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 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 33 | .. function:: call(args, *, stdin=None, stdout=None, stderr=None, shell=False, timeout=None) |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 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 |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 39 | in :ref:`frequently-used-arguments` (hence the use of keyword-only notation |
| 40 | in the abbreviated signature). The full function signature is largely the |
| 41 | same as that of the :class:`Popen` constructor - this function passes all |
| 42 | supplied arguments other than *timeout* directly through to that interface. |
| 43 | |
| 44 | The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout |
| 45 | expires, the child process will be killed and then waited for again. The |
| 46 | :exc:`TimeoutExpired` exception will be re-raised after the child process |
| 47 | has terminated. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 48 | |
| 49 | Examples:: |
| 50 | |
| 51 | >>> subprocess.call(["ls", "-l"]) |
| 52 | 0 |
| 53 | |
| 54 | >>> subprocess.call("exit 1", shell=True) |
| 55 | 1 |
| 56 | |
| 57 | .. warning:: |
| 58 | |
| 59 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 60 | if combined with untrusted input. See the warning under |
| 61 | :ref:`frequently-used-arguments` for details. |
| 62 | |
| 63 | .. note:: |
| 64 | |
| 65 | Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As |
| 66 | the pipes are not being read in the current process, the child |
| 67 | process may block if it generates enough output to a pipe to fill up |
| 68 | the OS pipe buffer. |
| 69 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 70 | .. versionchanged:: 3.3 |
| 71 | *timeout* was added. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 72 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 73 | |
| 74 | .. function:: check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, timeout=None) |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 75 | |
| 76 | Run command with arguments. Wait for command to complete. If the return |
| 77 | code was zero then return, otherwise raise :exc:`CalledProcessError`. The |
| 78 | :exc:`CalledProcessError` object will have the return code in the |
| 79 | :attr:`returncode` attribute. |
| 80 | |
| 81 | The arguments shown above are merely the most common ones, described below |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 82 | in :ref:`frequently-used-arguments` (hence the use of keyword-only notation |
| 83 | in the abbreviated signature). The full function signature is largely the |
| 84 | same as that of the :class:`Popen` constructor - this function passes all |
| 85 | supplied arguments other than *timeout* directly through to that interface. |
| 86 | |
| 87 | The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout |
| 88 | expires, the child process will be killed and then waited for again. The |
| 89 | :exc:`TimeoutExpired` exception will be re-raised after the child process |
| 90 | has terminated. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 91 | |
| 92 | Examples:: |
| 93 | |
| 94 | >>> subprocess.check_call(["ls", "-l"]) |
| 95 | 0 |
| 96 | |
| 97 | >>> subprocess.check_call("exit 1", shell=True) |
| 98 | Traceback (most recent call last): |
| 99 | ... |
| 100 | subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 |
| 101 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 102 | .. warning:: |
| 103 | |
| 104 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 105 | if combined with untrusted input. See the warning under |
| 106 | :ref:`frequently-used-arguments` for details. |
| 107 | |
| 108 | .. note:: |
| 109 | |
| 110 | Do not use ``stdout=PIPE`` or ``stderr=PIPE`` with this function. As |
| 111 | the pipes are not being read in the current process, the child |
| 112 | process may block if it generates enough output to a pipe to fill up |
| 113 | the OS pipe buffer. |
| 114 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 115 | .. versionchanged:: 3.3 |
| 116 | *timeout* was added. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 117 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 118 | |
| 119 | .. function:: check_output(args, *, stdin=None, stderr=None, shell=False, universal_newlines=False, timeout=None) |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 120 | |
| 121 | Run command with arguments and return its output as a byte string. |
| 122 | |
| 123 | If the return code was non-zero it raises a :exc:`CalledProcessError`. The |
| 124 | :exc:`CalledProcessError` object will have the return code in the |
| 125 | :attr:`returncode` attribute and any output in the :attr:`output` |
| 126 | attribute. |
| 127 | |
| 128 | The arguments shown above are merely the most common ones, described below |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 129 | in :ref:`frequently-used-arguments` (hence the use of keyword-only notation |
| 130 | in the abbreviated signature). The full function signature is largely the |
| 131 | same as that of the :class:`Popen` constructor - this functions passes all |
| 132 | supplied arguments other than *timeout* directly through to that interface. |
| 133 | In addition, *stdout* is not permitted as an argument, as it is used |
| 134 | internally to collect the output from the subprocess. |
| 135 | |
| 136 | The *timeout* argument is passed to :meth:`Popen.wait`. If the timeout |
| 137 | expires, the child process will be killed and then waited for again. The |
| 138 | :exc:`TimeoutExpired` exception will be re-raised after the child process |
| 139 | has terminated. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 140 | |
| 141 | Examples:: |
| 142 | |
| 143 | >>> subprocess.check_output(["echo", "Hello World!"]) |
| 144 | b'Hello World!\n' |
| 145 | |
| 146 | >>> subprocess.check_output(["echo", "Hello World!"], universal_newlines=True) |
| 147 | 'Hello World!\n' |
| 148 | |
| 149 | >>> subprocess.check_output("exit 1", shell=True) |
| 150 | Traceback (most recent call last): |
| 151 | ... |
| 152 | subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1 |
| 153 | |
| 154 | By default, this function will return the data as encoded bytes. The actual |
| 155 | encoding of the output data may depend on the command being invoked, so the |
| 156 | decoding to text will often need to be handled at the application level. |
| 157 | |
| 158 | This behaviour may be overridden by setting *universal_newlines* to |
| 159 | :const:`True` as described below in :ref:`frequently-used-arguments`. |
| 160 | |
| 161 | To also capture standard error in the result, use |
| 162 | ``stderr=subprocess.STDOUT``:: |
| 163 | |
