\section{Standard Module \sectcode{os}}

\stmodindex{os}
This module provides a more portable way of using operating system
(OS) dependent functionality than importing an OS dependent built-in
module like \code{posix}.

When the optional built-in module \code{posix} is available, this
module exports the same functions and data as \code{posix}; otherwise,
it searches for an OS dependent built-in module like \code{mac} and
exports the same functions and data as found there.  The design of all
Python's built-in OS dependen modules is such that as long as the same
functionality is available, it uses the same interface; e.g., the
function \code{os.stat(\var{file})} returns stat info about a \var{file} in a
format compatible with the POSIX interface.

Extensions peculiar to a particular OS are also available through the
\code{os} module, but using them is of course a threat to portability!

Note that after the first time \code{os} is imported, there is \emph{no}
performance penalty in using functions from \code{os} instead of
directly from the OS dependent built-in module, so there should be
\emph{no} reason not to use \code{os}!

In addition to whatever the correct OS dependent module exports, the
following variables and functions are always exported by \code{os}:

\renewcommand{\indexsubitem}{(in module os)}
\begin{datadesc}{name}
The name of the OS dependent module imported, e.g. \code{'posix'} or
\code{'mac'}.
\end{datadesc}

\begin{datadesc}{path}
The corresponding OS dependent standard module for pathname
operations, e.g., \code{posixpath} or \code{macpath}.  Thus, (given
the proper imports), \code{os.path.split(\var{file})} is equivalent to but
more portable than \code{posixpath.split(\var{file})}.
\end{datadesc}

\begin{datadesc}{curdir}
The constant string used by the OS to refer to the current directory,
e.g. \code{'.'} for POSIX or \code{':'} for the Mac.
\end{datadesc}

\begin{datadesc}{pardir}
The constant string used by the OS to refer to the parent directory,
e.g. \code{'..'} for POSIX or \code{'::'} for the Mac.
\end{datadesc}

\begin{datadesc}{sep}
The character used by the OS to separate pathname components, e.g.
\code{'/'} for POSIX or \code{':'} for the Mac.  Note that knowing this
is not sufficient to be able to parse or concatenate pathnames---better
use \code{os.path.split()} and \code{os.path.join()}---but it is
occasionally useful.
\end{datadesc}

\begin{funcdesc}{execl}{path\, arg0\, arg1\, ...}
This is equivalent to a call to \code{os.execv} with an \var{argv}
of \code{[\var{arg0}, \var{arg1}, ...]}.
\end{funcdesc}

\begin{funcdesc}{execle}{path\, arg0\, arg1\, ...\, env}
This is equivalent to a call to \code{os.execve} with an \var{argv}
of \code{[\var{arg0}, \var{arg1}, ...]}.
\end{funcdesc}

\begin{funcdesc}{execlp}{path\, arg0\, arg1\, ...}
This is like \code{execl} but duplicates the shell's actions in
searching for an executable file in a list of directories.  The
directory list is obtained from \code{environ['PATH']}.
\end{funcdesc}

\begin{funcdesc}{execvp}{path\, arg0\, arg1\, ...}
\code{execvp} is for \code{execv} what \code{execlp} is for \code{execl}.
\end{funcdesc}