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Regular Expression Flavor Comparison – Detailed comparison of the most popular regular expression flavors; Regexp Syntax Summary; Online Regular Expression Testing – with support for Java, JavaScript, .Net, PHP, Python and Ruby; Implementing Regular Expressions – series of articles by Russ Cox, author of RE2; Regular Expression Engines
A regular expression (shortened as regex or regexp), [1] sometimes referred to as rational expression, [2] [3] is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings , or for input validation .
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
Some programming languages are case-sensitive for their identifiers (C, C++, Java, C#, Verilog, [2] Ruby, [3] Python and Swift).Others are case-insensitive (i.e., not case-sensitive), such as ABAP, Ada, most BASICs (an exception being BBC BASIC), Common Lisp, Fortran, SQL (for the syntax, and for some vendor implementations, e.g. Microsoft SQL Server, the data itself) [NB 2] Pascal, Rexx and ...
Snake case (sometimes stylized autologically as snake_case) is the naming convention in which each space is replaced with an underscore (_) character, and words are written in lowercase. It is a commonly used naming convention in computing , for example for variable and subroutine names, and for filenames .
insource:/regexp/ insource:/regexp/i: These are regular expressions. They use a lot of processing power, so we can only allow a few at a time on the search cluster, but they are very powerful. The version with the extra i runs the expression case-insensitive, and is even less efficient. Regex searches are likely to time out unless you further ...
Each regular expression is associated with a production rule in the lexical grammar of the programming language that evaluates the lexemes matching the regular expression. These tools may generate source code that can be compiled and executed or construct a state transition table for a finite-state machine (which is plugged into template code ...
Note that for non-pathological regular expressions, the problematic algorithms are usually fast, and in practice, one can expect them to "compile" a regex in O(m) time and match it in O(n) time; instead, simulation of an NFA and lazy computation of the DFA have O(m 2 n) worst-case complexity. [a] Regex denial of service occurs when these ...