RegularExpressions

Make complex data searches easy(-ish)!

Mandi Grant@wygrant 9/9/2014

Regular expressions are forfinding text that conforms

to a particular pattern.

Short Examples

[bB]acon“Bacon” and “bacon” but not “BACON”d{5}5-digits in a row\b\.[a-z]{3}\b‘.’ followed by 3-letters (.com)

Let’s do something practical.

Example 1:

Validating a Social Security Number

nnn-nn-nnnn

In JavaScript, you can assign a regex to a var:

var regex = /\d{3}-\d{2}-\d{4}$/

JS Example

Let’s do a harder one!

Identify .txt files that contain at least one e-mail address.

Example 2:

Searching through Files

e-mail addresses are basically:

*@*.*

[a-zA-Z0-9.]\+@

[a-zA-Z0-9.] means “find any character between a- z, A-Z, and 0-9, and also allow ‘.’ ”

\+ means “accept any number of those things”

@ means “must include this symbol ‘@’ ”

Okay, what do we do with that?

Grep to the rescue!

$ grep is built in to Unix

Add arguments like -l to limit results to filenamesand > “output.txt” to pipe results to a file.

Our complete regular expression:

$ grep [a-zA-Z0-9.]\+@[a-zA-Z0-9.]\+\.[a-zA-Z0-9]{\2,20\} files/*

Run in command

line

Again forthe

domain

Look for any quantity of

these characters TLD

Must include

“@”

Must include

“.”

Between 2 and 20

characters long

notice there is no “.” in the TLD character set!

Searchfiles/*

Practical Uses for RegEx● Search 50k files for phone numbers

o Famous real-life problem Amazon faced in 2003● Change thousands of art asset filepaths

o We almost made some junior dev do this by hand...● Remove HTML tags, scripts in form data

o No l337 hax 4 u

RegEx Gotchas1. Data must fit a pattern2. Simplicity vs accuracy3. Be careful with

“optional” 4. Syntax varies by

environment

Try it out!regexr.com

...that match this very specific format:[a-zA-Z0-9.]\+@[a-zA-Z0-9.]\+\.[a-zA-Z0-9]{2,20}

Regular Expressions: