Extensions peculiar to a particular operating system are also available through
the :mod:`os` module, but using them is of course a threat to portability!
+.. note::
+
+ If not separately noted, all functions that claim "Availability: Unix" are
+ supported on Mac OS X, which builds on a Unix core.
+
.. note::
All functions in this module raise :exc:`OSError` in the case of invalid or
.. data:: path
The corresponding operating system dependent standard module for pathname
- operations, such as :mod:`posixpath` or :mod:`macpath`. Thus, given the proper
+ operations, such as :mod:`posixpath` or :mod:`ntpath`. Thus, given the proper
imports, ``os.path.split(file)`` is equivalent to but more portable than
``posixpath.split(file)``. Note that this is also an importable module: it may
be imported directly as :mod:`os.path`.
.. note::
- On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may cause
- memory leaks. Refer to the system documentation for :cfunc:`putenv`.
+ On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
+ cause memory leaks. Refer to the system documentation for
+ :cfunc:`putenv`.
If :func:`putenv` is not provided, a modified copy of this mapping may be
passed to the appropriate process-creation functions to cause child processes
.. note::
- On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may cause
- memory leaks. Refer to the system documentation for putenv.
+ On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
+ cause memory leaks. Refer to the system documentation for putenv.
When :func:`putenv` is supported, assignments to items in ``os.environ`` are
automatically translated into corresponding calls to :func:`putenv`; however,
Return an open file object connected to the file descriptor *fd*. The *mode*
and *bufsize* arguments have the same meaning as the corresponding arguments to
- the built-in :func:`open` function. Availability: Macintosh, Unix, Windows.
+ the built-in :func:`open` function. Availability: Unix, Windows.
When specified, the *mode* argument must start with one of the letters
``'r'``, ``'w'``, or ``'a'``, otherwise a :exc:`ValueError` is raised.
.. function:: close(fd)
- Close file descriptor *fd*. Availability: Macintosh, Unix, Windows.
+ Close file descriptor *fd*. Availability: Unix, Windows.
.. note::
.. function:: closerange(fd_low, fd_high)
Close all file descriptors from *fd_low* (inclusive) to *fd_high* (exclusive),
- ignoring errors. Availability: Macintosh, Unix, Windows. Equivalent to::
+ ignoring errors. Availability: Unix, Windows. Equivalent to::
for fd in xrange(fd_low, fd_high):
try:
.. function:: dup(fd)
- Return a duplicate of file descriptor *fd*. Availability: Macintosh, Unix,
+ Return a duplicate of file descriptor *fd*. Availability: Unix,
Windows.
.. function:: dup2(fd, fd2)
Duplicate file descriptor *fd* to *fd2*, closing the latter first if necessary.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. function:: fchmod(fd, mode)
additional names as well. The names known to the host operating system are
given in the ``pathconf_names`` dictionary. For configuration variables not
included in that mapping, passing an integer for *name* is also accepted.
- Availability: Macintosh, Unix.
+ Availability: Unix.
If *name* is a string and is not known, :exc:`ValueError` is raised. If a
specific value for *name* is not supported by the host system, even if it is
.. function:: fstat(fd)
Return status for file descriptor *fd*, like :func:`stat`. Availability:
- Macintosh, Unix, Windows.
+ Unix, Windows.
.. function:: fstatvfs(fd)
If you're starting with a Python file object *f*, first do ``f.flush()``, and
then do ``os.fsync(f.fileno())``, to ensure that all internal buffers associated
- with *f* are written to disk. Availability: Macintosh, Unix, and Windows.
+ with *f* are written to disk. Availability: Unix, Windows.
.. function:: ftruncate(fd, length)
Truncate the file corresponding to file descriptor *fd*, so that it is at most
- *length* bytes in size. Availability: Macintosh, Unix.
+ *length* bytes in size. Availability: Unix.
.. function:: isatty(fd)
Return ``True`` if the file descriptor *fd* is open and connected to a
- tty(-like) device, else ``False``. Availability: Macintosh, Unix.