| 164 | >>> subprocess.check_output( |
| 165 | ... "ls non_existent_file; exit 0", |
| 166 | ... stderr=subprocess.STDOUT, |
| 167 | ... shell=True) |
| 168 | 'ls: non_existent_file: No such file or directory\n' |
| 169 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 170 | .. versionadded:: 3.1 |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 171 | |
| 172 | .. warning:: |
| 173 | |
| 174 | Invoking the system shell with ``shell=True`` can be a security hazard |
| 175 | if combined with untrusted input. See the warning under |
| 176 | :ref:`frequently-used-arguments` for details. |
| 177 | |
| 178 | .. note:: |
| 179 | |
| 180 | Do not use ``stderr=PIPE`` with this function. As the pipe is not being |
| 181 | read in the current process, the child process may block if it |
| 182 | generates enough output to the pipe to fill up the OS pipe buffer. |
| 183 | |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 184 | .. versionchanged:: 3.3 |
| 185 | *timeout* was added. |
| 186 | |
| 187 | |
| 188 | .. data:: DEVNULL |
| 189 | |
| 190 | Special value that can be used as the *stdin*, *stdout* or *stderr* argument |
| 191 | to :class:`Popen` and indicates that the special file :data:`os.devnull` |
| 192 | will be used. |
| 193 | |
| 194 | .. versionadded:: 3.3 |
| 195 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 196 | |
| 197 | .. data:: PIPE |
| 198 | |
| 199 | Special value that can be used as the *stdin*, *stdout* or *stderr* argument |
| 200 | to :class:`Popen` and indicates that a pipe to the standard stream should be |
| 201 | opened. |
| 202 | |
| 203 | |
| 204 | .. data:: STDOUT |
| 205 | |
| 206 | Special value that can be used as the *stderr* argument to :class:`Popen` and |
| 207 | indicates that standard error should go into the same handle as standard |
| 208 | output. |
| 209 | |
| 210 | |
| 211 | .. _frequently-used-arguments: |
| 212 | |
| 213 | Frequently Used Arguments |
| 214 | ^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 215 | |
| 216 | To support a wide variety of use cases, the :class:`Popen` constructor (and |
| 217 | the convenience functions) accept a large number of optional arguments. For |
| 218 | most typical use cases, many of these arguments can be safely left at their |
| 219 | default values. The arguments that are most commonly needed are: |
| 220 | |
| 221 | *args* is required for all calls and should be a string, or a sequence of |
| 222 | program arguments. Providing a sequence of arguments is generally |
| 223 | preferred, as it allows the module to take care of any required escaping |
| 224 | and quoting of arguments (e.g. to permit spaces in file names). If passing |
| 225 | a single string, either *shell* must be :const:`True` (see below) or else |
| 226 | the string must simply name the program to be executed without specifying |
| 227 | any arguments. |
| 228 | |
| 229 | *stdin*, *stdout* and *stderr* specify the executed program's standard input, |
| 230 | standard output and standard error file handles, respectively. Valid values |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 231 | are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive |
| 232 | integer), an existing file object, and ``None``. :data:`PIPE` indicates |
| 233 | that a new pipe to the child should be created. :data:`DEVNULL` indicates |
| 234 | that the special file :data:`os.devnull` will be used. With the default |
| 235 | settings of ``None``, no redirection will occur; the child's file handles |
| 236 | will be inherited from the parent. Additionally, *stderr* can be |
| 237 | :data:`STDOUT`, which indicates that the stderr data from the child |
| 238 | process should be captured into the same file handle as for *stdout*. |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 239 | |
| 240 | When *stdout* or *stderr* are pipes and *universal_newlines* is |
| 241 | :const:`True` then the output data is assumed to be encoded as UTF-8 and |
| 242 | will automatically be decoded to text. All line endings will be converted |
| 243 | to ``'\n'`` as described for the universal newlines `'U'`` mode argument |
| 244 | to :func:`open`. |
| 245 | |
| 246 | If *shell* is :const:`True`, the specified command will be executed through |
| 247 | the shell. This can be useful if you are using Python primarily for the |
| 248 | enhanced control flow it offers over most system shells and still want |
| 249 | access to other shell features such as filename wildcards, shell pipes and |
| 250 | environment variable expansion. |
| 251 | |
| 252 | .. warning:: |
| 253 | |
| 254 | Executing shell commands that incorporate unsanitized input from an |
| 255 | untrusted source makes a program vulnerable to `shell injection |
| 256 | <http://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_, |
| 257 | a serious security flaw which can result in arbitrary command execution. |
| 258 | For this reason, the use of *shell=True* is **strongly discouraged** in cases |
| 259 | where the command string is constructed from external input:: |
| 260 | |
| 261 | >>> from subprocess import call |
| 262 | >>> filename = input("What file would you like to display?\n") |
| 263 | What file would you like to display? |
| 264 | non_existent; rm -rf / # |
| 265 | >>> call("cat " + filename, shell=True) # Uh-oh. This will end badly... |
| 266 | |
| 267 | ``shell=False`` disables all shell based features, but does not suffer |
| 268 | from this vulnerability; see the Note in the :class:`Popen` constructor |
| 269 | documentation for helpful hints in getting ``shell=False`` to work. |
| 270 | |
| 271 | These options, along with all of the other options, are described in more |
| 272 | detail in the :class:`Popen` constructor documentation. |
| 273 | |
| 274 | |
| 275 | Popen Constuctor |
| 276 | ^^^^^^^^^^^^^^^^ |
| 277 | |
| 278 | The underlying process creation and management in this module is handled by |
| 279 | the :class:`Popen` class. It offers a lot of flexibility so that developers |
| 280 | are able to handle the less common cases not covered by the convenience |
| 281 | functions. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 282 | |
| 283 | |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 284 | .. 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] | 285 | |
| 286 | Arguments are: |
| 287 | |
Benjamin Peterson | d18de0e | 2008-07-31 20:21:46 +0000 | [diff] [blame] | 288 | *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] | 289 | to execute is normally the first item in the args sequence or the string if |
| 290 | a string is given, but can be explicitly set by using the *executable* |
| 291 | argument. When *executable* is given, the first item in the args sequence |
| 292 | is still treated by most programs as the command name, which can then be |
