Introduction to Regular Expressions

Introduction toRegular Expressions Matt Casto http://google.com/profiles/mattcasto

Introduction toRegular Expressions Matt Casto Quick Solutions http://google.com/profiles/mattcasto

“Some people, when confronted with a problem, think “I know, I'll use regular expressions. Now they have two problems.” - Jamie Zawinski, August 12, 1997



What are Regular Expressions? ^w+@[a-zA-Z_]+?.[a-zA-Z]{2,3}$ [w-]+@([w-]+.)+[w-]+ ^.+@[^.].*.[a-z]{2,}$ ^([a-zA-Z0-9_-.]+)@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.)|(([a-zA-Z0-9-]+.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(]?)$



History Stephen Cole Kleene American mathematician credited for inventing Regular Expressions in the 1950’s using a mathematic notation called regular sets.

History Ken Thompson American pioneer of computer science who, among many other things, used Kleene’s regular sets for searching in his QED and ed text editors.

History grep Global Regular Expression Print

History Henry Spencer Wrote the regex library which is what Perl and Tcl languages used for regular expressions.

Why Should You Care? Example: finding duplicate words in a file. Requirements: Output lines that contain duplicate words Find doubled words that expand lines Ignore capitalization differences Ignore HTML tags

Output lines that contain duplicate words

Find doubled words that expand lines

Ignore capitalization differences

Ignore HTML tags