What is Regular expression (Regex)?

A regular expression, shortened as Regex, and referred to as a rational expression, is a sequence of characters that specifies a search pattern.

String-searching algorithms commonly use these patterns for “find” or “find and replace” operations on strings and input validation. They are used in search engine search-and-replace dialogs of word processors and text editors, in text processing utilities, and in lexical analysis.

Many programming languages provide regex capabilities that are either built-in or via libraries.

Regular expressions, also called patterns, specify sets of strings required for specific purposes.

The most simplistic way to specify a finite set of strings is to list its elements. However, there are often more concise ways: for example, the set containing the three strings “geschaft”, “geschäft”, and “geschaeft” can be specified by the pattern g(ä|ae?)ft; it can be said that this pattern matches each of the three strings.

What is Regex used for?

Regex is mainly used for text-based searching and string manipulation but is also widely used in web development, data science, natural language processing, and text analytics.

How does Regex work?

Regular expressions are a sequence of characters that specify search patterns.

Regex is written using a combination of special characters and literal characters. These special characters allow regular expressions to find patterns in strings, while the literal characters are used as exact matches for specific words or phrases.

For example:

  • Regex 9 matches “9”
  • Regex four|4 accepts strings “four” or “4”
  • Regex colou?r contains {color, colour}

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