| 293 | different from the actual executable name. On Unix, it becomes the display |
| 294 | name for the executing program in utilities such as :program:`ps`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 295 | |
| 296 | 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] | 297 | :meth:`os.execvp` like behavior to execute the child program. |
| 298 | *args* should normally be a |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 299 | sequence. If a string is specified for *args*, it will be used as the name |
| 300 | or path of the program to execute; this will only work if the program is |
| 301 | being given no arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 302 | |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 303 | .. note:: |
| 304 | |
| 305 | :meth:`shlex.split` can be useful when determining the correct |
| 306 | tokenization for *args*, especially in complex cases:: |
| 307 | |
| 308 | >>> import shlex, subprocess |
R. David Murray | 73bc75b | 2010-02-05 16:25:12 +0000 | [diff] [blame] | 309 | >>> command_line = input() |
R. David Murray | 5973e4d | 2010-02-04 16:41:57 +0000 | [diff] [blame] | 310 | /bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'" |
| 311 | >>> args = shlex.split(command_line) |
| 312 | >>> print(args) |
| 313 | ['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"] |
| 314 | >>> p = subprocess.Popen(args) # Success! |
| 315 | |
| 316 | Note in particular that options (such as *-input*) and arguments (such |
| 317 | as *eggs.txt*) that are separated by whitespace in the shell go in separate |
| 318 | list elements, while arguments that need quoting or backslash escaping when |
| 319 | used in the shell (such as filenames containing spaces or the *echo* command |
| 320 | shown above) are single list elements. |
| 321 | |
| 322 | On Unix, with *shell=True*: If args is a string, it specifies the command |
| 323 | string to execute through the shell. This means that the string must be |
| 324 | formatted exactly as it would be when typed at the shell prompt. This |
| 325 | includes, for example, quoting or backslash escaping filenames with spaces in |
| 326 | them. If *args* is a sequence, the first item specifies the command string, and |
| 327 | any additional items will be treated as additional arguments to the shell |
| 328 | itself. That is to say, *Popen* does the equivalent of:: |
| 329 | |
| 330 | Popen(['/bin/sh', '-c', args[0], args[1], ...]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 331 | |
R. David Murray | c7399d0 | 2010-11-12 00:35:31 +0000 | [diff] [blame] | 332 | .. warning:: |
| 333 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 334 | Enabling this option can be a security hazard if combined with untrusted |
| 335 | input. See the warning under :ref:`frequently-used-arguments` |
| 336 | for details. |
R. David Murray | c7399d0 | 2010-11-12 00:35:31 +0000 | [diff] [blame] | 337 | |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 338 | On Windows: the :class:`Popen` class uses CreateProcess() to execute the |
| 339 | child program, which operates on strings. If *args* is a sequence, it will |
| 340 | be converted to a string in a manner described in |
| 341 | :ref:`converting-argument-sequence`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 342 | |
| 343 | *bufsize*, if given, has the same meaning as the corresponding argument to the |
| 344 | built-in open() function: :const:`0` means unbuffered, :const:`1` means line |
| 345 | buffered, any other positive value means use a buffer of (approximately) that |
| 346 | size. A negative *bufsize* means to use the system default, which usually means |
| 347 | fully buffered. The default value for *bufsize* is :const:`0` (unbuffered). |
| 348 | |
Antoine Pitrou | 4b87620 | 2010-06-02 17:10:49 +0000 | [diff] [blame] | 349 | .. note:: |
| 350 | |
| 351 | If you experience performance issues, it is recommended that you try to |
| 352 | enable buffering by setting *bufsize* to either -1 or a large enough |
| 353 | positive value (such as 4096). |
| 354 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 355 | The *executable* argument specifies the program to execute. It is very seldom |
| 356 | needed: Usually, the program to execute is defined by the *args* argument. If |
| 357 | ``shell=True``, the *executable* argument specifies which shell to use. On Unix, |
| 358 | 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] | 359 | specified by the :envvar:`COMSPEC` environment variable. The only reason you |
| 360 | would need to specify ``shell=True`` on Windows is where the command you |
| 361 | wish to execute is actually built in to the shell, eg ``dir``, ``copy``. |
| 362 | You don't need ``shell=True`` to run a batch file, nor to run a console-based |
| 363 | executable. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 364 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 365 | *stdin*, *stdout* and *stderr* specify the executed program's standard input, |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 366 | standard output and standard error file handles, respectively. Valid values |
Ross Lagerwall | ba102ec | 2011-03-16 18:40:25 +0200 | [diff] [blame] | 367 | are :data:`PIPE`, :data:`DEVNULL`, an existing file descriptor (a positive |
| 368 | integer), an existing :term:`file object`, and ``None``. :data:`PIPE` |
| 369 | indicates that a new pipe to the child should be created. :data:`DEVNULL` |
Nick Coghlan | 217f05b | 2011-11-08 22:11:21 +1000 | [diff] [blame^] | 370 | indicates that the special file :data:`os.devnull` will be used. With the |
| 371 | default settings of ``None``, no redirection will occur; the child's file |
| 372 | handles will be inherited from the parent. Additionally, *stderr* can be |
| 373 | :data:`STDOUT`, which indicates that the stderr data from the applications |
| 374 | should be captured into the same file handle as for stdout. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 375 | |
| 376 | 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] | 377 | child process just before the child is executed. |
| 378 | (Unix only) |
| 379 | |
| 380 | .. warning:: |
| 381 | |
| 382 | The *preexec_fn* parameter is not safe to use in the presence of threads |
| 383 | in your application. The child process could deadlock before exec is |
| 384 | called. |
| 385 | If you must use it, keep it trivial! Minimize the number of libraries |
| 386 | you call into. |
| 387 | |
| 388 | .. note:: |
| 389 | |
| 390 | If you need to modify the environment for the child use the *env* |
| 391 | parameter rather than doing it in a *preexec_fn*. |
| 392 | The *start_new_session* parameter can take the place of a previously |
