.. _regex:

Regular Expression Syntax
=========================

Currently OSSEC supports two regex syntaxes:

* OS_Regex or regex
* OS_Match or sregex



.. _os_regex:

OS_Regex/regex Syntax
---------------------

Fast and simple library for regular expressions in C.

This library is designed to be simple, but support the most common regular
expressions. It was designed with intrusion detection systems in mind, where
having all options is not crucial, but speed is.

.. _os_regex_exp:

**Supported expressions**::

    \w  ->  A-Z, a-z, 0-9, '-', '@' characters
    \d  ->  0-9 characters
    \s  ->  For spaces " "
    \t  ->  For tabs.
    \p  ->  ()*+,-.:;<=>?[]!"'#$%&|{} (punctuation characters)
    \W  ->  For anything not \w
    \D  ->  For anything not \d
    \S  ->  For anything not \s
    \.  ->  For anything

.. _os_regex_mod:

**Modifiers**::

    +  ->  To match one or more times (eg \w+ or \d+)
    *  ->  To match zero or more times (eg \w* or \p*)

.. _os_regex_schar:

**Special Characters**::

    ^ -> To specify the beginning of the text.
    $ -> To specify the end of the text.
    | -> To create an "OR" between multiple patterns.

.. _os_regex_escape:

**Characters Escaping**

To utilize the following characters they must be escaped::

    $ -> \$
    ( -> \(
    ) -> \)
    \ -> \\
    | -> \|


.. _os_match:

OS_Match/sregex Syntax
----------------------

Faster than the OS_Regex/regex, but only supports simple string matching and the
following special characters.

.. _os_match_schar:

**Special Characters**::

    ^ -> To specify the beginning of the text.
    $ -> To specify the end of the text.
    | -> To create an "OR" between multiple patterns.