+ tty(-like) device, else ``False``. Availability: Unix.
.. function:: lseek(fd, pos, how)
by *how*: :const:`SEEK_SET` or ``0`` to set the position relative to the
beginning of the file; :const:`SEEK_CUR` or ``1`` to set it relative to the
current position; :const:`os.SEEK_END` or ``2`` to set it relative to the end of
- the file. Availability: Macintosh, Unix, Windows.
+ the file. Availability: Unix, Windows.
.. function:: open(file, flags[, mode])
Open the file *file* and set various flags according to *flags* and possibly
its mode according to *mode*. The default *mode* is ``0o777`` (octal), and
the current umask value is first masked out. Return the file descriptor for
- the newly opened file. Availability: Macintosh, Unix, Windows.
+ the newly opened file. Availability: Unix, Windows.
For a description of the flag and mode values, see the C run-time documentation;
flag constants (like :const:`O_RDONLY` and :const:`O_WRONLY`) are defined in
Open a new pseudo-terminal pair. Return a pair of file descriptors ``(master,
slave)`` for the pty and the tty, respectively. For a (slightly) more portable
- approach, use the :mod:`pty` module. Availability: Macintosh, some flavors of
+ approach, use the :mod:`pty` module. Availability: some flavors of
Unix.
.. function:: pipe()
Create a pipe. Return a pair of file descriptors ``(r, w)`` usable for reading
- and writing, respectively. Availability: Macintosh, Unix, Windows.
+ and writing, respectively. Availability: Unix, Windows.
.. function:: read(fd, n)
Read at most *n* bytes from file descriptor *fd*. Return a string containing the
bytes read. If the end of the file referred to by *fd* has been reached, an
- empty string is returned. Availability: Macintosh, Unix, Windows.
+ empty string is returned. Availability: Unix, Windows.
.. note::
.. function:: tcgetpgrp(fd)
Return the process group associated with the terminal given by *fd* (an open
- file descriptor as returned by :func:`open`). Availability: Macintosh, Unix.
+ file descriptor as returned by :func:`open`). Availability: Unix.
.. function:: tcsetpgrp(fd, pg)
Set the process group associated with the terminal given by *fd* (an open file
- descriptor as returned by :func:`open`) to *pg*. Availability: Macintosh, Unix.
+ descriptor as returned by :func:`open`) to *pg*. Availability: Unix.
.. function:: ttyname(fd)
Return a string which specifies the terminal device associated with
file descriptor *fd*. If *fd* is not associated with a terminal device, an
- exception is raised. Availability:Macintosh, Unix.
+ exception is raised. Availability: Unix.
.. function:: write(fd, str)
Write the string *str* to file descriptor *fd*. Return the number of bytes
- actually written. Availability: Macintosh, Unix, Windows.
+ actually written. Availability: Unix, Windows.
.. note::
O_TRUNC
Options for the *flag* argument to the :func:`open` function. These can be
- combined using the bitwise OR operator ``|``. Availability: Macintosh, Unix, Windows.
+ combined using the bitwise OR operator ``|``. Availability: Unix, Windows.
.. data:: O_DSYNC
O_EXLOCK
More options for the *flag* argument to the :func:`open` function. Availability:
- Macintosh, Unix.
+ Unix.
.. data:: O_BINARY
SEEK_END
Parameters to the :func:`lseek` function. Their values are 0, 1, and 2,
- respectively. Availability: Windows, Macintosh, Unix.
+ respectively. Availability: Windows, Unix.
.. _os-file-dir:
can be the inclusive OR of one or more of :const:`R_OK`, :const:`W_OK`, and
:const:`X_OK` to test permissions. Return :const:`True` if access is allowed,
:const:`False` if not. See the Unix man page :manpage:`access(2)` for more
- information. Availability: Macintosh, Unix, Windows.
+ information. Availability: Unix, Windows.
.. note::
.. index:: single: directory; changing
- Change the current working directory to *path*. Availability: Macintosh, Unix,
+ Change the current working directory to *path*. Availability: Unix,
Windows.
