\section{\module{shlex} ---
         Simple lexical analysis}

\declaremodule{standard}{shlex}
\modulesynopsis{Simple lexical analysis for \UNIX{} shell-like languages.}
\moduleauthor{Eric S. Raymond}{esr@snark.thyrsus.com}
\sectionauthor{Eric S. Raymond}{esr@snark.thyrsus.com}

\versionadded{1.5.2}

The \class{shlex} class makes it easy to write lexical analyzers for
simple syntaxes resembling that of the \UNIX{} shell.  This will often
be useful for writing minilanguages, e.g.\ in run control files for
Python applications.

\begin{classdesc}{shlex}{\optional{stream}, \optional{file}}
A \class{shlex} instance or subclass instance is a lexical analyzer
object.  The initialization argument, if present, specifies where to
read characters from. It must be a file- or stream-like object with
\method{read()} and \method{readline()} methods.  If no argument is given,
input will be taken from \code{sys.stdin}.  The second optional 
argument is a filename string, which sets the initial value of the
\member{infile} member.  If the stream argument is omitted or
equal to \code{sys.stdin}, this second argument defauilts to ``stdin''.
\end{classdesc}


\begin{seealso}
  \seemodule{ConfigParser}{Parser for configuration files similar to the
                           Windows \file{.ini} files.}
\end{seealso}


\subsection{shlex Objects \label{shlex-objects}}

A \class{shlex} instance has the following methods:

\begin{methoddesc}{get_token}{}
Return a token.  If tokens have been stacked using
\method{push_token()}, pop a token off the stack.  Otherwise, read one
from the input stream.  If reading encounters an immediate
end-of-file, an empty string is returned. 
\end{methoddesc}

\begin{methoddesc}{push_token}{str}
Push the argument onto the token stack.
\end{methoddesc}

\begin{methoddesc}{read_token}{}
Read a raw token.  Ignore the pushback stack, and do not interpret source
requests.  (This is not ordinarily a useful entry point, and is
documented here only for the sake of completeness.)
\end{methoddesc}

\begin{methoddesc}{openhook}{filename}
When shlex detects a source request (see \member{source} below)
this method is given the following token as argument, and expected to 
return a tuple consisting of a filename and an opened stream object. 

Normally, this method just strips any quotes off the argument and
treats it as a filename, calling \code{open()} on it.  It is exposed so that
you can use it to implement directory search paths, addition of
file extensions, and other namespace hacks.

There is no corresponding `close' hook, but a shlex instance will call
the \code{close()} method of the sourced input stream when it returns EOF.
\end{methoddesc}

\begin{methoddesc}{error_leader}{\optional{file}, \optional{line}}
This method generates an error message leader in the format of a
Unix C compiler error label; the format is '"\%s", line \%d: ',
where the \%s is replaced with the name of the current source file and
the \%d with the current input line number (the optional arguments
can be used to override these).

This convenience is provided to encourage shlex users to generate
error messages in the standard, parseable format understood by Emacs
and other Unix tools.
\end{methoddesc}

Instances of \class{shlex} subclasses have some public instance
variables which either control lexical analysis or can be used
for debugging:

\begin{memberdesc}{commenters}
The string of characters that are recognized as comment beginners.
All characters from the comment beginner to end of line are ignored.
Includes just \character{\#} by default.   
\end{memberdesc}

\begin{memberdesc}{wordchars}
The string of characters that will accumulate into multi-character
tokens. By default, includes all \ASCII{} alphanumerics and
underscore.
\end{memberdesc}

\begin{memberdesc}{whitespace}
Characters that will be considered whitespace and skipped.  Whitespace
bounds tokens.  By default, includes space, tab, linefeed and
carriage-return.
\end{memberdesc}

\begin{memberdesc}{quotes}
Characters that will be considered string quotes.  The token
accumulates until the same quote is encountered again (thus, different
quote types protect each other as in the shell.)  By default, includes
\ASCII{} single and double quotes.
\end{memberdesc}

\begin{memberdesc}{infile}
The name of the current input file, as initially set at class
instantiation time or stacked by later source requests.  It may
be useful to examine this when constructing error messages.
\end{memberdesc}

\begin{memberdesc}{instream}
The input stream from which this shlex instance is reading characters.
\end{memberdesc}

\begin{memberdesc}{source}
This member is None by default.  If you assign a string to it, that
string will be recognized as a lexical-level inclusion request similar
to the `source' keyword in various shells.  That is, the immediately
following token will opened as a filename and input taken from that
stream until EOF, at which point the \code{close()} method of that
stream will be called and the input source will again become the
original input stream. Source requests may be stacked any number of
levels deep.
\end{memberdesc}

\begin{memberdesc}{debug}
If this member is numeric and 1 or more, a shlex instance will print
verbose progress output on its behavior.  If you need to use this,
you can read the module source code to learn the details.
\end{memberdesc}

Note that any character not declared to be a word character,
whitespace, or a quote will be returned as a single-character token.

Quote and comment characters are not recognized within words.  Thus,
the bare words \samp{ain't} and \samp{ain\#t} would be returned as single
tokens by the default parser.

\begin{memberdesc}{lineno}
Source line number (count of newlines seen so far plus one).
\end{memberdesc}

\begin{memberdesc}{token}
The token buffer.  It may be useful to examine this when catching
exceptions.
\end{memberdesc}
