Interesting Regex Character Classes (2024)

FAQs

What are the special character classes in regex? ›

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 -. The usual metacharacters are normal characters inside a character class, and do not need to be escaped by a backslash.

Overloaded syntax and context

Regular expressions use a small set of symbols, and so some of these symbols to double duty. For example, symbols take on different meanings inside and outside of character classes. (See point #4 here.) Extensions to the basic syntax are worse.

It provides a versatile way to find and manipulate patterns within strings, making it an essential tool for tasks like data validation, text processing, and data extraction. Knowing how to use regex effectively can greatly enhance your programming skills and streamline your development process.

The plus ( + ) is a quantifier that matches one or more occurrences of the preceding element. The plus is similar to the asterisk ( * ) in that many occurrences are acceptable, but unlike the asterisk in that at least one occurrence is required.

^(\w+) matches the beginning of a line and then one or more word characters. Encloses an expression that matches set of characters. [\s] matches a whitespace character or a digit. [a-z0-9] matches “a” through “z” and numbers “0” through “9”.

No, its a tool that has its applications. Most of the time using a regex is shorter than writing a matching code explicitly, some people consider that difficult to understand, but it is just a matter of getting used to it, e.g. in Perl RegEx is used quite often.

and the string to match is all HTML tags. Greedy search — will try to match the longest possible string. The above regex matches the whole string ( <h1>Hello World</h1> ) because by default Regular Expression uses the Greedy algorithm & hence it finds the longest match.

contains(String) is much faster than explicitly using Regex .

How long does it take to learn regex? ›

How long does it take to learn Regex? - Quora. There's a lot to regex if you want to learn it deeply. But you can learn enough to be useful in just a few minutes: most characters are literal.

They can be hard to understand and maintain, especially for complex or long patterns. They can also be prone to errors and bugs, such as typos, syntax errors, or unintended matches. Another disadvantage of regex is that they are not very efficient or scalable.

You could use \b[1-9][0-9]{3}\b to match a number between 1000 and 9999. \b[1-9][0-9]{2,4}\b matches a number between 100 and 99999.

A pipe character ( | ) is used in regular expressions to specify an OR condition. For example, A or B is expressed as A | B.

The asterisk ( * ) is a quantifier that applies to the preceding regular expression element. It specifies that the preceding element may occur zero or more times.

\Q and \E are respectively the start and end of a literal string in a regex literal; they instruct the regex engine to not interpret the text inbetween those two "markers" as regexes. For instance, in order to match two stars, you could have this in your regex: \Q**\E.

In regular expressions, square brackets ( [ ] ) are characters that have a special meaning of their own. Since they have a special meaning, you can call them "metacharacter". Square brackets help you to define a character set, which is a set of characters you want to match.

UTF-8 represents ASCII invariant characters a-z, A-Z, 0-9, and certain special characters such as ' @ , . + - = / * ( ) the same way that they are represented in ASCII. UTF-16 represents these characters as NX'00 nn ' , where X' nn ' is the representation of the character in ASCII.