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Algebraic laws for regular expressions can be obtained using a method by Gischer which is best explained along an example: In order to check whether (X+Y) * and (X * Y *) * denote the same regular language, for all regular expressions X, Y, it is necessary and sufficient to check whether the particular regular expressions (a+b) * and (a * b ...
Fuzzy Regular Expressions for Java: Java: LGPL GLib/GRegex [Note 3] GLib reference manual: C: LGPL GNU regex Gnulib reference manual: C LGPL GNU libc, GNU programs GRETA Microsoft Research: C++ Proprietary Gregex: Grovf Inc. RTL, HLS Proprietary: FPGA accelerated >100 Gbit/s regex engine for cybersecurity, financial, e-commerce industries ...
Self-validation: [19] re2c has a special mode in which it ignores all used-defined interface code and generates a self-contained skeleton program. Additionally, re2c generates two files: one with the input strings derived from the regular grammar, and one with compressed match results that are used to verify lexer behavior on all inputs.
In regular expressions, the period (., also called "dot") is the wildcard pattern which matches any single character. Combined with the asterisk operator .* it will match any number of any characters. In this case, the asterisk is also known as the Kleene star.
RELAX NG compact syntax is a non-XML format inspired by extended Backus–Naur form and regular expressions, designed so that it can be unambiguously translated to its XML counterpart, and back again, with one-to-one correspondence in structure and meaning, in much the same way that Simple Outline XML (SOX) relates to XML.
Ragel's input is a regular expression only in the sense that it describes a regular language; it is usually not written in a concise regular expression, but written out into multiple parts like in Extended Backus–Naur form. For example, instead of supporting POSIX character classes in regex syntax, Ragel implements them as built-in production ...
A basic example of string searching is when the pattern and the searched text are arrays of elements of an alphabet Σ. Σ may be a human language alphabet, for example, the letters A through Z and other applications may use a binary alphabet (Σ = {0,1}) or a DNA alphabet (Σ = {A,C,G,T}) in bioinformatics .
In the case of a web application, the programmer may use the same regular expression to validate input on both the client and the server side of the system. An attacker could inspect the client code, looking for evil regular expressions, and send crafted input directly to the web server in order to hang it.