507 lines
17 KiB
TeX
507 lines
17 KiB
TeX
\section{Built-in Module \sectcode{posix}}
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\label{module-posix}
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\bimodindex{posix}
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This module provides access to operating system functionality that is
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standardized by the C Standard and the \POSIX{} standard (a thinly disguised
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\UNIX{} interface).
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\strong{Do not import this module directly.} Instead, import the
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module \code{os}, which provides a \emph{portable} version of this
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interface. On \UNIX{}, the \code{os} module provides a superset of
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the \code{posix} interface. On non-\UNIX{} operating systems the
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\code{posix} module is not available, but a subset is always available
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through the \code{os} interface. Once \code{os} is imported, there is
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\emph{no} performance penalty in using it instead of
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\code{posix}. In addition, \code{os} provides some additional
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functionality, such as automatically calling \code{putenv()}
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when an entry is \code{os.environ} is changed.
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\refstmodindex{os}
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The descriptions below are very terse; refer to the corresponding
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\UNIX{} manual (or \POSIX{} documentation) entry for more information.
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Arguments called \var{path} refer to a pathname given as a string.
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Errors are reported as exceptions; the usual exceptions are given
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for type errors, while errors reported by the system calls raise
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\code{posix.error}, described below.
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Module \code{posix} defines the following data items:
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\setindexsubitem{(data in module posix)}
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\begin{datadesc}{environ}
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A dictionary representing the string environment at the time
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the interpreter was started.
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For example,
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\code{posix.environ['HOME']}
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is the pathname of your home directory, equivalent to
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\code{getenv("HOME")}
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in C.
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Modifying this dictionary does not affect the string environment
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passed on by \code{execv()}, \code{popen()} or \code{system()}; if you
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need to change the environment, pass \code{environ} to \code{execve()}
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or add variable assignments and export statements to the command
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string for \code{system()} or \code{popen()}.
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\emph{However:} If you are using this module via the \code{os} module
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(as you should -- see the introduction above), \code{environ} is a
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a mapping object that behaves almost like a dictionary but invokes
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\code{putenv()} automatically called whenever an item is changed.
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\end{datadesc}
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\setindexsubitem{(exception in module posix)}
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\begin{excdesc}{error}
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This exception is raised when a \POSIX{} function returns a
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\POSIX{}-related error (e.g., not for illegal argument types). Its
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string value is \code{'posix.error'}. The accompanying value is a
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pair containing the numeric error code from \code{errno} and the
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corresponding string, as would be printed by the C function
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\code{perror()}.
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See the module \module{errno}\refbimodindex{errno}, which contains
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names for the error codes defined by the underlying operating system.
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\end{excdesc}
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It defines the following functions and constants:
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\setindexsubitem{(in module posix)}
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\begin{funcdesc}{chdir}{path}
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Change the current working directory to \var{path}.
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\end{funcdesc}
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\begin{funcdesc}{chmod}{path\, mode}
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Change the mode of \var{path} to the numeric \var{mode}.
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\end{funcdesc}
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\begin{funcdesc}{chown}{path\, uid, gid}
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Change the owner and group id of \var{path} to the numeric \var{uid}
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and \var{gid}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{close}{fd}
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Close file descriptor \var{fd}.
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Note: this function is intended for low-level I/O and must be applied
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to a file descriptor as returned by \code{posix.open()} or
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\code{posix.pipe()}. To close a ``file object'' returned by the
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built-in function \code{open} or by \code{posix.popen} or
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\code{posix.fdopen}, use its \code{close()} method.
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\end{funcdesc}
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\begin{funcdesc}{dup}{fd}
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Return a duplicate of file descriptor \var{fd}.
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\end{funcdesc}
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\begin{funcdesc}{dup2}{fd\, fd2}
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Duplicate file descriptor \var{fd} to \var{fd2}, closing the latter
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first if necessary. Return \code{None}.
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\end{funcdesc}
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\begin{funcdesc}{execv}{path\, args}
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Execute the executable \var{path} with argument list \var{args},
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replacing the current process (i.e., the Python interpreter).
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The argument list may be a tuple or list of strings.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{execve}{path\, args\, env}
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Execute the executable \var{path} with argument list \var{args},
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and environment \var{env},
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replacing the current process (i.e., the Python interpreter).
