Regular expression

정규표현식

History

The seeds of regular expressions were planted in the early 1940s by two neuro-physiologists, Warren McCulloch and Walter Pitts, who developed models of how they believed the nervous system worked at the neuron level. Regular expressions became a reality several years later when mathematician Stephen Kleene formally described these models in an algebra he called regular sets. He devised a simple notation to express these regular sets, and called them regular expressions.

Through the 1950s and 1960s, regular expressions enjoyed a rich study in theoretical mathematics circles. Robert Constable has written a good summary for the mathematically inclined.

Although there is evidence of earlier work, the first published computational use of regular expressions I have actually been able to find is Ken Thompson’s 1968 article “Regular Expression Search Algorithm” in which he describes a regular-expression compiler that produced IBM 7094 object code. This led to his work on qed, an editor that formed the basis for the Unix editor ed.

ed’s regular expressions were not as advanced as those in qed, but they were the first to gain widespread use in non-technical fields. ed had a command to display lines of the edited file that matched a given regular expression. The command, g/Regular Expression/p, was read “Global Regular Expression Print.” This particular function was so useful that it was made into its own utility, grep (after which egrep - extended grep - was later modeled). —Chapter 3, Mastering regular expressions

Tools

• debuggex.com/ - 정규식을 Finite state machine 유사한 형태로 시각화.