd myarg` |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 740 | # becomes |
| 741 | output = check_output(["mycmd", "myarg"]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 742 | |
| 743 | |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 744 | Replacing shell pipeline |
| 745 | ^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 746 | |
| 747 | :: |
| 748 | |
| 749 | output=`dmesg | grep hda` |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 750 | # becomes |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 751 | p1 = Popen(["dmesg"], stdout=PIPE) |
| 752 | p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE) |
Gregory P. Smith | e09d2f1 | 2011-02-05 21:47:25 +0000 | [diff] [blame] | 753 | p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 754 | output = p2.communicate()[0] |
| 755 | |
Gregory P. Smith | e09d2f1 | 2011-02-05 21:47:25 +0000 | [diff] [blame] | 756 | The p1.stdout.close() call after starting the p2 is important in order for p1 |
| 757 | to receive a SIGPIPE if p2 exits before p1. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 758 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 759 | Alternatively, for trusted input, the shell's own pipeline support may still |
R David Murray | 28b8b94 | 2012-04-03 08:46:48 -0400 | [diff] [blame] | 760 | be used directly:: |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 761 | |
| 762 | output=`dmesg | grep hda` |
| 763 | # becomes |
| 764 | output=check_output("dmesg | grep hda", shell=True) |
| 765 | |
| 766 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 767 | Replacing :func:`os.system` |
| 768 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 769 | |
| 770 | :: |
| 771 | |
| 772 | sts = os.system("mycmd" + " myarg") |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 773 | # becomes |
| 774 | sts = call("mycmd" + " myarg", shell=True) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 775 | |
| 776 | Notes: |
| 777 | |
| 778 | * Calling the program through the shell is usually not required. |
| 779 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 780 | A more realistic example would look like this:: |
| 781 | |
| 782 | try: |
| 783 | retcode = call("mycmd" + " myarg", shell=True) |
| 784 | if retcode < 0: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 785 | print("Child was terminated by signal", -retcode, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 786 | else: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 787 | print("Child returned", retcode, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 788 | except OSError as e: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 789 | print("Execution failed:", e, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 790 | |
| 791 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 792 | Replacing the :func:`os.spawn <os.spawnl>` family |
| 793 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 794 | |
| 795 | P_NOWAIT example:: |
| 796 | |
| 797 | pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg") |
| 798 | ==> |
| 799 | pid = Popen(["/bin/mycmd", "myarg"]).pid |
| 800 | |
| 801 | P_WAIT example:: |
| 802 | |
| 803 | retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg") |
| 804 | ==> |
| 805 | retcode = call(["/bin/mycmd", "myarg"]) |
| 806 | |
| 807 | Vector example:: |
| 808 | |
| 809 | os.spawnvp(os.P_NOWAIT, path, args) |
| 810 | ==> |
| 811 | Popen([path] + args[1:]) |
| 812 | |
| 813 | Environment example:: |
| 814 | |
| 815 | os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env) |
| 816 | ==> |
| 817 | Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"}) |
| 818 | |
| 819 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 820 | |
| 821 | Replacing :func:`os.popen`, :func:`os.popen2`, :func:`os.popen3` |
| 822 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 823 | |
| 824 | :: |
| 825 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 826 | (child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 827 | ==> |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 828 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 829 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 830 | (child_stdin, child_stdout) = (p.stdin, p.stdout) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 831 | |
| 832 | :: |
| 833 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 834 | (child_stdin, |
| 835 | child_stdout, |
| 836 | child_stderr) = os.popen3(cmd, mode, bufsize) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 837 | ==> |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 838 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 839 | stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True) |
| 840 | (child_stdin, |
| 841 | child_stdout, |
| 842 | child_stderr) = (p.stdin, p.stdout, p.stderr) |
| 843 | |
| 844 | :: |
| 845 | |
| 846 | (child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize) |
| 847 | ==> |
| 848 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 849 | stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True) |
| 850 | (child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout) |
| 851 | |
| 852 | Return code handling translates as follows:: |
| 853 | |
| 854 | pipe = os.popen(cmd, 'w') |
| 855 | ... |
| 856 | rc = pipe.close() |
Stefan Krah | fc9e08d | 2010-07-14 10:16:11 +0000 | [diff] [blame] | 857 | if rc is not None and rc >> 8: |
