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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 .
A regex search scans the text of each page on Wikipedia in real time, character by character, to find pages that match a specific sequence or pattern of characters. Unlike keyword searching, regex searching is by default case-sensitive, does not ignore punctuation, and operates directly on the page source (MediaWiki markup) rather than on the ...
Rather than use the search box, where entering an equals sign and a pipe character, and "quotes around phrases" is a straightforward matter, it is still easiest to use a regex-based search-link template — {{}} or {{}} — on the page with sample data, because then you can focus on the target data there and on writing the regexp pattern.
regex—Regular Expression; regexp—Regular Expression; RF—Radio Frequency; RFC—Request For Comments; RFI—Radio Frequency Interference; RFID—Radio Frequency Identification; RGB—Red, Green, Blue; RGBA—Red, Green, Blue, Alpha; RHL—Red Hat Linux; RHEL—Red Hat Enterprise Linux; REXX—Restructured Extended Executor Language; RIA ...
Then click on the "search and replace" icon on the right. In the popup form check the box for "Treat search string as a regular expression". Fill in the "Search for" box with (\|-\n\|) Fill in the "replace with" box with $1style=text-align:left| Then click "Replace all". All the text in the first column will be aligned to the left of their cells.
This is the "regular expression" (or regexp, or regex). Its metacharacters can represent multiple possibilities for a character position or a range of character positions within a page, using metacharacters for truth logic, grouping, counting, and modifying the characters to be found.
Regex experts should note that \n does not mean "newline," \d does not mean "digit," and so on: In MediaWiki syntax, the only use of \ is to escape metacharacters. / is special because it indicates the end of the regex. For example, insource:/yes/no/ is treated the same as insource:/yes/ no (because the keyword search for no/ ignores punctuation).
Greed, in regular expression context, describes the number of characters which will be matched (often also stated as "consumed") by a variable length portion of a regular expression – a token or group followed by a quantifier, which specifies a number (or range of numbers) of tokens. If the portion of the regular expression is "greedy", it ...