docker build ./sample-app

gistfile1.txt

Sending build context to Docker daemon 4.608 kB
Sending build context to Docker daemon 
Step 0 : FROM gurpartap/ruby-build:2.1.2
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Step 1 : RUN mkdir /app
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Step 2 : WORKDIR /app
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Step 3 : ADD Gemfile /app/Gemfile
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gistfile2.txt

Step 4 : RUN bundle install
 ---> Running in deca73d0c682
Don't run Bundler as root. Bundler can ask for sudo if it is needed, and
installing your bundle as root will break this application for all non-root
users on this machine.
Fetching gem metadata from https://rubygems.org/...........
Resolving dependencies...
Installing rake 10.3.2
Using bundler 1.7.2
Installing daemons 1.1.9
Installing eventmachine 1.0.3
Installing rack 1.5.2
Installing rack-protection 1.5.3
Installing tilt 1.4.1
Installing sinatra 1.4.5
Installing thin 1.6.2
Your bundle is complete!
Use `bundle show [gemname]` to see where a bundled gem is installed.
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gistfile3.txt

Step 5 : ADD . /app
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Step 6 : EXPOSE 3000
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Step 7 : CMD bundle exec thin start
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Successfully built b07106671777