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31 Dec 12
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n computing, a regular expression provides a concise and flexible means to "match" (specify and recognize) strings of text, such as particular characters, words, or patterns of characters. Common abbreviations for "regular expression" include regex and regexp.
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Most formalisms provide the following operations to construct regular expressions
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- Boolean "or"
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Grouping
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Quantification
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While regular expressions would be useful on Internet search engines, processing them across the entire database could consume excessive computer resources depending on the complexity and design of the regex. Although in many cases system administrators can run regex-based queries internally, most search engines do not offer regex support to the public. Notable exceptions: Google Code Search, Exalead.
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24 Apr 12
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06 Jan 11
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Regular expressions are used by many text editors, utilities, and programming languages to search and manipulate text based on patterns. Some of these languages, including Perl, Ruby, Awk, and Tcl, have fully integrated regular expressions into the syntax of the core language itself. Others like C, C++,.NET, Java, and Python instead provide access to regular expressions only through libraries. Utilities provided by Unix distributions—including the editor ed and the filter grep—were the first to popularize the concept of regular expressions.
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28 Apr 10
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Within POSIX bracket expressions, the dot character matches a literal dot. For example,
a.cmatches "abc", etc., but[a.c]matches only "a", ".", or "c". -
Matches a single character that is contained within the brackets. For example,
[abc]matches "a", "b", or "c".[a-z]specifies a range which matches any lowercase letter from "a" to "z". These forms can be mixed:[abcx-z]matches "a", "b", "c", "x", "y", or "z", as does[a-cx-z]. -
-character is treated as a literal character if it is the last or the first (after the^) -
[:space:]\s[ \t\r \v\f]Whitespace characters
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20 Apr 10
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31 Jul 08
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ero or one of the preceding element
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zero or more of the preceding element
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one or more of the preceding element
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any single character
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a single character that is contained within the brackets
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a single character that is not contained within the brackets
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starting position
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starting position
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ending position of the string
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14 Jun 05
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