Simon Rentzke

Blue Blistering Barnacles

Quickly setup a ruby on rails 5 app

Setup your app directory

mkdir rails-5-test-app
cd rails-5-test-app

Specify your Ruby version

touch .ruby-version
echo 'ruby-2.2.2' > .ruby-version

Setup Gemfile with edge rails, rack and arel

touch Gemfile
printf "source ''\nruby '2.2.2'\n\n\ngem 'rails', github: 'rails/rails'\ngem 'arel', github: 'rails/arel'\ngem 'rack', github: 'rack/rack'" >> Gemfile

Use rails generators to create new app, and run server

bundle exec rails new . --dev --force
bundle exec rails s

Just give me the gist?

Machines are learning from us, and that's not always a good thing

I was recently playing with Google's new Photo application. An incredibly powerful little application, yet has an incredibly simple UI.

Google has gone through my entire library of 30k photos and classified them against their boat loads of data.

It's always nice to get a visual sense of what Machine Learning is doing, and after playing with the photo app it's quite clear how it classifies photos.

For example, if I search for 'festival', it finds photo's of all sorts of festivals, from Glastonbury:


To the Soccer World Cup:

South Africa world cup

To the Notting Hill Carnival:

Notting Hill Carnival

To a few incorrect ones like these:


You can understand why machine learning might classify these, and it's not really a problem. When we have more data, those results will continue to get better, they will almost definitely result in more accuracy going into the future.

So, what's the problem?

The problem is here; do a search for something like 'desert', I get this result:

namibia desert

Do a search for 'dessert' and I get this result:

namibia desert

So, through our own stupidity, we have trained the machines to think 'dessert' is the same as 'desert'.

A trivial example, but in a time when we are ramping up our dependence on machine learning, we need to remember that the machine is not always correct and it is for the same reason as the crowd is not always correct.

Safety nets

I've had a few close calls when switching between the Dev/Staging/Prod environments. These will save you from any nasty suprises!

iTerm Colour

Change the colour of the terminal window when you ssh into your staging or production environments. I use a simple bash script that switches when I ssh into certain hosts.

Banner/Ribbon on Staging/Development

I just used a fork of the Github ribbon

Show App Name and Environment when in console

We used this handy gem Marco-Polo

That looks like this in the console:

~/Sites/myapp$ rails c

Ruby "&& vs and" , "or vs ||"

tl;dr && and || have higher precendence

Difference between 'and' and '&&'

cat = 'meow'
dog = false

answer = cat && dog
=> false

=>  false

answer = cat and dog
=> false

=> 'meow'

Similarly with 'or' and '||'

cat = false
dog = 'bark'

answer = cat || dog
 => 'bark'

=>  'bark'

answer = cat or dog
=> 'bark'

=> false

I generally follow this style guide

Beats to think to

Like to concentrate whilst listening to hypnotic deep house tracks?

I've found the playlist for you.

I use it to focus whilst programming, check it out

Timezone value from offset #rails

Some apis just return a timezone offset from UTC. For example Facebook

Need to convert it to a timezone name?

Rails Active Support to the rescue, you just need to do something like this:

utc_offset_in_hours = 10
time_zone = ActiveSupport::TimeZone[utc_offset_in_hours].name
=> "Brisbane"

Most recent git branches

Sometimes I work on a few branches at the same time.

Emergency bug fix branch here, new feature branch there, performance update branch here, update gem branch there, etc...

Within a big project we sometimes have almost 40 branches at any one time.

So, being human I forget the name of the branch that I was working on last week, and also would like to clean up old branches that I no longer need.

So the solution git for-each-ref

Include a sort and formatting that includes last commit date, and author name. This is the command:

git for-each-ref --count=30 --sort=-committerdate refs/heads/ --format='%(refname:short) %(committerdate) %(authorname)'

Home Entertainment

Recently I have been investigating what the cheapest/easiest setup could be for a home entertainment system would be.

I have an old Macbook laptop that doesn't have a working touchpad and keyboard - but everything else works, so am using that as a media server.

So, my favourite combination of Software/Hardware is:

  • Plex Server, easy to setup, works on all operating systems. You can add your own specific custom plugins, for example ABC iview in Australia, just look on GitHub.

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  • Chromecast - best $30 spent ever. Really simple device that works insanely well. Even without a media server, you can get some fantastic apps on your mobile - and cast from there.

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  • Plex mobile app ~$6, enables you to browse your Plex channels, and cast to your TV. Works on iPad, iPhone and Android.

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Now all I need is a decent live sports channel, and I'll be set.

Best Coffee Shops to work from in San Francisco

You'll see the Nodes, Rubies, the GitHubs, and get power points (mostly). Plus great Coffee.

Not too much VC raising - app idea BS either.

Ritual Coffee

1989 - 1996 : The Golden Years