Doc/lib/libposix.tex

   1 \section{\module{posix} ---
   2          The most common \POSIX{} system calls}
   3
   4 \declaremodule{builtin}{posix}
   5   \platform{Unix}
   6 \modulesynopsis{The most common \POSIX\ system calls (normally used
   7                 via module \refmodule{os}).}
   8
   9
  10 This module provides access to operating system functionality that is
  11 standardized by the C Standard and the \POSIX{} standard (a thinly
  12 disguised \UNIX{} interface).
  13
  14 \strong{Do not import this module directly.}  Instead, import the
  15 module \refmodule{os}, which provides a \emph{portable} version of this
  16 interface.  On \UNIX, the \refmodule{os} module provides a superset of
  17 the \module{posix} interface.  On non-\UNIX{} operating systems the
  18 \module{posix} module is not available, but a subset is always
  19 available through the \refmodule{os} interface.  Once \refmodule{os} is
  20 imported, there is \emph{no} performance penalty in using it instead
  21 of \module{posix}.  In addition, \refmodule{os}\refstmodindex{os}
  22 provides some additional functionality, such as automatically calling
  23 \function{putenv()} when an entry in \code{os.environ} is changed.
  24
  25 The descriptions below are very terse; refer to the corresponding
  26 \UNIX{} manual (or \POSIX{} documentation) entry for more information.
  27 Arguments called \var{path} refer to a pathname given as a string.
  28
  29 Errors are reported as exceptions; the usual exceptions are given for
  30 type errors, while errors reported by the system calls raise
  31 \exception{error} (a synonym for the standard exception
  32 \exception{OSError}), described below.
  33
  34
  35 \subsection{Large File Support \label{posix-large-files}}
  36 \sectionauthor{Steve Clift}{clift@mail.anacapa.net}
  37 \index{large files}
  38 \index{file!large files}
  39
  40
  41 Several operating systems (including AIX, HPUX, Irix and Solaris)
  42 provide support for files that are larger than 2 Gb from a C
  43 programming model where \ctype{int} and \ctype{long} are 32-bit
  44 values. This is typically accomplished by defining the relevant size
  45 and offset types as 64-bit values. Such files are sometimes referred
  46 to as \dfn{large files}.
  47
  48 Large file support is enabled in Python when the size of an
  49 \ctype{off_t} is larger than a \ctype{long} and the \ctype{long long}
  50 type is available and is at least as large as an \ctype{off_t}. Python
  51 longs are then used to represent file sizes, offsets and other values
  52 that can exceed the range of a Python int. It may be necessary to
  53 configure and compile Python with certain compiler flags to enable
  54 this mode. For example, it is enabled by default with recent versions
  55 of Irix, but with Solaris 2.6 and 2.7 you need to do something like:
  56
  57 \begin{verbatim}
  58 CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
  59         ./configure
  60 \end{verbatim} % $ <-- bow to font-lock
  61
  62 On large-file-capable Linux systems, this might work:
  63
  64 \begin{verbatim}
  65 CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
  66         ./configure
  67 \end{verbatim} % $ <-- bow to font-lock
  68
  69
  70 \subsection{Module Contents \label{posix-contents}}
  71
  72
  73 Module \module{posix} defines the following data item:
  74
  75 \begin{datadesc}{environ}
  76 A dictionary representing the string environment at the time the
  77 interpreter was started. For example, \code{environ['HOME']} is the
  78 pathname of your home directory, equivalent to
  79 \code{getenv("HOME")} in C.
  80
  81 Modifying this dictionary does not affect the string environment
  82 passed on by \function{execv()}, \function{popen()} or
  83 \function{system()}; if you need to change the environment, pass
  84 \code{environ} to \function{execve()} or add variable assignments and
  85 export statements to the command string for \function{system()} or
  86 \function{popen()}.
  87
  88 \note{The \refmodule{os} module provides an alternate
  89 implementation of \code{environ} which updates the environment on
  90 modification.  Note also that updating \code{os.environ} will render
  91 this dictionary obsolete.  Use of the \refmodule{os} module version of
  92 this is recommended over direct access to the \module{posix} module.}
  93 \end{datadesc}
  94
  95 Additional contents of this module should only be accessed via the
  96 \refmodule{os} module; refer to the documentation for that module for
  97 further information.