Move install code to external script

Dockerfile

@@ -1,24 +1,8 @@
 FROM centos
 MAINTAINER PromptWorks <team@promptworks.com>
 
-RUN export RUBY_INSTALL_VERSION=0.4.0 && \
-    export RUBY_VERSION=2.0.0-p451 && \
-    cd /tmp && \
-    yum list installed | cut -f 1 -d " " | uniq | sort > /tmp/pre && \
-    yum install git -y && \
-    wget -O ruby-install-$RUBY_INSTALL_VERSION.tar.gz \
-      https://github.com/postmodern/ruby-install/archive/v$RUBY_INSTALL_VERSION.tar.gz && \
-    tar -xzf ruby-install-$RUBY_INSTALL_VERSION.tar.gz && \
-    cd ruby-install-$RUBY_INSTALL_VERSION && \
-    make install && \
-    ruby-install -i /usr/local ruby $RUBY_VERSION && \
-    make uninstall && \
-    yum list installed | cut -f 1 -d " " | uniq | sort > /tmp/post && \
-    diff /tmp/pre /tmp/post | grep "^>" | cut -f 2 -d ' ' | \
-      xargs echo yum erase -y && \
-    yum clean all && \
-    rm -rf /usr/local/src/ruby* && \
-    rm -rf /tmp/*
+ADD install_ruby.sh /tmp/
+RUN /tmp/install_ruby.sh
 
 RUN gem update --system --no-document
 RUN gem install bundler --no-ri --no-rdoc

install_ruby.sh

@@ -0,0 +1,23 @@
+#!/bin/bash -ex
+
+export RUBY_INSTALL_VERSION=0.4.0
+export RUBY_VERSION=2.0.0-p451
+
+cd /tmp
+
+yum list installed | cut -f 1 -d " " | uniq | sort > /tmp/pre
+yum install git -y
+
+wget -O ruby-install-$RUBY_INSTALL_VERSION.tar.gz \
+  https://github.com/postmodern/ruby-install/archive/v$RUBY_INSTALL_VERSION.tar.gz
+tar -xzf ruby-install-$RUBY_INSTALL_VERSION.tar.gz
+cd ruby-install-$RUBY_INSTALL_VERSION
+make install
+ruby-install -i /usr/local ruby $RUBY_VERSION
+
+make uninstall
+yum list installed | cut -f 1 -d " " | uniq | sort > /tmp/post
+diff /tmp/pre /tmp/post | grep "^>" | cut -f 2 -d ' ' | xargs echo yum erase -y
+yum clean all
+rm -rf /usr/local/src/ruby*
+rm -rf /tmp/*