dockerfile: define PG_VERSION as an ENV variable

Dockerfile

@@ -1,10 +1,11 @@
 FROM sameersbn/ubuntu:14.04.20150120
 MAINTAINER sameer@damagehead.com
 
+ENV PG_VERSION 9.1
 RUN wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add - \
  && echo 'deb http://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main' > /etc/apt/sources.list.d/pgdg.list \
  && apt-get update \
- && apt-get install -y postgresql-9.1 postgresql-client-9.1 pwgen \
+ && apt-get install -y postgresql-${PG_VERSION} postgresql-client-${PG_VERSION} pwgen \
  && rm -rf /var/lib/postgresql \
  && rm -rf /var/lib/apt/lists/* # 20141001
 

start

@@ -1,7 +1,6 @@
 #!/bin/bash
 set -e
 
-PG_VERSION="9.1"
 PG_CONFDIR="/etc/postgresql/${PG_VERSION}/main"
 PG_BINDIR="/usr/lib/postgresql/${PG_VERSION}/bin"
 PG_DATADIR="/var/lib/postgresql/${PG_VERSION}/main"