![]() ![]() matches a dollar or euro sign, assuming your regex flavor supports Unicode escapes. For flavors that support Unicode, it also includes Unicode character escapes and Unicode properties. This includes character escapes, octal escapes, and hexadecimal escapes for non-printable characters. Many regex tokens that work outside character classes can also be used inside character classes. Regex flavors are quite inconsistent about this. Hyphens at other positions in character classes where they can’t form a range may be interpreted as literals or as errors. This works in all flavors discussed in this tutorial. and match any character that is not an x or a hyphen. The hyphen can be included right after the opening bracket, or right before the closing bracket, or right after the negating caret. So both JavaScript and Ruby require closing brackets to be escaped with a backslash to include them as literals in a character class. Ruby treats empty character classes as an error. This does not work in JavaScript, which treats as an empty character class that always fails to match, and as a negated empty character class that matches any single character. x ] matches any character that is not a closing bracket or an x. You can include an unescaped closing bracket by placing it right after the opening bracket, or right after the negating caret. This works with all flavors discussed in this tutorial. To include an unescaped caret as a literal, place it anywhere except right after the opening bracket. So with these flavors, you can’t escape anything in character classes. They treat backslashes in character classes as literal characters. The POSIX and GNU flavors are an exception. The closing bracket ], the caret ^ and the hyphen - can be included by escaping them with a backslash, or by placing them in a position where they do not take on their special meaning. To include a backslash as a character without any special meaning inside a character class, you have to escape it with another backslash. Your regex will work fine if you escape the regular metacharacters inside a character class, but doing so significantly reduces readability. The usual metacharacters are normal characters inside a character class, and do not need to be escaped by a backslash. In most regex flavors, the only special characters or metacharacters inside a character class are the closing bracket ], the backslash \, the caret ^, and the hyphen. If you want the regex to match the q, and only the q, in both strings, you need to use negative lookahead: q (?! u ). Indeed: the space becomes part of the overall match, because it is the “character that is not a u” that is matched by the negated character class in the above regexp. It does match the q and the space after the q in Iraq is a country. It does not match the q in the string Iraq. It means: “a q followed by a character that is not a u”. ![]() ![]() q does not mean: “a q not followed by a u”. It is important to remember that a negated character class still must match a character. matches any character that is not a digit or a line break. If you don’t want a negated character class to match line breaks, you need to include the line break characters in the class. Unlike the dot, negated character classes also match (invisible) line break characters. The result is that the character class matches any character that is not in the character class. Typing a caret after the opening square bracket negates the character class. You can find a C-style hexadecimal number with 0 +. You can find an identifier in a programming language with *. You can find a word, even if it is misspelled, such as sep r te or li en e. Again, the order of the characters and the ranges does not matter.Ĭharacter classes are one of the most commonly used features of regular expressions. matches a hexadecimal digit or the letter X. You can combine ranges and single characters. matches a single hexadecimal digit, case insensitively. You can use a hyphen inside a character class to specify a range of characters. The order of the characters inside a character class does not matter. gr y does not match graay, graey or any such thing. Very useful if you do not know whether the document you are searching through is written in American or British English.Ī character class matches only a single character. You could use this in gr y to match either gray or grey. ![]() Simply place the characters you want to match between square brackets. With a “character class”, also called “character set”, you can tell the regex engine to match only one out of several characters. ![]()
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