| 393 | common use of *preexec_fn* to call os.setsid() in the child. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 394 | |
| 395 | If *close_fds* is true, all file descriptors except :const:`0`, :const:`1` and |
| 396 | :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] | 397 | The default varies by platform: Always true on Unix. On Windows it is |
| 398 | true when *stdin*/*stdout*/*stderr* are :const:`None`, false otherwise. |
Gregory P. Smith | d23047b | 2010-12-04 09:10:44 +0000 | [diff] [blame] | 399 | 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] | 400 | child process. Note that on Windows, you cannot set *close_fds* to true and |
| 401 | also redirect the standard handles by setting *stdin*, *stdout* or *stderr*. |
| 402 | |
Gregory P. Smith | 8edd99d | 2010-12-14 13:43:30 +0000 | [diff] [blame] | 403 | .. versionchanged:: 3.2 |
| 404 | The default for *close_fds* was changed from :const:`False` to |
| 405 | what is described above. |
| 406 | |
| 407 | *pass_fds* is an optional sequence of file descriptors to keep open |
| 408 | between the parent and child. Providing any *pass_fds* forces |
| 409 | *close_fds* to be :const:`True`. (Unix only) |
| 410 | |
| 411 | .. versionadded:: 3.2 |
| 412 | The *pass_fds* parameter was added. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 413 | |
| 414 | If *cwd* is not ``None``, the child's current directory will be changed to *cwd* |
| 415 | before it is executed. Note that this directory is not considered when |
| 416 | searching the executable, so you can't specify the program's path relative to |
| 417 | *cwd*. |
| 418 | |
Gregory P. Smith | fb94c5f | 2010-03-14 06:49:55 +0000 | [diff] [blame] | 419 | If *restore_signals* is True (the default) all signals that Python has set to |
| 420 | SIG_IGN are restored to SIG_DFL in the child process before the exec. |
| 421 | Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. |
| 422 | (Unix only) |
| 423 | |
| 424 | .. versionchanged:: 3.2 |
| 425 | *restore_signals* was added. |
| 426 | |
| 427 | If *start_new_session* is True the setsid() system call will be made in the |
| 428 | child process prior to the execution of the subprocess. (Unix only) |
| 429 | |
| 430 | .. versionchanged:: 3.2 |
| 431 | *start_new_session* was added. |
| 432 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 433 | 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] | 434 | variables for the new process; these are used instead of the default |
| 435 | behavior of inheriting the current process' environment. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 436 | |
R. David Murray | 1055e89 | 2009-04-16 18:15:32 +0000 | [diff] [blame] | 437 | .. note:: |
R. David Murray | f4ac149 | 2009-04-15 22:35:15 +0000 | [diff] [blame] | 438 | |
Georg Brandl | 2708f3a | 2009-12-20 14:38:23 +0000 | [diff] [blame] | 439 | If specified, *env* must provide any variables required for the program to |
| 440 | execute. On Windows, in order to run a `side-by-side assembly`_ the |
| 441 | specified *env* **must** include a valid :envvar:`SystemRoot`. |
R. David Murray | f4ac149 | 2009-04-15 22:35:15 +0000 | [diff] [blame] | 442 | |
R. David Murray | 1055e89 | 2009-04-16 18:15:32 +0000 | [diff] [blame] | 443 | .. _side-by-side assembly: http://en.wikipedia.org/wiki/Side-by-Side_Assembly |
| 444 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 445 | If *universal_newlines* is :const:`True`, the file objects stdout and stderr are |
| 446 | opened as text files, but lines may be terminated by any of ``'\n'``, the Unix |
Georg Brandl | c575c90 | 2008-09-13 17:46:05 +0000 | [diff] [blame] | 447 | end-of-line convention, ``'\r'``, the old Macintosh convention or ``'\r\n'``, the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 448 | Windows convention. All of these external representations are seen as ``'\n'`` |
| 449 | by the Python program. |
| 450 | |
| 451 | .. note:: |
| 452 | |
Georg Brandl | 7f01a13 | 2009-09-16 15:58:14 +0000 | [diff] [blame] | 453 | This feature is only available if Python is built with universal newline |
| 454 | support (the default). Also, the newlines attribute of the file objects |
| 455 | :attr:`stdout`, :attr:`stdin` and :attr:`stderr` are not updated by the |
| 456 | :meth:`communicate` method. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 457 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 458 | If given, *startupinfo* will be a :class:`STARTUPINFO` object, which is |
| 459 | passed to the underlying ``CreateProcess`` function. |
Brian Curtin | 3040193 | 2011-04-29 22:20:57 -0500 | [diff] [blame] | 460 | *creationflags*, if given, can be :data:`CREATE_NEW_CONSOLE` or |
| 461 | :data:`CREATE_NEW_PROCESS_GROUP`. (Windows only) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 462 | |
Gregory P. Smith | 6b65745 | 2011-05-11 21:42:08 -0700 | [diff] [blame] | 463 | Popen objects are supported as context managers via the :keyword:`with` statement: |
| 464 | 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] | 465 | :: |
| 466 | |
| 467 | with Popen(["ifconfig"], stdout=PIPE) as proc: |
| 468 | log.write(proc.stdout.read()) |
| 469 | |
| 470 | .. versionchanged:: 3.2 |
| 471 | Added context manager support. |
| 472 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 473 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 474 | Exceptions |
| 475 | ^^^^^^^^^^ |
| 476 | |
| 477 | Exceptions raised in the child process, before the new program has started to |
| 478 | execute, will be re-raised in the parent. Additionally, the exception object |
| 479 | 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] | 480 | containing traceback information from the child's point of view. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 481 | |
| 482 | The most common exception raised is :exc:`OSError`. This occurs, for example, |
| 483 | when trying to execute a non-existent file. Applications should prepare for |
| 484 | :exc:`OSError` exceptions. |
| 485 | |
| 486 | A :exc:`ValueError` will be raised if :class:`Popen` is called with invalid |
| 487 | arguments. |
| 488 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 489 | :func:`check_call` and :func:`check_output` will raise |
| 490 | :exc:`CalledProcessError` if the called process returns a non-zero return |
| 491 | code. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 492 | |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 493 | All of the functions and methods that accept a *timeout* parameter, such as |
| 494 | :func:`call` and :meth:`Popen.communicate` will raise :exc:`TimeoutExpired` if |
| 495 | the timeout expires before the process exits. |
| 496 | |
Ronald Oussoren | c157790 | 2011-03-16 10:03:10 -0400 | [diff] [blame] | 497 | Exceptions defined in this module all inherit from :exc:`SubprocessError`. |