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The argument list may be a tuple or list of strings.
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The environment must be a dictionary mapping strings to strings.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{_exit}{n}
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Exit to the system with status \var{n}, without calling cleanup
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handlers, flushing stdio buffers, etc.
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(Not on MS-DOS.)
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Note: the standard way to exit is \code{sys.exit(\var{n})}.
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\code{posix._exit()} should normally only be used in the child process
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after a \code{fork()}.
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\end{funcdesc}
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\begin{funcdesc}{fdopen}{fd\optional{\, mode\optional{\, bufsize}}}
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Return an open file object connected to the file descriptor \var{fd}.
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The \var{mode} and \var{bufsize} arguments have the same meaning as
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the corresponding arguments to the built-in \code{open()} function.
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\end{funcdesc}
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\begin{funcdesc}{fork}{}
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Fork a child process. Return 0 in the child, the child's process id
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in the parent.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{fstat}{fd}
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Return status for file descriptor \var{fd}, like \code{stat()}.
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\end{funcdesc}
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\begin{funcdesc}{ftruncate}{fd\, length}
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Truncate the file corresponding to file descriptor \var{fd},
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so that it is at most \var{length} bytes in size.
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\end{funcdesc}
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\begin{funcdesc}{getcwd}{}
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Return a string representing the current working directory.
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\end{funcdesc}
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\begin{funcdesc}{getegid}{}
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Return the current process' effective group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{geteuid}{}
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Return the current process' effective user id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getgid}{}
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Return the current process' group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getpgrp}{}
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Return the current process group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getpid}{}
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Return the current process id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getppid}{}
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Return the parent's process id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{getuid}{}
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Return the current process' user id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{kill}{pid\, sig}
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Kill the process \var{pid} with signal \var{sig}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{link}{src\, dst}
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Create a hard link pointing to \var{src} named \var{dst}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{listdir}{path}
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Return a list containing the names of the entries in the directory.
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The list is in arbitrary order. It does not include the special
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entries \code{'.'} and \code{'..'} even if they are present in the
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directory.
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\end{funcdesc}
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\begin{funcdesc}{lseek}{fd\, pos\, how}
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Set the current position of file descriptor \var{fd} to position
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\var{pos}, modified by \var{how}: 0 to set the position relative to
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the beginning of the file; 1 to set it relative to the current
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position; 2 to set it relative to the end of the file.
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\end{funcdesc}
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\begin{funcdesc}{lstat}{path}
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Like \code{stat()}, but do not follow symbolic links. (On systems
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without symbolic links, this is identical to \code{posix.stat()}.)
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\end{funcdesc}
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\begin{funcdesc}{mkfifo}{path\optional{\, mode}}
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Create a FIFO (a \POSIX{} named pipe) named \var{path} with numeric mode
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\var{mode}. The default \var{mode} is 0666 (octal). The current
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umask value is first masked out from the mode.
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(Not on MS-DOS.)
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FIFOs are pipes that can be accessed like regular files. FIFOs exist
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until they are deleted (for example with \code{os.unlink}).
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Generally, FIFOs are used as rendez-vous between ``client'' and
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``server'' type processes: the server opens the FIFO for reading, and
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the client opens it for writing. Note that \code{mkfifo()} doesn't
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open the FIFO -- it just creates the rendez-vous point.
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\end{funcdesc}
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\begin{funcdesc}{mkdir}{path\optional{\, mode}}
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Create a directory named \var{path} with numeric mode \var{mode}.
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The default \var{mode} is 0777 (octal). On some systems, \var{mode}
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is ignored. Where it is used, the current umask value is first
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masked out.
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\end{funcdesc}
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\begin{funcdesc}{nice}{increment}
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Add \var{incr} to the process' ``niceness''. Return the new niceness.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{open}{file\, flags\optional{\, mode}}
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Open the file \var{file} and set various flags according to
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\var{flags} and possibly its mode according to \var{mode}.
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The default \var{mode} is 0777 (octal), and the current umask value is
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first masked out. Return the file descriptor for the newly opened
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file.
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For a description of the flag and mode values, see the \UNIX{} or C
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run-time documentation; flag constants (like \code{O_RDONLY} and
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\code{O_WRONLY}) are defined in this module too (see below).
