UNIX for Dummies Questions & Answers

A couple co-workers have a disagreement. Can you guys please settle this?

One co-worker says regular expressions can inherently search and replace. His argument is that he can do a s/ regexp / replace in perl (and many other languages).

The other says that by definition regular expressions is just pattern matching and that is an outside function doing the replacing.

Thoughts?

Regular Expressions are just patterns...They do not perform any functions...It is the commands like sed or tr that we use along with the regular expression performs the functions like substitute/translate the pattern matched.

Its just my thought!

Concur, the substitution facility is not part of the regular expression formalism proper.

The original implementation of regular expressions was by Ken Thompson in the QED (and later ed) editor. Certainly, there was the s/re/p command in that already then, but his paper on regular expressions describes the "search" part and the underlying mathematical formalism, a concept called "regular sets" which is where the "regular" part in the name comes from.

Ken Thompson - Wikipedia, the free encyclopedia
Regular expression - Wikipedia, the free encyclopedia

K. Thompson, Regular Expression Search Algorithm, Comm. Assoc. Comp. Mach., Vol. 11, 6, pp. 419--422, 1968.

(It's the very first article in his publications list at http://www.cs.bell-labs.com/cm/cs/bib2html/ken.htm)