Gregory P. Smith | 54d412e | 2011-03-14 14:08:43 -0400 | [diff] [blame] | 498 | |
| 499 | .. versionadded:: 3.3 |
| 500 | The :exc:`SubprocessError` base class was added. |
| 501 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 502 | |
| 503 | Security |
| 504 | ^^^^^^^^ |
| 505 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 506 | Unlike some other popen functions, this implementation will never call a |
| 507 | system shell implicitly. This means that all characters, including shell |
| 508 | metacharacters, can safely be passed to child processes. Obviously, if the |
| 509 | shell is invoked explicitly, then it is the application's responsibility to |
| 510 | ensure that all whitespace and metacharacters are quoted appropriately. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 511 | |
| 512 | |
| 513 | Popen Objects |
| 514 | ------------- |
| 515 | |
| 516 | Instances of the :class:`Popen` class have the following methods: |
| 517 | |
| 518 | |
| 519 | .. method:: Popen.poll() |
| 520 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 521 | Check if child process has terminated. Set and return :attr:`returncode` |
| 522 | attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 523 | |
| 524 | |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 525 | .. method:: Popen.wait(timeout=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 526 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 527 | Wait for child process to terminate. Set and return :attr:`returncode` |
| 528 | attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 529 | |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 530 | If the process does not terminate after *timeout* seconds, raise a |
| 531 | :exc:`TimeoutExpired` exception. It is safe to catch this exception and |
| 532 | retry the wait. |
| 533 | |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 534 | .. warning:: |
| 535 | |
Philip Jenvey | b089684 | 2009-12-03 02:29:36 +0000 | [diff] [blame] | 536 | This will deadlock when using ``stdout=PIPE`` and/or |
| 537 | ``stderr=PIPE`` and the child process generates enough output to |
| 538 | a pipe such that it blocks waiting for the OS pipe buffer to |
| 539 | accept more data. Use :meth:`communicate` to avoid that. |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 540 | |
Reid Kleckner | 28f1303 | 2011-03-14 12:36:53 -0400 | [diff] [blame] | 541 | .. versionchanged:: 3.3 |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 542 | *timeout* was added. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 543 | |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 544 | |
| 545 | .. method:: Popen.communicate(input=None, timeout=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 546 | |
| 547 | Interact with process: Send data to stdin. Read data from stdout and stderr, |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 548 | until end-of-file is reached. Wait for process to terminate. The optional |
Gregory P. Smith | a454ef6 | 2011-05-22 22:29:49 -0700 | [diff] [blame] | 549 | *input* argument should be data to be sent to the child process, or |
| 550 | ``None``, if no data should be sent to the child. The type of *input* |
| 551 | must be bytes or, if *universal_newlines* was ``True``, a string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 552 | |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 553 | :meth:`communicate` returns a tuple ``(stdoutdata, stderrdata)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 554 | |
Guido van Rossum | 0d3fb8a | 2007-11-26 23:23:18 +0000 | [diff] [blame] | 555 | Note that if you want to send data to the process's stdin, you need to create |
| 556 | the Popen object with ``stdin=PIPE``. Similarly, to get anything other than |
| 557 | ``None`` in the result tuple, you need to give ``stdout=PIPE`` and/or |
| 558 | ``stderr=PIPE`` too. |
| 559 | |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 560 | If the process does not terminate after *timeout* seconds, a |
| 561 | :exc:`TimeoutExpired` exception will be raised. Catching this exception and |
| 562 | retrying communication will not lose any output. |
| 563 | |
| 564 | The child process is not killed if the timeout expires, so in order to |
| 565 | cleanup properly a well-behaved application should kill the child process and |
| 566 | finish communication:: |
| 567 | |
| 568 | proc = subprocess.Popen(...) |
| 569 | try: |
| 570 | outs, errs = proc.communicate(timeout=15) |
| 571 | except TimeoutExpired: |
| 572 | proc.kill() |
| 573 | outs, errs = proc.communicate() |
| 574 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 575 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 576 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 577 | The data read is buffered in memory, so do not use this method if the data |
| 578 | size is large or unlimited. |
| 579 | |
Reid Kleckner | 28f1303 | 2011-03-14 12:36:53 -0400 | [diff] [blame] | 580 | .. versionchanged:: 3.3 |
Reid Kleckner | 31aa7dd | 2011-03-14 12:02:10 -0400 | [diff] [blame] | 581 | *timeout* was added. |
| 582 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 583 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 584 | .. method:: Popen.send_signal(signal) |
| 585 | |
| 586 | Sends the signal *signal* to the child. |
| 587 | |
| 588 | .. note:: |
| 589 | |
Brian Curtin | eb24d74 | 2010-04-12 17:16:38 +0000 | [diff] [blame] | 590 | 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] | 591 | CTRL_BREAK_EVENT can be sent to processes started with a *creationflags* |
Brian Curtin | eb24d74 | 2010-04-12 17:16:38 +0000 | [diff] [blame] | 592 | parameter which includes `CREATE_NEW_PROCESS_GROUP`. |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 593 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 594 | |
| 595 | .. method:: Popen.terminate() |
| 596 | |
| 597 | Stop the child. On Posix OSs the method sends SIGTERM to the |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 598 | child. On Windows the Win32 API function :c:func:`TerminateProcess` is called |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 599 | to stop the child. |
| 600 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 601 | |
| 602 | .. method:: Popen.kill() |
| 603 | |
| 604 | Kills the child. On Posix OSs the function sends SIGKILL to the child. |
| 605 | On Windows :meth:`kill` is an alias for :meth:`terminate`. |
| 606 | |
Christian Heimes | a342c01 | 2008-04-20 21:01:16 +0000 | [diff] [blame] | 607 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 608 | The following attributes are also available: |
| 609 | |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 610 | .. warning:: |