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Note: this function is intended for low-level I/O. For normal usage,
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use the built-in function \code{open}, which returns a ``file object''
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with \code{read()} and \code{write()} methods (and many more).
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\end{funcdesc}
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\begin{funcdesc}{pipe}{}
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Create a pipe. Return a pair of file descriptors \code{(r, w)}
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usable for reading and writing, respectively.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{plock}{op}
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Lock program segments into memory. The value of \var{op}
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(defined in \code{<sys/lock.h>}) determines which segments are locked.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{popen}{command\optional{\, mode\optional{\, bufsize}}}
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Open a pipe to or from \var{command}. The return value is an open
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file object connected to the pipe, which can be read or written
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depending on whether \var{mode} is \code{'r'} (default) or \code{'w'}.
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The \var{bufsize} argument has the same meaning as the corresponding
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argument to the built-in \code{open()} function. The exit status of
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the command (encoded in the format specified for \code{wait()}) is
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available as the return value of the \code{close()} method of the file
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object.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{putenv}{varname\, value}
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Set the environment variable named \var{varname} to the string \var{value}.
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Such changes to the environment affect
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subprocesses started with \code{os.system()}, \code{os.popen()} or
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\code{os.fork()} and \code{os.execv()}. (Not on all systems.)
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When \code{putenv()} is
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supported, assignments to items in \code{os.environ} are automatically
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translated into corresponding calls to \code{os.putenv()}; however,
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calls to \code{os.putenv()} don't update \code{os.environ}, so it is
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actually preferable to assign to items of \code{os.environ}.
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\end{funcdesc}
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\begin{funcdesc}{strerror}{code}
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Return the error message corresponding to the error code in \var{code}.
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\end{funcdesc}
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\begin{funcdesc}{read}{fd\, n}
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Read at most \var{n} bytes from file descriptor \var{fd}.
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Return a string containing the bytes read.
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Note: this function is intended for low-level I/O and must be applied
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to a file descriptor as returned by \code{posix.open()} or
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\code{posix.pipe()}. To read a ``file object'' returned by the
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built-in function \code{open} or by \code{posix.popen} or
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\code{posix.fdopen}, or \code{sys.stdin}, use its
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\code{read()} or \code{readline()} methods.
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\end{funcdesc}
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\begin{funcdesc}{readlink}{path}
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Return a string representing the path to which the symbolic link
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points. (On systems without symbolic links, this always raises
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\code{posix.error}.)
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\end{funcdesc}
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\begin{funcdesc}{remove}{path}
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Remove the file \var{path}. See \code{rmdir} below to remove a directory.
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This is identical to the \code{unlink} function documented below.
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\end{funcdesc}
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\begin{funcdesc}{rename}{src\, dst}
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Rename the file or directory \var{src} to \var{dst}.
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\end{funcdesc}
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\begin{funcdesc}{rmdir}{path}
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Remove the directory \var{path}.
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\end{funcdesc}
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\begin{funcdesc}{setgid}{gid}
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Set the current process' group id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setpgrp}{}
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Calls the system call \code{setpgrp()} or \code{setpgrp(0, 0)}
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depending on which version is implemented (if any). See the \UNIX{}
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manual for the semantics.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setpgid}{pid\, pgrp}
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Calls the system call \code{setpgid()}. See the \UNIX{} manual for
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the semantics.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setsid}{}
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Calls the system call \code{setsid()}. See the \UNIX{} manual for the
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semantics.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{setuid}{uid}
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Set the current process' user id.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{stat}{path}
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Perform a \emph{stat} system call on the given path. The return value
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is a tuple of at least 10 integers giving the most important (and
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portable) members of the \emph{stat} structure, in the order
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\code{st_mode},
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\code{st_ino},
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\code{st_dev},
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\code{st_nlink},
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\code{st_uid},
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\code{st_gid},
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\code{st_size},
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\code{st_atime},
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\code{st_mtime},
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\code{st_ctime}.
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More items may be added at the end by some implementations.
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(On MS-DOS, some items are filled with dummy values.)
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Note: The standard module \code{stat} defines functions and constants
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that are useful for extracting information from a stat structure.
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\refstmodindex{stat}
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\end{funcdesc}
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\begin{funcdesc}{symlink}{src\, dst}
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Create a symbolic link pointing to \var{src} named \var{dst}. (On
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systems without symbolic links, this always raises
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\code{posix.error}.)
