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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 metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression (regex) engine.. In POSIX extended regular expressions, there are 14 metacharacters that must be escaped — preceded by a backslash (\) — in order to drop their special meaning and be treated literally inside an expression: opening and closing square brackets ...
The question mark? (also known as interrogation point, query, ... In the POSIX syntax for regular expressions, such as that used in Perl and Python, ...
Inverted question and exclamation marks ¡ Inverted exclamation mark: Exclamation mark, Interrobang ¿ Inverted question mark: Question mark, Interrobang < Less-than sign: Angle bracket, Chevron, Guillemet Lozenge: Square lozenge ("Pillow") ☞ Manicule: Index, Obelus: º: Masculine ordinal indicator: Feminine ordinal indicator, Degree sign ...
Python: python.org: Python Software Foundation License: Python has two major implementations, the built in re and the regex library. Ruby: ruby-doc.org: GNU Library General Public License: Ruby 1.8, Ruby 1.9, and Ruby 2.0 and later versions use different engines; Ruby 1.9 integrates Oniguruma, Ruby 2.0 and later integrate Onigmo, a fork from ...
If the portion of the regular expression is "greedy", it will match as many characters as possible. If it is not greedy, it will match as few characters as possible. By default, quantifiers in AWB are greedy. To make a quantifier non-greedy, it must be followed by a question mark. For example: In this string:
In SQL, wildcard characters can be used in LIKE expressions; the percent sign % matches zero or more characters, and underscore _ a single character. Transact-SQL also supports square brackets ([and ]) to list sets and ranges of characters to match, a leading caret ^ negates the set and matches only a character not within the list.
A string literal or anonymous string is a literal for a string value in the source code of a computer program. Modern programming languages commonly use a quoted sequence of characters, formally "bracketed delimiters", as in x = "foo", where , "foo" is a string literal with value foo.