| 611 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 612 | Use :meth:`communicate` rather than :attr:`.stdin.write <stdin>`, |
| 613 | :attr:`.stdout.read <stdout>` or :attr:`.stderr.read <stderr>` to avoid |
| 614 | deadlocks due to any of the other OS pipe buffers filling up and blocking the |
| 615 | child process. |
Georg Brandl | 734e268 | 2008-08-12 08:18:18 +0000 | [diff] [blame] | 616 | |
| 617 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 618 | .. attribute:: Popen.stdin |
| 619 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 620 | If the *stdin* argument was :data:`PIPE`, this attribute is a :term:`file |
| 621 | object` that provides input to the child process. Otherwise, it is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 622 | |
| 623 | |
| 624 | .. attribute:: Popen.stdout |
| 625 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 626 | If the *stdout* argument was :data:`PIPE`, this attribute is a :term:`file |
| 627 | object` that provides output from the child process. Otherwise, it is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 628 | |
| 629 | |
| 630 | .. attribute:: Popen.stderr |
| 631 | |
Antoine Pitrou | 11cb961 | 2010-09-15 11:11:28 +0000 | [diff] [blame] | 632 | If the *stderr* argument was :data:`PIPE`, this attribute is a :term:`file |
| 633 | object` that provides error output from the child process. Otherwise, it is |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 634 | ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 635 | |
| 636 | |
| 637 | .. attribute:: Popen.pid |
| 638 | |
| 639 | The process ID of the child process. |
| 640 | |
Georg Brandl | 58bfdca | 2010-03-21 09:50:49 +0000 | [diff] [blame] | 641 | Note that if you set the *shell* argument to ``True``, this is the process ID |
| 642 | of the spawned shell. |
| 643 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 644 | |
| 645 | .. attribute:: Popen.returncode |
| 646 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 647 | The child return code, set by :meth:`poll` and :meth:`wait` (and indirectly |
| 648 | by :meth:`communicate`). A ``None`` value indicates that the process |
| 649 | hasn't terminated yet. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 650 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 651 | A negative value ``-N`` indicates that the child was terminated by signal |
| 652 | ``N`` (Unix only). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 653 | |
| 654 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 655 | Windows Popen Helpers |
| 656 | --------------------- |
| 657 | |
| 658 | The :class:`STARTUPINFO` class and following constants are only available |
| 659 | on Windows. |
| 660 | |
| 661 | .. class:: STARTUPINFO() |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 662 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 663 | Partial support of the Windows |
| 664 | `STARTUPINFO <http://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx>`__ |
| 665 | structure is used for :class:`Popen` creation. |
| 666 | |
| 667 | .. attribute:: dwFlags |
| 668 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 669 | A bit field that determines whether certain :class:`STARTUPINFO` |
| 670 | attributes are used when the process creates a window. :: |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 671 | |
| 672 | si = subprocess.STARTUPINFO() |
| 673 | si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW |
| 674 | |
| 675 | .. attribute:: hStdInput |
| 676 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 677 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 678 | is the standard input handle for the process. If |
| 679 | :data:`STARTF_USESTDHANDLES` is not specified, the default for standard |
| 680 | input is the keyboard buffer. |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 681 | |
| 682 | .. attribute:: hStdOutput |
| 683 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 684 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 685 | is the standard output handle for the process. Otherwise, this attribute |
| 686 | 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] | 687 | buffer. |
| 688 | |
| 689 | .. attribute:: hStdError |
| 690 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 691 | If :attr:`dwFlags` specifies :data:`STARTF_USESTDHANDLES`, this attribute |
| 692 | is the standard error handle for the process. Otherwise, this attribute is |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 693 | ignored and the default for standard error is the console window's buffer. |
| 694 | |
| 695 | .. attribute:: wShowWindow |
| 696 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 697 | If :attr:`dwFlags` specifies :data:`STARTF_USESHOWWINDOW`, this attribute |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 698 | can be any of the values that can be specified in the ``nCmdShow`` |
| 699 | parameter for the |
| 700 | `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] | 701 | function, except for ``SW_SHOWDEFAULT``. Otherwise, this attribute is |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 702 | ignored. |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 703 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 704 | :data:`SW_HIDE` is provided for this attribute. It is used when |
| 705 | :class:`Popen` is called with ``shell=True``. |
| 706 | |
| 707 | |
| 708 | Constants |
| 709 | ^^^^^^^^^ |
| 710 | |
| 711 | The :mod:`subprocess` module exposes the following constants. |
| 712 | |
| 713 | .. data:: STD_INPUT_HANDLE |
| 714 | |
| 715 | The standard input device. Initially, this is the console input buffer, |
| 716 | ``CONIN$``. |
| 717 | |
| 718 | .. data:: STD_OUTPUT_HANDLE |
| 719 | |
| 720 | The standard output device. Initially, this is the active console screen |
| 721 | buffer, ``CONOUT$``. |
| 722 | |
| 723 | .. data:: STD_ERROR_HANDLE |
| 724 | |
| 725 | The standard error device. Initially, this is the active console screen |
| 726 | buffer, ``CONOUT$``. |
| 727 | |
| 728 | .. data:: SW_HIDE |
| 729 | |
| 730 | Hides the window. Another window will be activated. |
| 731 | |
| 732 | .. data:: STARTF_USESTDHANDLES |
| 733 | |
| 734 | Specifies that the :attr:`STARTUPINFO.hStdInput`, |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 735 | :attr:`STARTUPINFO.hStdOutput`, and :attr:`STARTUPINFO.hStdError` attributes |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 736 | contain additional information. |
| 737 | |
| 738 | .. data:: STARTF_USESHOWWINDOW |
| 739 | |
Senthil Kumaran | a6bac95 | 2011-07-04 11:28:30 -0700 | [diff] [blame] | 740 | Specifies that the :attr:`STARTUPINFO.wShowWindow` attribute contains |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 741 | additional information. |
