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2020-06-13

Regular expressions

Regexp

In 1943, Warren McCulloch and Walter Pitts published a scientific paper, “The Logical Calculus of Ideas Underlying Nervous Activity,” in which they tried to understand brain function by modeling neurons. They didn’t know then that their work would have a huge impact on computer science. https://www.cs.cmu.edu/~./epxing/Class/10715/reading/McCulloch.and.Pitts.pdf

In 1951, American mathematician Stephen Cole Claney, in his paper “Representation of Events in Neural Networks and Finite Automata,” proved McCulloch and Pitts’ ideas and formalized the definition of a “regular language” – a formal language that can be described by a regular expression. https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM704.pdf

A little later, in 1968, Ken Thomson (coauthor of Go, by the way) published “Regular Expression Search Algorithm.” https://www.oilshell.org/archive/Thompson-1968.pdf

A regular expression is a pattern/pattern which defines the rules for finding (or replacing) a substring in a string.

Regular expressions can be used to:

  • find all character sequences of “cat” in any context, such as “cat”, “cattle”, “personification”;
  • find the word “cat” and replace it with “dog”;
  • find the word “cat” preceded by the word “Persian” or “Cheshire”;
  • remove from the text all sentences that mention the word “cat” or “dog”.

Websites for checking and testing regular expressions:

And to test your regular expression writing skills, I can advise:

Don’t forget two words of wisdom: “You have a problem. You decided to use regular expressions. Now you have two problems.” “When all you have is a Hammer, everything looks like a Nail”.