.. function:: getcwd()
Return a bytestring representing the current working directory.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. function:: getcwdu()
Return a string representing the current working directory.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. function:: chflags(path, flags)
* ``SF_NOUNLINK``
* ``SF_SNAPSHOT``
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. function:: chroot(path)
Change the root directory of the current process to *path*. Availability:
- Macintosh, Unix.
+ Unix.
.. function:: chmod(path, mode)
* ``stat.S_IWOTH``
* ``stat.S_IXOTH``
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. note::
.. function:: chown(path, uid, gid)
Change the owner and group id of *path* to the numeric *uid* and *gid*. To leave
- one of the ids unchanged, set it to -1. Availability: Macintosh, Unix.
+ one of the ids unchanged, set it to -1. Availability: Unix.
.. function:: lchflags(path, flags)
.. function:: lchown(path, uid, gid)
Change the owner and group id of *path* to the numeric *uid* and *gid*. This
- function will not follow symbolic links. Availability: Macintosh, Unix.
+ function will not follow symbolic links. Availability: Unix.
.. function:: link(src, dst)
- Create a hard link pointing to *src* named *dst*. Availability: Macintosh, Unix.
+ Create a hard link pointing to *src* named *dst*. Availability: Unix.
.. function:: listdir(path)
Return a list containing the names of the entries in the directory. The list is
in arbitrary order. It does not include the special entries ``'.'`` and
- ``'..'`` even if they are present in the directory. Availability: Macintosh,
+ ``'..'`` even if they are present in the directory. Availability:
Unix, Windows.
On Windows NT/2k/XP and Unix, if *path* is a Unicode object, the result will be
Create a FIFO (a named pipe) named *path* with numeric mode *mode*. The
default *mode* is ``0o666`` (octal). The current umask value is first masked
- out from the mode. Availability: Macintosh, Unix.
+ out from the mode. Availability: Unix.
FIFOs are pipes that can be accessed like regular files. FIFOs exist until they
are deleted (for example with :func:`os.unlink`). Generally, FIFOs are used as
Create a directory named *path* with numeric mode *mode*. The default *mode*
is ``0o777`` (octal). On some systems, *mode* is ignored. Where it is used,
- the current umask value is first masked out. Availability: Macintosh, Unix,
- Windows.
+ the current umask value is first masked out. Availability: Unix, Windows.
It is also possible to create temporary directories; see the
:mod:`tempfile` module's :func:`tempfile.mkdtemp` function.
additional names as well. The names known to the host operating system are
given in the ``pathconf_names`` dictionary. For configuration variables not
included in that mapping, passing an integer for *name* is also accepted.
- Availability: Macintosh, Unix.
+ Availability: Unix.
If *name* is a string and is not known, :exc:`ValueError` is raised. If a
specific value for *name* is not supported by the host system, even if it is
Dictionary mapping names accepted by :func:`pathconf` and :func:`fpathconf` to
the integer values defined for those names by the host operating system. This
can be used to determine the set of names known to the system. Availability:
- Macintosh, Unix.
+ Unix.
.. function:: readlink(path)
If the *path* is a Unicode object, the result will also be a Unicode object.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. function:: remove(path)
:func:`unlink` function documented below. On Windows, attempting to remove a
file that is in use causes an exception to be raised; on Unix, the directory
entry is removed but the storage allocated to the file is not made available
- until the original file is no longer in use. Availability: Macintosh, Unix,
+ until the original file is no longer in use. Availability: Unix,
Windows.
the renaming will be an atomic operation (this is a POSIX requirement). On
Windows, if *dst* already exists, :exc:`OSError` will be raised even if it is a
file; there may be no way to implement an atomic rename when *dst* names an
- existing file. Availability: Macintosh, Unix, Windows.
+ existing file. Availability: Unix, Windows.
.. function:: renames(old, new)
.. function:: rmdir(path)
- Remove the directory *path*. Availability: Macintosh, Unix, Windows.
+ Remove the directory *path*. Availability: Unix, Windows.
