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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 .
In functional and list-based languages a string is represented as a list (of character codes), therefore all list-manipulation procedures could be considered string functions. However such languages may implement a subset of explicit string-specific functions as well.
The original Mozilla proxy auto-config implementation, which provides a glob-matching function on strings, uses a replace-as-RegExp implementation as above. The bracket syntax happens to be covered by regex in such an example. Python's fnmatch uses a more elaborate procedure to transform the pattern into a regular expression. [17]
Any amount of text can be matched by a regular expression. Languages that use this type of regular expression include Perl, Java, JavaScript, Python, Ruby, .NET, and XML. A list of the regular expressions accepted by this search and replace box has been compiled for reference by the Mozilla Contributors.
Function list: Lists all functions from current file in a window or sidebar and allows user to jump directly to the definition of that function for example by double-clicking on the function name in the list. More or less realtime (does not require creating a symbol database, see below).
This single element must be the first. The empty list would not match the pattern at all, as an empty list does not have a head (the first element that is constructed). In the example, we have no use for list, so we can disregard it, and thus write the function:
For example, in Python, raw strings are preceded by an r or R – compare 'C:\\Windows' with r'C:\Windows' (though, a Python raw string cannot end in an odd number of backslashes). Python 2 also distinguishes two types of strings: 8-bit ASCII ("bytes") strings (the default), explicitly indicated with a b or B prefix, and Unicode strings ...