Regular expression
A regular expression (abbreviated regexp or regex) is a way to describe sets of characters using syntactic rules.[1] Many programming languages use or support regular expressions. A regular expression is then used by a special program or part of a programming language. This program will either generate a parser that can be used to match expressions or it will match such expressions itself.
A regular expression processor is used for processing a regular expression statement in terms of a grammar in a given formal language, and with that examines a text string.
A few examples of what can be matched with regular expressions:
- The sequence of characters "car" appearing consecutively in any context, such as in "car", "cartoon", or "bicarbonate"
- The sequence of characters "car" occurring in that order with other characters between them, such as in "Icelander" or "chandler"
- The word "car" when it appears as an isolated word
- The word "car" when preceded by the word "blue" or "red"
- The word "car" when not preceded by the word "motor"
- A dollar sign immediately followed by one or more digits, and then optionally a period and exactly two more digits (for example, "$10" or "$245.99"). This does not match "$ 5", because of the space between the dollar sign and the digit, nor "€25", because there is no dollar sign.
Regular expressions can be much more complex than these examples. Many regular expression languages also support "wildcard" characters.
Regular Expression Media
Blue highlights show the match results of the regular expression pattern: /h[aeiou]+/g (the letter h followed by one or more vowels)
Stephen Cole Kleene, who introduced the concept
Translating the Kleene star(s* means "zero or more of s")
A blacklist on Wikipedia which uses regular expressions to identify bad titles
References
- ↑ "re — Regular expression operations — Python 3.8.3 documentation". docs.python.org. Retrieved 2020-05-17.