Ezio Melotti | 985e24d | 2009-09-13 07:54:02 +0000 | [diff] [blame] | 858 | print("There were some errors") |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 859 | ==> |
| 860 | process = Popen(cmd, 'w', stdin=PIPE) |
| 861 | ... |
| 862 | process.stdin.close() |
| 863 | if process.wait() != 0: |
Ezio Melotti | 985e24d | 2009-09-13 07:54:02 +0000 | [diff] [blame] | 864 | print("There were some errors") |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 865 | |
| 866 | |
| 867 | Replacing functions from the :mod:`popen2` module |
| 868 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 869 | |
| 870 | .. note:: |
| 871 | |
| 872 | If the cmd argument to popen2 functions is a string, the command is executed |
| 873 | through /bin/sh. If it is a list, the command is directly executed. |
| 874 | |
| 875 | :: |
| 876 | |
| 877 | (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode) |
| 878 | ==> |
| 879 | p = Popen(["somestring"], shell=True, bufsize=bufsize, |
| 880 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 881 | (child_stdout, child_stdin) = (p.stdout, p.stdin) |
| 882 | |
| 883 | :: |
| 884 | |
| 885 | (child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, mode) |
| 886 | ==> |
| 887 | p = Popen(["mycmd", "myarg"], bufsize=bufsize, |
| 888 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 889 | (child_stdout, child_stdin) = (p.stdout, p.stdin) |
| 890 | |
| 891 | :class:`popen2.Popen3` and :class:`popen2.Popen4` basically work as |
| 892 | :class:`subprocess.Popen`, except that: |
| 893 | |
| 894 | * :class:`Popen` raises an exception if the execution fails. |
| 895 | |
| 896 | * the *capturestderr* argument is replaced with the *stderr* argument. |
| 897 | |
| 898 | * ``stdin=PIPE`` and ``stdout=PIPE`` must be specified. |
| 899 | |
| 900 | * popen2 closes all file descriptors by default, but you have to specify |
Gregory P. Smith | f560485 | 2010-12-13 06:45:02 +0000 | [diff] [blame] | 901 | ``close_fds=True`` with :class:`Popen` to guarantee this behavior on |
| 902 | all platforms or past Python versions. |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 903 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 904 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 905 | Legacy Shell Invocation Functions |
Nick Coghlan | 32e4a58 | 2011-11-08 21:50:58 +1000 | [diff] [blame] | 906 | --------------------------------- |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 907 | |
| 908 | This module also provides the following legacy functions from the 2.x |
| 909 | ``commands`` module. These operations implicitly invoke the system shell and |
| 910 | none of the guarantees described above regarding security and exception |
| 911 | handling consistency are valid for these functions. |
| 912 | |
| 913 | .. function:: getstatusoutput(cmd) |
| 914 | |
| 915 | Return ``(status, output)`` of executing *cmd* in a shell. |
| 916 | |
| 917 | Execute the string *cmd* in a shell with :func:`os.popen` and return a 2-tuple |
| 918 | ``(status, output)``. *cmd* is actually run as ``{ cmd ; } 2>&1``, so that the |
| 919 | returned output will contain output or error messages. A trailing newline is |
| 920 | stripped from the output. The exit status for the command can be interpreted |
| 921 | according to the rules for the C function :c:func:`wait`. Example:: |
| 922 | |
| 923 | >>> subprocess.getstatusoutput('ls /bin/ls') |
| 924 | (0, '/bin/ls') |
| 925 | >>> subprocess.getstatusoutput('cat /bin/junk') |
| 926 | (256, 'cat: /bin/junk: No such file or directory') |
| 927 | >>> subprocess.getstatusoutput('/bin/junk') |
| 928 | (256, 'sh: /bin/junk: not found') |
| 929 | |
| 930 | Availability: UNIX. |
| 931 | |
| 932 | |
| 933 | .. function:: getoutput(cmd) |
| 934 | |
| 935 | Return output (stdout and stderr) of executing *cmd* in a shell. |
| 936 | |
| 937 | Like :func:`getstatusoutput`, except the exit status is ignored and the return |
| 938 | value is a string containing the command's output. Example:: |
| 939 | |
| 940 | >>> subprocess.getoutput('ls /bin/ls') |
| 941 | '/bin/ls' |
| 942 | |
| 943 | Availability: UNIX. |
| 944 | |
Nick Coghlan | 32e4a58 | 2011-11-08 21:50:58 +1000 | [diff] [blame] | 945 | |
| 946 | Notes |
| 947 | ----- |
| 948 | |
| 949 | .. _converting-argument-sequence: |
| 950 | |
| 951 | Converting an argument sequence to a string on Windows |
| 952 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 953 | |
| 954 | On Windows, an *args* sequence is converted to a string that can be parsed |
| 955 | using the following rules (which correspond to the rules used by the MS C |
| 956 | runtime): |
| 957 | |
| 958 | 1. Arguments are delimited by white space, which is either a |
| 959 | space or a tab. |
| 960 | |
| 961 | 2. A string surrounded by double quotation marks is |
| 962 | interpreted as a single argument, regardless of white space |
| 963 | contained within. A quoted string can be embedded in an |
| 964 | argument. |
| 965 | |
| 966 | 3. A double quotation mark preceded by a backslash is |
| 967 | interpreted as a literal double quotation mark. |
| 968 | |
| 969 | 4. Backslashes are interpreted literally, unless they |
| 970 | immediately precede a double quotation mark. |
| 971 | |
| 972 | 5. If backslashes immediately precede a double quotation mark, |
| 973 | every pair of backslashes is interpreted as a literal |
| 974 | backslash. If the number of backslashes is odd, the last |
| 975 | backslash escapes the next double quotation mark as |
| 976 | described in rule 3. |