.. 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>
Source code: :source:`Lib/shlex.py`
The :class:`~shlex.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.
The :mod:`shlex` module defines the following functions:
.. function:: split(s, comments=False, posix=True) 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:`~shlex.commenters` attribute of the :class:`~shlex.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. .. note:: Since the :func:`split` function instantiates a :class:`~shlex.shlex` instance, passing ``None`` for *s* will read the string to split from standard input.
.. function:: quote(s)
Return a shell-escaped version of the string *s*. The returned value is a
string that can safely be used as one token in a shell command line, for
cases where you cannot use a list.
This idiom would be unsafe:
>>> filename = 'somefile; rm -rf ~'
>>> command = 'ls -l {}'.format(filename)
>>> print(command) # executed by a shell: boom!
ls -l somefile; rm -rf ~
:func:`quote` lets you plug the security hole:
>>> from shlex import quote
>>> command = 'ls -l {}'.format(quote(filename))
>>> print(command)
ls -l 'somefile; rm -rf ~'
>>> remote_command = 'ssh home {}'.format(quote(command))
>>> print(remote_command)
ssh home 'ls -l '"'"'somefile; rm -rf ~'"'"''
The quoting is compatible with UNIX shells and with :func:`split`:
>>> from shlex import split
>>> remote_command = split(remote_command)
>>> remote_command
['ssh', 'home', "ls -l 'somefile; rm -rf ~'"]
>>> command = split(remote_command[-1])
>>> command
['ls', '-l', 'somefile; rm -rf ~']
.. versionadded:: 3.3
The :mod:`shlex` module defines the following class:
A :class:`~shlex.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:`~io.TextIOBase.read` and :meth:`~io.TextIOBase.readline` methods, or
a string. 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:`~shlex.infile` attribute. If the instream
argument is omitted or equal to sys.stdin, this second argument
defaults to "stdin". The posix argument defines the operational mode:
when posix is not true (default), the :class:`~shlex.shlex` instance will
operate in compatibility mode. When operating in POSIX mode,
:class:`~shlex.shlex` will try to be as close as possible to the POSIX shell
parsing rules. The punctuation_chars argument provides a way to make the
behaviour even closer to how real shells parse. This can take a number of
values: the default value, False, preserves the behaviour seen under
Python 3.5 and earlier. If set to True, then parsing of the characters
();<>|& is changed: any run of these characters (considered punctuation
characters) is returned as a single token. If set to a non-empty string of
characters, those characters will be used as the punctuation characters. Any
characters in the :attr:`wordchars` attribute that appear in
punctuation_chars will be removed from :attr:`wordchars`. See
:ref:`improved-shell-compatibility` for more information.
.. versionchanged:: 3.6 The *punctuation_chars* parameter was added.
.. seealso:: Module :mod:`configparser` Parser for configuration files similar to the Windows :file:`.ini` files.
A :class:`~shlex.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:`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.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:`~io.IOBase.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(newstream, newfile=None) 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.
.. 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.
.. method:: shlex.error_leader(infile=None, lineno=None) 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.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. In POSIX mode, the accented characters in the Latin-1 set are also included. If :attr:`punctuation_chars` is not empty, the characters ``~-./*?=``, which can appear in filename specifications and command line parameters, will also be included in this attribute, and any characters which appear in ``punctuation_chars`` will be removed from ``wordchars`` if they are present there.
.. 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.
.. 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.
.. 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.shlex`, getting tokens in a similar way to shell arguments. If this attribute is ``True``, :attr:`punctuation_chars` will have no effect, and splitting will happen only on whitespaces. When using :attr:`punctuation_chars`, which is intended to provide parsing closer to that implemented by shells, it is advisable to leave ``whitespace_split`` as ``False`` (the default value).
.. 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.shlex` instance is reading characters.
.. attribute:: shlex.source This attribute 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 be opened as a filename and input will be taken from that stream until EOF, at which point the :meth:`~io.IOBase.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 attribute is numeric and ``1`` or more, a :class:`~shlex.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.
.. attribute:: shlex.punctuation_chars Characters that will be considered punctuation. Runs of punctuation characters will be returned as a single token. However, note that no semantic validity checking will be performed: for example, '>>>' could be returned as a token, even though it may not be recognised as such by shells. .. versionadded:: 3.6
When operating in non-POSIX mode, :class:`~shlex.shlex` will try to obey to the following rules.
Do"Not"Separate is
parsed as the single word Do"Not"Separate);"Do"Separate is parsed as "Do" and
Separate);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.shlex` will only
split words in whitespaces;'');When operating in POSIX mode, :class:`~shlex.shlex` will try to obey to the following parsing rules.
"Do"Not"Separate" is
parsed as the single word DoNotSeparate);'\') preserve the literal value of the
next character that follows;"'") preserve the literal value
of all characters within the quotes;'"') preserves the literal value
of all characters within the quotes, with the exception of the characters
mentioned in :attr:`~shlex.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.'') are allowed... versionadded:: 3.6
The :class:`shlex` class provides compatibility with the parsing performed by
common Unix shells like bash, dash, and sh. To take advantage of
this compatibility, specify the punctuation_chars argument in the
constructor. This defaults to False, which preserves pre-3.6 behaviour.
However, if it is set to True, then parsing of the characters ();<>|&
is changed: any run of these characters is returned as a single token. While
this is short of a full parser for shells (which would be out of scope for the
standard library, given the multiplicity of shells out there), it does allow
you to perform processing of command lines more easily than you could
otherwise. To illustrate, you can see the difference in the following snippet:
>>> import shlex
>>> text = "a && b; c && d || e; f >'abc'; (def \"ghi\")"
>>> list(shlex.shlex(text))
['a', '&', '&', 'b', ';', 'c', '&', '&', 'd', '|', '|', 'e', ';', 'f', '>',
"'abc'", ';', '(', 'def', '"ghi"', ')']
>>> list(shlex.shlex(text, punctuation_chars=True))
['a', '&&', 'b', ';', 'c', '&&', 'd', '||', 'e', ';', 'f', '>', "'abc'",
';', '(', 'def', '"ghi"', ')']
Of course, tokens will be returned which are not valid for shells, and you'll need to implement your own error checks on the returned tokens.
Instead of passing True as the value for the punctuation_chars parameter,
you can pass a string with specific characters, which will be used to determine
which characters constitute punctuation. For example:
>>> import shlex
>>> s = shlex.shlex("a && b || c", punctuation_chars="|")
>>> list(s)
['a', '&', '&', 'b', '||', 'c']
Note
When punctuation_chars is specified, the :attr:`~shlex.wordchars`
attribute is augmented with the characters ~-./*?=. That is because these
characters can appear in file names (including wildcards) and command-line
arguments (e.g. --color=auto). Hence:
>>> import shlex
>>> s = shlex.shlex('~/a && b-c --color=auto || d *.py?',
... punctuation_chars=True)
>>> list(s)
['~/a', '&&', 'b-c', '--color=auto', '||', 'd', '*.py?']
For best effect, punctuation_chars should be set in conjunction with
posix=True. (Note that posix=False is the default for
:class:`~shlex.shlex`.)
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