Reduce layers count

Author: bamx23

Dockerfile

@@ -4,29 +4,28 @@ MAINTAINER Haris Amin <aminharis7@gmail.com>
 # Use baseimage-docker's init system.
 CMD ["/sbin/my_init"]
 
+ENV SWIFT_VERSION 2.2-SNAPSHOT-2015-12-01-b
+ENV SWIFT_PLATFORM ubuntu14.04
+
+# Install related packages
 RUN apt-get update && \
-    apt-get -y upgrade && \
     apt-get install -y build-essential wget clang libedit-dev python2.7 python2.7-dev libicu52 rsync && \
-    rm -rf /var/lib/apt/lists/*
-
-RUN wget -q -O - https://swift.org/keys/all-keys.asc | gpg --import -
-RUN gpg --keyserver hkp://pool.sks-keyservers.net --refresh-keys Swift
-
-# Download Swift Ubuntu 14.04 Snapshot, signature and verify
-RUN wget https://swift.org/builds/ubuntu1404/swift-2.2-SNAPSHOT-2015-12-01-b/swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04.tar.gz
-RUN wget https://swift.org/builds/ubuntu1404/swift-2.2-SNAPSHOT-2015-12-01-b/swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04.tar.gz.sig
-RUN gpg --verify swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04.tar.gz.sig
-
-RUN tar -xvzf swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04.tar.gz && cd swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04
-
-# Move extracted Swift Snapshot
-RUN rsync -a -v --ignore-existing swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04/usr/ /usr
-
-# Clean up
-RUN cd / && rm -rf swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04*
-
-# Clean up APT when done.
-RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+# Install Swift keys
+RUN wget -q -O - https://swift.org/keys/all-keys.asc | gpg --import - && \
+    gpg --keyserver hkp://pool.sks-keyservers.net --refresh-keys Swift
+
+# Install Swift Ubuntu 14.04 Snapshot
+RUN SWIFT_ARCHIVE_NAME=swift-$SWIFT_VERSION-$SWIFT_PLATFORM && \
+    SWIFT_URL=https://swift.org/builds/$(echo "$SWIFT_PLATFORM" | tr -d .)/swift-$SWIFT_VERSION/$SWIFT_ARCHIVE_NAME.tar.gz && \
+    wget $SWIFT_URL && \
+    wget $SWIFT_URL.sig && \
+    gpg --verify $SWIFT_ARCHIVE_NAME.tar.gz.sig && \
+    tar -xvzf $SWIFT_ARCHIVE_NAME.tar.gz && \
+    rsync -a -v --ignore-existing $SWIFT_ARCHIVE_NAME/usr/ /usr && \
+    rm -rf $SWIFT_ARCHIVE_NAME* /tmp/* /var/tmp/*
 
 # Set Swift Path
 ENV PATH /usr/bin:$PATH