Dockerfile parse error line 5: unknown instruction: -ESSENTIAL this is my dockerfile ; 

FROM ubuntu:16.04
MAINTAINER James Turnbull "james@example.com"
ENV REFRESHED_AT 2016-06-01
RUN apt-get update -yqq; apt-get -yqq install ruby ruby-dev build 
  -essential redis-tools

RUN gem install --no-rdoc --no-ri sinatra json redis
RUN mkdir -p /opt/webapp
EXPOSE 4567


CMD [ "/opt/webapp/bin/webapp" ]


and this is how i ran it : 


  docker build -t jamtur01/sinatra .


however i get this error in regard to  -essential 


  Dockerfile parse error line 5: unknown instruction: -ESSENTIAL


i am not clear what i have done wrong. is there an equivalent for -essential
I assume you have a copy-paste issue. The right package name is build-essential. And if you want to split a RUN statement over several lines, you will have to use backslash for line continuation.

All that leading to something along the lines of:

RUN apt-get update -yqq; apt-get -yqq install ruby ruby-dev \
          build-essential redis-tools


As a personal suggestion, when you have several commands to run, it is usually better to join them using &amp;&amp; rather than ; since you want the build to fail if either command is failing.

RUN apt-get update -yqq &amp;&amp; apt-get -yqq install ruby ruby-dev \
          build-essential redis-tools