For example, I just started using Awesome Print in IRB. However, when I ran rails console , this error occurred:

no such file to load -- ap

After searching Google, I learned that Awesome Print needs to be listed in my Gemfile . Easy enough:

## ~/.irbrc
require 'rubygems'
require 'ap'

## ~/src/rails_3_app/Gemfile
group :development do
  gem 'awesome_print'
end

Sometimes, there’re restrictions on what patterns you can use. I wanted to change a regex for validating passwords. Originally, it allowed letters, numbers, and a seemingly random collection of special characters. How lame is this?:

^[A-Za-z0-9]{1}[A-Za-z0-9_\\.\\!\@\#\-]{0,255}$

Not only are the allowed special characters arbitrary, but they’re escaping characters in a character class, and using “{1}”.

I tried changing the regex to this:

^[[:print:]]{0,255}$

Unfortunately, that wasn’t considered “valid” by the system in question. Luckily, there’s a fairly concise alternative:

^[\x20-\x7E]{0,255}$

If you find a system that lacks support for POSIX character classes, check out this Wikipedia article.