| 742 | |
| 743 | .. data:: CREATE_NEW_CONSOLE |
| 744 | |
| 745 | The new process has a new console, instead of inheriting its parent's |
| 746 | console (the default). |
Brian Curtin | 73365dd | 2011-04-29 22:18:33 -0500 | [diff] [blame] | 747 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 748 | This flag is always set when :class:`Popen` is created with ``shell=True``. |
| 749 | |
Brian Curtin | 3040193 | 2011-04-29 22:20:57 -0500 | [diff] [blame] | 750 | .. data:: CREATE_NEW_PROCESS_GROUP |
| 751 | |
| 752 | A :class:`Popen` ``creationflags`` parameter to specify that a new process |
| 753 | group will be created. This flag is necessary for using :func:`os.kill` |
| 754 | on the subprocess. |
| 755 | |
| 756 | This flag is ignored if :data:`CREATE_NEW_CONSOLE` is specified. |
| 757 | |
Brian Curtin | e6242d7 | 2011-04-29 22:17:51 -0500 | [diff] [blame] | 758 | |
Benjamin Peterson | dcf97b9 | 2008-07-02 17:30:14 +0000 | [diff] [blame] | 759 | .. _subprocess-replacements: |
| 760 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 761 | Replacing Older Functions with the subprocess Module |
| 762 | ---------------------------------------------------- |
| 763 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 764 | 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] | 765 | |
| 766 | .. note:: |
| 767 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 768 | All "a" functions in this section fail (more or less) silently if the |
| 769 | executed program cannot be found; the "b" replacements raise :exc:`OSError` |
| 770 | instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 771 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 772 | In addition, the replacements using :func:`check_output` will fail with a |
| 773 | :exc:`CalledProcessError` if the requested operation produces a non-zero |
| 774 | return code. The output is still available as the ``output`` attribute of |
| 775 | the raised exception. |
| 776 | |
| 777 | In the following examples, we assume that the relevant functions have already |
| 778 | been imported from the subprocess module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 779 | |
| 780 | |
| 781 | Replacing /bin/sh shell backquote |
| 782 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 783 | |
| 784 | :: |
| 785 | |
| 786 | output=`mycmd myarg` |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 787 | # becomes |
| 788 | output = check_output(["mycmd", "myarg"]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 789 | |
| 790 | |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 791 | Replacing shell pipeline |
| 792 | ^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 793 | |
| 794 | :: |
| 795 | |
| 796 | output=`dmesg | grep hda` |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 797 | # becomes |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 798 | p1 = Popen(["dmesg"], stdout=PIPE) |
| 799 | p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE) |
Gregory P. Smith | e09d2f1 | 2011-02-05 21:47:25 +0000 | [diff] [blame] | 800 | p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 801 | output = p2.communicate()[0] |
| 802 | |
Gregory P. Smith | e09d2f1 | 2011-02-05 21:47:25 +0000 | [diff] [blame] | 803 | The p1.stdout.close() call after starting the p2 is important in order for p1 |
| 804 | to receive a SIGPIPE if p2 exits before p1. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 805 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 806 | Alternatively, for trusted input, the shell's own pipeline support may still |
| 807 | be used directly: |
| 808 | |
| 809 | output=`dmesg | grep hda` |
| 810 | # becomes |
| 811 | output=check_output("dmesg | grep hda", shell=True) |
| 812 | |
| 813 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 814 | Replacing :func:`os.system` |
| 815 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 816 | |
| 817 | :: |
| 818 | |
| 819 | sts = os.system("mycmd" + " myarg") |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 820 | # becomes |
| 821 | sts = call("mycmd" + " myarg", shell=True) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 822 | |
| 823 | Notes: |
| 824 | |
| 825 | * Calling the program through the shell is usually not required. |
| 826 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 827 | A more realistic example would look like this:: |
| 828 | |
| 829 | try: |
| 830 | retcode = call("mycmd" + " myarg", shell=True) |
| 831 | if retcode < 0: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 832 | print("Child was terminated by signal", -retcode, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 833 | else: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 834 | print("Child returned", retcode, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 835 | except OSError as e: |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 836 | print("Execution failed:", e, file=sys.stderr) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 837 | |
| 838 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 839 | Replacing the :func:`os.spawn <os.spawnl>` family |
| 840 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 841 | |
| 842 | P_NOWAIT example:: |
| 843 | |
| 844 | pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg") |
| 845 | ==> |
| 846 | pid = Popen(["/bin/mycmd", "myarg"]).pid |
| 847 | |
| 848 | P_WAIT example:: |
| 849 | |
| 850 | retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg") |
| 851 | ==> |
| 852 | retcode = call(["/bin/mycmd", "myarg"]) |
| 853 | |
| 854 | Vector example:: |
| 855 | |
| 856 | os.spawnvp(os.P_NOWAIT, path, args) |
| 857 | ==> |
| 858 | Popen([path] + args[1:]) |
| 859 | |
| 860 | Environment example:: |
| 861 | |
| 862 | os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env) |
| 863 | ==> |
| 864 | Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"}) |
| 865 | |
| 866 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 867 | |
| 868 | Replacing :func:`os.popen`, :func:`os.popen2`, :func:`os.popen3` |
| 869 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 870 | |
| 871 | :: |
| 872 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 873 | (child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 874 | ==> |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 875 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 876 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 877 | (child_stdin, child_stdout) = (p.stdin, p.stdout) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 878 | |
| 879 | :: |
| 880 | |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 881 | (child_stdin, |
| 882 | child_stdout, |
