Alastair's Axioms » RegEx

Regular expressions make my head hurt

Alastair — Tue, 22 Jan 2008 20:58:57 +0000

A site to dull the pain Rubular. Via Ruby Inside.

Mask Credit Card Numbers with Regular Expressions in Rails

Alastair — Thu, 14 Sep 2006 17:03:39 +0000

Sometimes you need to display sensitive information in a browser, such as the credit card a customer has on file. Obviously you don’t want to show the entire card number in case the customer leaves there browser open on a public computer, or even worse someone hacks into their account. However, you do need to show a piece of the information otherwise the customer would have no idea which credit card was on file. How to mask the credit card number? Regular Expressions to the rescue!

When I first searched for a way to do this I was surprised that I couldn’t find any examples, there’s a ton of regex tutorials for checking if emails are valid but none for masking credit card numbers. Here’s my solution in Rails.

Let’s say the customer’s card number is 5555-4444-3333-2222 (@customer.card_number = 5555-4444-3333-2222). First strip everything but the numbers.

    card_masked ||= @customer.card_number.gsub(/[^0-9]/, '')

Then mask all but the last four digits.

    @card_masked = card_masked.sub(/^([0-9]+)([0-9]{4})$/) { '*' * $1.length + $2 }

That’s it! @card_masked will out put as ************2222

Rails validation make sure your user passwords are strong

Alastair — Sat, 12 Aug 2006 17:04:33 +0000

Most user created passwords are astoundingly weak (’12345′, ‘mypass’). How do you make them stronger? Don’t give them a choice!

Here’s how to validate a password in RoR to make sure it’s strong using a regular expression (regex).
In your model add a custom validate method (after the regular validation) that adds an error unless the password is valid.

The ‘password_validate?’ method

def password_valid? self.password =~ /^(?=.*d)(?=.*[a-z])(?=.*[A-Z])(?!.*s).{8,15}$/ end

In this case the regular expression /^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?!.*\s).{8,15}$/ is checking that the password is 8-15 characters long ‘.{8,15}’, and it contains at least one uppercase letter ‘(?=.*[A-Z])’ and one digit ‘(?=.*\d)’. Actually it also checks for at least one lowercase letter as well ‘(?=.*[a-z])’ but most users usually include that, it also checks that there’s no funky characters ‘(?!.*\s)’