# Introduction to Regular Expressions

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Information about Introduction to Regular Expressions
Technology

Published on August 19, 2009

Author: mattcasto

Source: slideshare.net

## Description

^Regular Expressions is one of those tools that every developer should have in their toolbox. You can do your job without regular expressions, but knowing when and how to use them will make you a much more efficient and marketable developer. You'll learn how regular expressions can be used for validating user input, parsing text, and refactoring code. We'll also cover various tools that can be used to help you write and share 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&apos;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

 User name: Comment:

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