10 Facts About Regular expressions

Regular expressions expression is a sequence of characters that specifies a search pattern in text.

Concept of regular expressions began in the 1950s, when the American mathematician Stephen Cole Kleene formalized the concept of a regular language.

Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another, widely used, being the Perl syntax.

Regular expressions are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis.

Regular expressions originated in 1951, when mathematician Stephen Cole Kleene described regular languages using his mathematical notation called regular events.

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Regular expressions entered popular use from 1968 in two uses: pattern matching in a text editor and lexical analysis in a compiler.

Regular expressions later added this capability to the Unix editor ed, which eventually led to the popular search tool grep's use of regular expressions .

Around the same time when Thompson developed QED, a group of researchers including Douglas T Ross implemented a tool based on regular expressions that is used for lexical analysis in compiler design.

Many variations of these original forms of regular expressions were used in Unix programs at Bell Labs in the 1970s, including vi, lex, sed, AWK, and expr, and in other programs such as Emacs.

Regular expressions consist of constants, which denote sets of strings, and operator symbols, which denote operations over these sets.