.. function:: stat(path)
:attr:`st_mtime` has 2-second resolution, and :attr:`st_atime` has only 1-day
resolution. See your operating system documentation for details.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. function:: stat_float_times([newvalue])
.. function:: unlink(path)
Remove the file *path*. This is the same function as :func:`remove`; the
- :func:`unlink` name is its traditional Unix name. Availability: Macintosh, Unix,
+ :func:`unlink` name is its traditional Unix name. Availability: Unix,
Windows.
subsequent :func:`stat` call, depending on the resolution with which your
operating system records access and modification times; see :func:`stat`.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. function:: walk(top[, topdown=True [, onerror=None[, followlinks=False]]])
behavior is to produce a core dump; on Windows, the process immediately returns
an exit code of ``3``. Be aware that programs which use :func:`signal.signal`
to register a handler for :const:`SIGABRT` will behave differently.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
.. function:: execl(path, arg0, arg1, ...)
used to define the environment variables for the new process (these are used
instead of the current process' environment); the functions :func:`execl`,
:func:`execlp`, :func:`execv`, and :func:`execvp` all cause the new process to
- inherit the environment of the current process. Availability: Macintosh, Unix,
+ inherit the environment of the current process. Availability: Unix,
Windows.
.. function:: _exit(n)
Exit to the system with status *n*, without calling cleanup handlers, flushing
- stdio buffers, etc. Availability: Macintosh, Unix, Windows.
+ stdio buffers, etc. Availability: Unix, Windows.
.. note::
.. data:: EX_OK
- Exit code that means no error occurred. Availability: Macintosh, Unix.
+ Exit code that means no error occurred. Availability: Unix.
.. data:: EX_USAGE
Exit code that means the command was used incorrectly, such as when the wrong
- number of arguments are given. Availability: Macintosh, Unix.
+ number of arguments are given. Availability: Unix.
.. data:: EX_DATAERR
- Exit code that means the input data was incorrect. Availability: Macintosh,
- Unix.
+ Exit code that means the input data was incorrect. Availability: Unix.
.. data:: EX_NOINPUT
Exit code that means an input file did not exist or was not readable.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. data:: EX_NOUSER
- Exit code that means a specified user did not exist. Availability: Macintosh,
- Unix.
+ Exit code that means a specified user did not exist. Availability: Unix.
.. data:: EX_NOHOST
- Exit code that means a specified host did not exist. Availability: Macintosh,
- Unix.
+ Exit code that means a specified host did not exist. Availability: Unix.
.. data:: EX_UNAVAILABLE
Exit code that means that a required service is unavailable. Availability:
- Macintosh, Unix.
+ Unix.
.. data:: EX_SOFTWARE
Exit code that means an internal software error was detected. Availability:
- Macintosh, Unix.
+ Unix.
.. data:: EX_OSERR
Exit code that means an operating system error was detected, such as the
- inability to fork or create a pipe. Availability: Macintosh, Unix.
+ inability to fork or create a pipe. Availability: Unix.
.. data:: EX_OSFILE
Exit code that means some system file did not exist, could not be opened, or had
- some other kind of error. Availability: Macintosh, Unix.
+ some other kind of error. Availability: Unix.
.. data:: EX_CANTCREAT
Exit code that means a user specified output file could not be created.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. data:: EX_IOERR
Exit code that means that an error occurred while doing I/O on some file.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. data:: EX_TEMPFAIL
Exit code that means a temporary failure occurred. This indicates something
that may not really be an error, such as a network connection that couldn't be
- made during a retryable operation. Availability: Macintosh, Unix.
+ made during a retryable operation. Availability: Unix.
.. data:: EX_PROTOCOL
Exit code that means that a protocol exchange was illegal, invalid, or not
- understood. Availability: Macintosh, Unix.
+ understood. Availability: Unix.
.. data:: EX_NOPERM
Exit code that means that there were insufficient permissions to perform the
- operation (but not intended for file system problems). Availability: Macintosh,
- Unix.
+ operation (but not intended for file system problems). Availability: Unix.
