Regular Expressions

Introduction

Introduction

• Often shortened to regex or regexp (pronounced the way it looks)
• Regular expressions are written like algebra for words, using symbols in addition to "literal" characters
• Can look for letters, numbers, and characters, including whitespace
• Can set up logical operations like "if the first character in a word is a number, look to see if the last character in the word is a number"
• Used in web design for simple search engines and checking that inputs are formatted correctly
• Used in programming to find specific parts of a file to modify or use in a program

Definitions

• A "string" is a set of characters, any characters
• The thing we're looking for, whether it's a phrase or word or set of numbers, is called the "target string"
• The thing you're searching, usually text files, is called the "source"
• And the regular expression we write is the "search string"
• A regex search string is correct if it finds all of the examples of the target string in the source
• A regex search string is incorrect if it only finds some of the target strings or none of them or finds the wrong string
• A program uses the search string as definition to find the target string and do something to or with it