| 883 | child_stderr) = os.popen3(cmd, mode, bufsize) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 884 | ==> |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 885 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 886 | stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True) |
| 887 | (child_stdin, |
| 888 | child_stdout, |
| 889 | child_stderr) = (p.stdin, p.stdout, p.stderr) |
| 890 | |
| 891 | :: |
| 892 | |
| 893 | (child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize) |
| 894 | ==> |
| 895 | p = Popen(cmd, shell=True, bufsize=bufsize, |
| 896 | stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True) |
| 897 | (child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout) |
| 898 | |
| 899 | Return code handling translates as follows:: |
| 900 | |
| 901 | pipe = os.popen(cmd, 'w') |
| 902 | ... |
| 903 | rc = pipe.close() |
Stefan Krah | fc9e08d | 2010-07-14 10:16:11 +0000 | [diff] [blame] | 904 | if rc is not None and rc >> 8: |
Ezio Melotti | 985e24d | 2009-09-13 07:54:02 +0000 | [diff] [blame] | 905 | print("There were some errors") |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 906 | ==> |
| 907 | process = Popen(cmd, 'w', stdin=PIPE) |
| 908 | ... |
| 909 | process.stdin.close() |
| 910 | if process.wait() != 0: |
Ezio Melotti | 985e24d | 2009-09-13 07:54:02 +0000 | [diff] [blame] | 911 | print("There were some errors") |
Benjamin Peterson | 87c8d87 | 2009-06-11 22:54:11 +0000 | [diff] [blame] | 912 | |
| 913 | |
| 914 | Replacing functions from the :mod:`popen2` module |
| 915 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 916 | |
| 917 | .. note:: |
| 918 | |
| 919 | If the cmd argument to popen2 functions is a string, the command is executed |
| 920 | through /bin/sh. If it is a list, the command is directly executed. |
| 921 | |
| 922 | :: |
| 923 | |
| 924 | (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode) |
| 925 | ==> |
| 926 | p = Popen(["somestring"], shell=True, bufsize=bufsize, |
| 927 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 928 | (child_stdout, child_stdin) = (p.stdout, p.stdin) |
| 929 | |
| 930 | :: |
| 931 | |
| 932 | (child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, mode) |
| 933 | ==> |
| 934 | p = Popen(["mycmd", "myarg"], bufsize=bufsize, |
| 935 | stdin=PIPE, stdout=PIPE, close_fds=True) |
| 936 | (child_stdout, child_stdin) = (p.stdout, p.stdin) |
| 937 | |
| 938 | :class:`popen2.Popen3` and :class:`popen2.Popen4` basically work as |
| 939 | :class:`subprocess.Popen`, except that: |
| 940 | |
| 941 | * :class:`Popen` raises an exception if the execution fails. |
| 942 | |
| 943 | * the *capturestderr* argument is replaced with the *stderr* argument. |
| 944 | |
| 945 | * ``stdin=PIPE`` and ``stdout=PIPE`` must be specified. |
| 946 | |
| 947 | * 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] | 948 | ``close_fds=True`` with :class:`Popen` to guarantee this behavior on |
| 949 | all platforms or past Python versions. |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 950 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 951 | |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 952 | Legacy Shell Invocation Functions |
Nick Coghlan | 32e4a58 | 2011-11-08 21:50:58 +1000 | [diff] [blame] | 953 | --------------------------------- |
Nick Coghlan | c29248f | 2011-11-08 20:49:23 +1000 | [diff] [blame] | 954 | |
| 955 | This module also provides the following legacy functions from the 2.x |
| 956 | ``commands`` module. These operations implicitly invoke the system shell and |
| 957 | none of the guarantees described above regarding security and exception |
| 958 | handling consistency are valid for these functions. |
| 959 | |
| 960 | .. function:: getstatusoutput(cmd) |
| 961 | |
| 962 | Return ``(status, output)`` of executing *cmd* in a shell. |
| 963 | |
| 964 | Execute the string *cmd* in a shell with :func:`os.popen` and return a 2-tuple |
| 965 | ``(status, output)``. *cmd* is actually run as ``{ cmd ; } 2>&1``, so that the |
| 966 | returned output will contain output or error messages. A trailing newline is |
| 967 | stripped from the output. The exit status for the command can be interpreted |
| 968 | according to the rules for the C function :c:func:`wait`. Example:: |
| 969 | |
| 970 | >>> subprocess.getstatusoutput('ls /bin/ls') |
| 971 | (0, '/bin/ls') |
| 972 | >>> subprocess.getstatusoutput('cat /bin/junk') |
| 973 | (256, 'cat: /bin/junk: No such file or directory') |
| 974 | >>> subprocess.getstatusoutput('/bin/junk') |
| 975 | (256, 'sh: /bin/junk: not found') |
| 976 | |
| 977 | Availability: UNIX. |
| 978 | |
| 979 | |
| 980 | .. function:: getoutput(cmd) |
| 981 | |
| 982 | Return output (stdout and stderr) of executing *cmd* in a shell. |
| 983 | |
| 984 | Like :func:`getstatusoutput`, except the exit status is ignored and the return |
| 985 | value is a string containing the command's output. Example:: |
| 986 | |
| 987 | >>> subprocess.getoutput('ls /bin/ls') |
| 988 | '/bin/ls' |
| 989 | |
| 990 | Availability: UNIX. |
| 991 | |
Nick Coghlan | 32e4a58 | 2011-11-08 21:50:58 +1000 | [diff] [blame] | 992 | |
Eli Bendersky | 046a764 | 2011-04-15 07:23:26 +0300 | [diff] [blame] | 993 | Notes |
| 994 | ----- |
| 995 | |
| 996 | .. _converting-argument-sequence: |
| 997 | |
| 998 | Converting an argument sequence to a string on Windows |
| 999 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 1000 | |
| 1001 | On Windows, an *args* sequence is converted to a string that can be parsed |
| 1002 | using the following rules (which correspond to the rules used by the MS C |
| 1003 | runtime): |
| 1004 | |
| 1005 | 1. Arguments are delimited by white space, which is either a |
| 1006 | space or a tab. |
| 1007 | |
| 1008 | 2. A string surrounded by double quotation marks is |
| 1009 | interpreted as a single argument, regardless of white space |
| 1010 | contained within. A quoted string can be embedded in an |
| 1011 | argument. |
| 1012 | |
| 1013 | 3. A double quotation mark preceded by a backslash is |
| 1014 | interpreted as a literal double quotation mark. |
| 1015 | |
| 1016 | 4. Backslashes are interpreted literally, unless they |
| 1017 | immediately precede a double quotation mark. |
| 1018 | |
| 1019 | 5. If backslashes immediately precede a double quotation mark, |
| 1020 | every pair of backslashes is interpreted as a literal |
| 1021 | backslash. If the number of backslashes is odd, the last |
| 1022 | backslash escapes the next double quotation mark as |
| 1023 | described in rule 3. |
| 1024 | |
Eli Bendersky | d211231 | 2011-04-15 07:26:28 +0300 | [diff] [blame] | 1025 | |
Éric Araujo | 9bce311 | 2011-07-27 18:29:31 +0200 | [diff] [blame] | 1026 | .. seealso:: |
| 1027 | |
| 1028 | :mod:`shlex` |
| 1029 | Module which provides function to parse and escape command lines. |