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:mod:`shlex` --- Simple lexical analysis
========================================
.. module:: shlex
:synopsis: Simple lexical analysis for Unix shell-like languages.
.. moduleauthor:: Eric S. Raymond <esr@snark.thyrsus.com>
.. moduleauthor:: Gustavo Niemeyer <niemeyer@conectiva.com>
.. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com>
.. sectionauthor:: Gustavo Niemeyer <niemeyer@conectiva.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, (for example, in run control files for Python
applications) or for parsing quoted strings.
.. note::
The :mod:`shlex` module currently does not support Unicode input.
The :mod:`shlex` module defines the following functions:
.. function:: split(s[, comments[, posix]])
Split the string *s* using shell-like syntax. If *comments* is :const:`False`
(the default), the parsing of comments in the given string will be disabled
(setting the :attr:`commenters` member of the :class:`shlex` instance to the
empty string). This function operates in POSIX mode by default, but uses
non-POSIX mode if the *posix* argument is false.
.. versionadded:: 2.3
.. versionchanged:: 2.6
Added the *posix* parameter.
.. note::
Since the :func:`split` function instantiates a :class:`shlex` instance, passing
``None`` for *s* will read the string to split from standard input.
The :mod:`shlex` module defines the following class:
.. class:: shlex([instream[, infile[, posix]]])
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-/stream-like object with :meth:`read` and
:meth:`readline` methods, or a string (strings are accepted since Python 2.3).
If no argument is given, input will be taken from ``sys.stdin``. The second
optional argument is a filename string, which sets the initial value of the
:attr:`infile` member. If the *instream* argument is omitted or equal to
``sys.stdin``, this second argument defaults to "stdin". The *posix* argument
was introduced in Python 2.3, and defines the operational mode. When *posix* is
not true (default), the :class:`shlex` instance will operate in compatibility
mode. When operating in POSIX mode, :class:`shlex` will try to be as close as
possible to the POSIX shell parsing rules.
.. seealso::
Module :mod:`ConfigParser`
Parser for configuration files similar to the Windows :file:`.ini` files.
.. _shlex-objects:
shlex Objects
-------------
A :class:`shlex` instance has the following methods:
.. method:: shlex.get_token()
Return a token. If tokens have been stacked using :meth:`push_token`, pop a
token off the stack. Otherwise, read one from the input stream. If reading
encounters an immediate end-of-file, :attr:`self.eof` is returned (the empty
string (``''``) in non-POSIX mode, and ``None`` in POSIX mode).
.. method:: shlex.push_token(str)
Push the argument onto the token stack.
.. method:: shlex.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.)
.. method:: shlex.sourcehook(filename)
When :class:`shlex` detects a source request (see :attr:`source` below) this
method is given the following token as argument, and expected to return a tuple
consisting of a filename and an open file-like object.
Normally, this method first strips any quotes off the argument. If the result
is an absolute pathname, or there was no previous source request in effect, or
the previous source was a stream (such as ``sys.stdin``), the result is left
alone. Otherwise, if the result is a relative pathname, the directory part of
the name of the file immediately before it on the source inclusion stack is
prepended (this behavior is like the way the C preprocessor handles ``#include
"file.h"``).
The result of the manipulations is treated as a filename, and returned as the
first component of the tuple, with :func:`open` called on it to yield the second
component. (Note: this is the reverse of the order of arguments in instance
initialization!)
This hook 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 :meth:`close`
method of the sourced input stream when it returns EOF.
For more explicit control of source stacking, use the :meth:`push_source` and
:meth:`pop_source` methods.
.. method:: shlex.push_source(stream[, filename])
Push an input source stream onto the input stack. If the filename argument is
specified it will later be available for use in error messages. This is the
same method used internally by the :meth:`sourcehook` method.
.. versionadded:: 2.1
.. method:: shlex.pop_source()
Pop the last-pushed input source from the input stack. This is the same method
used internally when the lexer reaches EOF on a stacked input stream.
.. versionadded:: 2.1
.. method:: shlex.error_leader([file[, 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 :mod:`shlex` users to generate error
messages in the standard, parseable format understood by Emacs and other Unix
tools.
Instances of :class:`shlex` subclasses have some public instance variables which
either control lexical analysis or can be used for debugging:
.. attribute:: shlex.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
``'#'`` by default.
.. attribute:: shlex.wordchars
The string of characters that will accumulate into multi-character tokens. By
default, includes all ASCII alphanumerics and underscore.
.. attribute:: shlex.whitespace
Characters that will be considered whitespace and skipped. Whitespace bounds
tokens. By default, includes space, tab, linefeed and carriage-return.
.. attribute:: shlex.escape
Characters that will be considered as escape. This will be only used in POSIX
mode, and includes just ``'\'`` by default.
.. versionadded:: 2.3
.. attribute:: shlex.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.
.. attribute:: shlex.escapedquotes
Characters in :attr:`quotes` that will interpret escape characters defined in
:attr:`escape`. This is only used in POSIX mode, and includes just ``'"'`` by
default.
.. versionadded:: 2.3
.. attribute:: shlex.whitespace_split
If ``True``, tokens will only be split in whitespaces. This is useful, for
example, for parsing command lines with :class:`shlex`, getting tokens in a
similar way to shell arguments.
.. versionadded:: 2.3
.. attribute:: shlex.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.
.. attribute:: shlex.instream
The input stream from which this :class:`shlex` instance is reading characters.
.. attribute:: shlex.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 :meth:`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.
.. attribute:: shlex.debug
If this member is numeric and ``1`` or more, a :class:`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.
.. attribute:: shlex.lineno
Source line number (count of newlines seen so far plus one).
.. attribute:: shlex.token
The token buffer. It may be useful to examine this when catching exceptions.
.. attribute:: shlex.eof
Token used to determine end of file. This will be set to the empty string
(``''``), in non-POSIX mode, and to ``None`` in POSIX mode.
.. versionadded:: 2.3
.. _shlex-parsing-rules:
Parsing Rules
-------------
When operating in non-POSIX mode, :class:`shlex` will try to obey to the
following rules.
* Quote characters are not recognized within words (``Do"Not"Separate`` is
parsed as the single word ``Do"Not"Separate``);
* Escape characters are not recognized;
* Enclosing characters in quotes preserve the literal value of all characters
within the quotes;
* Closing quotes separate words (``"Do"Separate`` is parsed as ``"Do"`` and
``Separate``);
* If :attr:`whitespace_split` is ``False``, any character not declared to be a
word character, whitespace, or a quote will be returned as a single-character
token. If it is ``True``, :class:`shlex` will only split words in whitespaces;
* EOF is signaled with an empty string (``''``);
* It's not possible to parse empty strings, even if quoted.
When operating in POSIX mode, :class:`shlex` will try to obey to the following
parsing rules.
* Quotes are stripped out, and do not separate words (``"Do"Not"Separate"`` is
parsed as the single word ``DoNotSeparate``);
* Non-quoted escape characters (e.g. ``'\'``) preserve the literal value of the
next character that follows;
* Enclosing characters in quotes which are not part of :attr:`escapedquotes`
(e.g. ``"'"``) preserve the literal value of all characters within the quotes;
* Enclosing characters in quotes which are part of :attr:`escapedquotes` (e.g.
``'"'``) preserves the literal value of all characters within the quotes, with
the exception of the characters mentioned in :attr:`escape`. The escape
characters retain its special meaning only when followed by the quote in use, or
the escape character itself. Otherwise the escape character will be considered a
normal character.
* EOF is signaled with a :const:`None` value;
* Quoted empty strings (``''``) are allowed;
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