.. data:: EX_CONFIG
Exit code that means that some kind of configuration error occurred.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. data:: EX_NOTFOUND
Exit code that means something like "an entry was not found". Availability:
- Macintosh, Unix.
+ Unix.
.. function:: fork()
Fork a child process. Return ``0`` in the child and the child's process id in the
parent. If an error occurs :exc:`OSError` is raised.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. function:: forkpty()
new child's process id in the parent, and *fd* is the file descriptor of the
master end of the pseudo-terminal. For a more portable approach, use the
:mod:`pty` module. If an error occurs :exc:`OSError` is raised.
- Availability: Macintosh, some flavors of Unix.
+ Availability: some flavors of Unix.
.. function:: kill(pid, sig)
Send signal *sig* to the process *pid*. Constants for the specific signals
available on the host platform are defined in the :mod:`signal` module.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. function:: killpg(pgid, sig)
single: process; killing
single: process; signalling
- Send the signal *sig* to the process group *pgid*. Availability: Macintosh,
- Unix.
+ Send the signal *sig* to the process group *pgid*. Availability: Unix.
.. function:: nice(increment)
Add *increment* to the process's "niceness". Return the new niceness.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. function:: plock(op)
Lock program segments into memory. The value of *op* (defined in
- ``<sys/lock.h>``) determines which segments are locked. Availability: Macintosh,
- Unix.
+ ``<sys/lock.h>``) determines which segments are locked. Availability: Unix.
.. function:: popen(...)
Possible values for the *mode* parameter to the :func:`spawn\*` family of
functions. If either of these values is given, the :func:`spawn\*` functions
will return as soon as the new process has been created, with the process id as
- the return value. Availability: Macintosh, Unix, Windows.
+ the return value. Availability: Unix, Windows.
.. data:: P_WAIT
functions. If this is given as *mode*, the :func:`spawn\*` functions will not
return until the new process has run to completion and will return the exit code
of the process the run is successful, or ``-signal`` if a signal kills the
- process. Availability: Macintosh, Unix, Windows.
+ process. Availability: Unix, Windows.
.. data:: P_DETACH
the command run; on systems using a non-native shell, consult your shell
documentation.
- Availability: Macintosh, Unix, Windows.
+ Availability: Unix, Windows.
The :mod:`subprocess` module provides more powerful facilities for spawning new
processes and retrieving their results; using that module is preferable to using
other) times, in seconds. The items are: user time, system time, children's
user time, children's system time, and elapsed real time since a fixed point in
the past, in that order. See the Unix manual page :manpage:`times(2)` or the
- corresponding Windows Platform API documentation. Availability: Macintosh, Unix,
+ corresponding Windows Platform API documentation. Availability: Unix,
Windows. On Windows, only the first two items are filled, the others are zero.
and exit status indication: a 16-bit number, whose low byte is the signal number
that killed the process, and whose high byte is the exit status (if the signal
number is zero); the high bit of the low byte is set if a core file was
- produced. Availability: Macintosh, Unix.
+ produced. Availability: Unix.
.. function:: waitpid(pid, options)
The option for :func:`waitpid` to return immediately if no child process status
is available immediately. The function returns ``(0, 0)`` in this case.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. data:: WCONTINUED
This option causes child processes to be reported if they have been stopped but
their current state has not been reported since they were stopped. Availability:
- Macintosh, Unix.
+ Unix.
The following functions take a process status code as returned by
.. function:: WCOREDUMP(status)
Return ``True`` if a core dump was generated for the process, otherwise
- return ``False``. Availability: Macintosh, Unix.
+ return ``False``. Availability: Unix.
.. function:: WIFCONTINUED(status)
.. function:: WIFSIGNALED(status)
Return ``True`` if the process exited due to a signal, otherwise return
- ``False``. Availability: Macintosh, Unix.
+ ``False``. Availability: Unix.
.. function:: WIFEXITED(status)
Return ``True`` if the process exited using the :manpage:`exit(2)` system call,
- otherwise return ``False``. Availability: Macintosh, Unix.