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\end{funcdesc}
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\begin{funcdesc}{system}{command}
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Execute the command (a string) in a subshell. This is implemented by
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calling the Standard C function \code{system()}, and has the same
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limitations. Changes to \code{posix.environ}, \code{sys.stdin} etc.\ are
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not reflected in the environment of the executed command. The return
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value is the exit status of the process encoded in the format
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specified for \code{wait()}.
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\end{funcdesc}
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\begin{funcdesc}{tcgetpgrp}{fd}
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Return the process group associated with the terminal given by
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\var{fd} (an open file descriptor as returned by \code{posix.open()}).
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{tcsetpgrp}{fd\, pg}
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Set the process group associated with the terminal given by
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\var{fd} (an open file descriptor as returned by \code{posix.open()})
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to \var{pg}.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{times}{}
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Return a 5-tuple of floating point numbers indicating accumulated (CPU
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or other)
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times, in seconds. The items are: user time, system time, children's
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user time, children's system time, and elapsed real time since a fixed
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point in the past, in that order. See the \UNIX{}
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manual page \emph{times}(2). (Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{umask}{mask}
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Set the current numeric umask and returns the previous umask.
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(Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{uname}{}
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Return a 5-tuple containing information identifying the current
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operating system. The tuple contains 5 strings:
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\code{(\var{sysname}, \var{nodename}, \var{release}, \var{version}, \var{machine})}.
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Some systems truncate the nodename to 8
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characters or to the leading component; a better way to get the
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hostname is \code{socket.gethostname()} or even
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\code{socket.gethostbyaddr(socket.gethostname())}.
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(Not on MS-DOS, nor on older \UNIX{} systems.)
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\end{funcdesc}
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\begin{funcdesc}{unlink}{path}
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Remove the file \var{path}. This is the same function as \code{remove};
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the \code{unlink} name is its traditional \UNIX{} name.
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\end{funcdesc}
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\begin{funcdesc}{utime}{path\, {\rm (}atime, mtime{\rm )}}
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Set the access and modified time of the file to the given values.
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(The second argument is a tuple of two items.)
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\end{funcdesc}
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\begin{funcdesc}{wait}{}
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Wait for completion of a child process, and return a tuple containing
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its pid and exit status indication: a 16-bit number, whose low byte is
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the signal number that killed the process, and whose high byte is the
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exit status (if the signal number is zero); the high bit of the low
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byte is set if a core file was produced. (Not on MS-DOS.)
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\end{funcdesc}
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\begin{funcdesc}{waitpid}{pid\, options}
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Wait for completion of a child process given by proces id, and return
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a tuple containing its pid and exit status indication (encoded as for
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\code{wait()}). The semantics of the call are affected by the value of
|
|
the integer options, which should be 0 for normal operation. (If the
|
|
system does not support \code{waitpid()}, this always raises
|
|
\code{posix.error}. Not on MS-DOS.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{write}{fd\, str}
|
|
Write the string \var{str} to file descriptor \var{fd}.
|
|
Return the number of bytes actually written.
|
|
|
|
Note: this function is intended for low-level I/O and must be applied
|
|
to a file descriptor as returned by \code{posix.open()} or
|
|
\code{posix.pipe()}. To write a ``file object'' returned by the
|
|
built-in function \code{open} or by \code{posix.popen} or
|
|
\code{posix.fdopen}, or \code{sys.stdout} or \code{sys.stderr}, use
|
|
its \code{write()} method.
|
|
\end{funcdesc}
|
|
|
|
\begin{datadesc}{WNOHANG}
|
|
The option for \code{waitpid()} to avoid hanging if no child process
|
|
status is available immediately.
|
|
\end{datadesc}
|
|
|
|
|
|
\begin{datadesc}{O_RDONLY}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_WRONLY}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_RDWR}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_NDELAY}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_NONBLOCK}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_APPEND}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_DSYNC}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_RSYNC}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_SYNC}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_NOCTTY}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_CREAT}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_EXCL}
|
|
\end{datadesc}
|
|
\begin{datadesc}{O_TRUNC}
|
|
Options for the \code{flag} argument to the \code{open()} function.
|
|
These can be bit-wise OR'd together.
|
|
\end{datadesc}
|