Command one liners

I was fooling with some data using cut, sed, etc.   When I needed to sum up all of the numbers, I used to do this with a Perl script (years ago), but it's a one liner in Ruby now:

cat numbers | ruby -e 'puts ARGF.collect {|l| l.match(/^ *(\d+)/)[1].to_i}.inject(0, &:+)'

This uses the Ruby 1.9 ARGF feature and matches just the first number listed (possibly preceded by spaces), converts them to an array of integers, then sums them using Array#inject.

RVM and CRON with ruby PADRINO

When cron runs a job, the job has very little environment. In my installation, I use RVM to switch between different versions of ruby, and so trying to run any sort of cron job is difficult.

My recommendation is that you start out using a shell script which executes your ruby process. Here's one that works for me:

#!/bin/sh
. /usr/bin/rvm > /dev/null
rvm use ruby-1.9.3-p0

cd /wherever
export PADRINO_ENV=production
/usr/bin/time ./import-noc-events.rb
exit 0

cattr_accessor

When I was new to ruby and rails, I ran into cattr_accessor and it's lack of documentation.

Simply, cattr_accessor creates a class-level accessor for a class variable. It also adds an instance method for accessing the class variable. There are several options that can be specified to remove the instance_reader and instance_writer. Cattr_accessor is located in the file activesupport/lib/active_support/core_ext/class/attribute_accessors.rb.

These class variables are shared with any subclasses, so be carefull. For example -

Loading development environment (Rails 3.0.0.beta3)

irb(main):001:0> class Pet

irb(main):002:1> cattr_accessor :number

irb(main):003:1> end

=> [:number]

irb(main):004:0> class Dog <>

irb(main):005:1> end

=> nil

irb(main):006:0> class Cat <>

irb(main):007:1> end

=> nil

irb(main):008:0> Dog.class_eval('number = 4')

=> 4

irb(main):009:0> Cat.class_eval('number = 0')

=> 0

irb(main):010:0> puts Dog.class_eval('number')

0

=> nil

irb(main):011:0>

This is because the inherited accessors all reference the Pet's number.