+ otherwise return ``False``. Availability: Unix.
.. function:: WEXITSTATUS(status)
If ``WIFEXITED(status)`` is true, return the integer parameter to the
:manpage:`exit(2)` system call. Otherwise, the return value is meaningless.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. function:: WSTOPSIG(status)
- Return the signal which caused the process to stop. Availability: Macintosh,
- Unix.
+ Return the signal which caused the process to stop. Availability: Unix.
.. function:: WTERMSIG(status)
- Return the signal which caused the process to exit. Availability: Macintosh,
- Unix.
+ Return the signal which caused the process to exit. Availability: Unix.
.. _os-path:
The names known to the host operating system are given as the keys of the
``confstr_names`` dictionary. For configuration variables not included in that
mapping, passing an integer for *name* is also accepted. Availability:
- Macintosh, Unix.
+ Unix.
If the configuration value specified by *name* isn't defined, ``None`` is
returned.
Dictionary mapping names accepted by :func:`confstr` to the integer values
defined for those names by the host operating system. This can be used to
- determine the set of names known to the system. Availability: Macintosh, Unix.
+ determine the set of names known to the system. Availability: Unix.
.. function:: getloadavg()
specified by *name* isn't defined, ``-1`` is returned. The comments regarding
the *name* parameter for :func:`confstr` apply here as well; the dictionary that
provides information on the known names is given by ``sysconf_names``.
- Availability: Macintosh, Unix.
+ Availability: Unix.
.. data:: sysconf_names
Dictionary mapping names accepted by :func:`sysconf` to the integer values
defined for those names by the host operating system. This can be used to
- determine the set of names known to the system. Availability: Macintosh, Unix.
+ determine the set of names known to the system. Availability: Unix.
The following data values are used to support path manipulation operations. These
are defined for all platforms.
.. data:: curdir
The constant string used by the operating system to refer to the current
- directory. For example: ``'.'`` for POSIX or ``':'`` for Mac OS 9. Also
- available via :mod:`os.path`.
+ directory. This is ``'.'`` for Windows and POSIX. Also available via
+ :mod:`os.path`.
.. data:: pardir
The constant string used by the operating system to refer to the parent
- directory. For example: ``'..'`` for POSIX or ``'::'`` for Mac OS 9. Also
- available via :mod:`os.path`.
+ directory. This is ``'..'`` for Windows and POSIX. Also available via
+ :mod:`os.path`.
.. data:: sep
- The character used by the operating system to separate pathname components, for
- example, ``'/'`` for POSIX or ``':'`` for Mac OS 9. Note that knowing this is
- not sufficient to be able to parse or concatenate pathnames --- use
+ The character used by the operating system to separate pathname components.
+ This is ``'/'`` for POSIX and ``'\\'`` for Windows. Note that knowing this
+ is not sufficient to be able to parse or concatenate pathnames --- use
:func:`os.path.split` and :func:`os.path.join` --- but it is occasionally
useful. Also available via :mod:`os.path`.
.. data:: linesep
The string used to separate (or, rather, terminate) lines on the current
- platform. This may be a single character, such as ``'\n'`` for POSIX or
- ``'\r'`` for Mac OS, or multiple characters, for example, ``'\r\n'`` for
- Windows. Do not use *os.linesep* as a line terminator when writing files opened
- in text mode (the default); use a single ``'\n'`` instead, on all platforms.
+ platform. This may be a single character, such as ``'\n'`` for POSIX, or
+ multiple characters, for example, ``'\r\n'`` for Windows. Do not use
+ *os.linesep* as a line terminator when writing files opened in text mode (the
+ default); use a single ``'\n'`` instead, on all platforms.
.. data:: devnull
- The file path of the null device. For example: ``'/dev/null'`` for POSIX or
- ``'Dev:Nul'`` for Mac OS 9. Also available via :mod:`os.path`.
+ The file path of the null device. For example: ``'/dev/null'`` for POSIX.
+ Also available via :mod:`os.path`.
.. _os-miscfunc:
projects / python / commitdiff