CODEWITHSUNDEEP
regex
user1424739
user1424739

Reputation: 13675

Is it possible to define a character class of ^ only?

[^] means negating an empty character class. But I'd like to specify a character class with only the character "^". Is it possible? Thanks.

https://www.regular-expressions.info/charclass.html

Upvotes: 0

Views: 63

Answers (2)

c1moore
c1moore

Reputation: 1867

To answer the question asked, yes, there is*. For metacharacters in a character class, you can just escape the metacharacter like you would escape any other metacharacter in a regex:

[\^]

Reference

Note that this is generally not necessary because there are so few characters that are considered meta characters in a character class. Just \, ], and ^.

However, since you're only specifying a single character in your character class, you can do the same thing without the square brackets.

\^

Reference

Also, escaping the ^ symbol in a character class is only necessary if it is the first character in the character class. If you had any additional characters, just add the ^ anywhere else and it will work as expected

[a-z^]

Reference

The above would match any lower-cased alphabetical Latin character or ^.

* There is an exception to this rule. If you are using a POSIX or GNU regex engine, you cannot escape metacharacters in a character class because the \ is not considered a metacharacter.

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. The POSIX and GNU flavors are an exception. They treat backslashes in character classes as literal characters. So with these flavors, you can't escape anything in character classes.

-- regular-expressions.info

Upvotes: 2

user52889
user52889

Reputation: 1501

If you want to create a character class containing only a caret, probably the two most straightforward ways are:

  • escape the caret: [\^]
  • refer to the caret by its character code: [\x5e] (which you might be more inclined to use if you are building a character class programatically and are worried about other metacharacters like backslash, hyphen or square brackets)

But a character class containing only one character is probably unnecessary. You can just use the caret outside the class: \^.

Escaping caret in character classes is only necessary at the start of the class, where it negates the class, but that clearly doesn't help you if it is the only character in the class.

Upvotes: 0

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