Regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters. With regular expressions, a technical editor may perform powerful search and replace techniques to transform data, such as reorganizing tables or removing particular data from documents in a single command.
regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters. Regular expressions (abbreviated as regex or regexp, with plural forms regexes, regexps, or regexen) are written in a formal language that can be interpreted by a regular expression processor, a program that either serves as a parser generator or examines text and identifies parts that match the provided specification.
Regular expressions, sometimes referred to as regex, grep, or pattern matching, can be a very powerful tool and a tremendous time-saver with a broad range of application. As an extended form of find-and-replace, you can use a regular expression to do things such as perform client-side validation of email addresses and phone numbers, search multiple documents for strings and patterns you wish to change or remove, or extract a list of links from source code. Regex is supported by most languages and tools, but because there can be varying implementations, this article will cover basic principles that are commonly used.
Basically, a regular expression is a pattern describing a certain amount of text. Their name comes from the mathematical theory on which they are based. In this tutorial, I will teach you all you need to know to be able to craft powerful time-saving regular expressions. I will start with the most basic concepts, so that you can follow this tutorial even if you know nothing at all about regular expressions yet.
There is no gentle beginning to regular expressions. You are either into hieroglyphics big time - in which case you will love this stuff - or you need to use them in which case a headache may be your only reward.
Virtually all non-trivial problems require you to filter good data from bad. Discover the many UNIX command line utilities that use regular expressions to discern the relevant from the irrelevant.
Regular expressions figure into all kinds of text-manipulation tasks. Searching and search-and-replace are among the more common uses, but regular expressions can also be used to test for certain conditions in a text file or data stream. You might use regular expressions, for example, as the basis for a short program that separates incoming mail from incoming spam.