move terraform version to a docker build arg

This also opens things up to build images for multiple terraform versions.

Dockerfile

@@ -25,8 +25,8 @@ RUN apk -U add \
     openssh-client && \
     rm -rf /var/cache/apk/*
 
-ENV TERRAFORM_VERSION 0.12.4
+ARG terraform_version
-RUN wget -q https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip -O terraform.zip && \
+RUN wget -q https://releases.hashicorp.com/terraform/${terraform_version}/terraform_${terraform_version}_linux_amd64.zip -O terraform.zip && \
   unzip terraform.zip -d /bin && \
   rm -f terraform.zip
 

README.md

@@ -21,7 +21,9 @@ go build
 Build the docker image with the following commands:
 
 ```
-docker build --rm=true -t jmccann/drone-terraform .
+docker build --rm=true \
+  -t jmccann/drone-terraform \
+  --build-arg terraform_version=0.12.0 .
 ```
 
 ## Usage

build-docker.sh

@@ -13,7 +13,7 @@ major=$(echo $tag | awk -F. '{print $1}')
 minor=$(echo $tag | awk -F. '{print $2}')
 # patch=$(echo $tag | awk -F. '{print $3}')
 
-tf_ver=$(grep TERRAFORM_VERSION Dockerfile | head -n 1 | awk '{print $3}')
+tf_ver="0.12.4"
 
 echo "Confirm building images for:"
 echo "  MAJOR: ${major}"
@@ -28,7 +28,7 @@ if [[ "$ans" != "Y" && "$ans" != "y" ]]; then
 fi
 
 set -x
-docker build -t jmccann/drone-terraform:latest .
+docker build -t jmccann/drone-terraform:latest --build-arg terraform_version=${tf_ver} .
 
 docker tag jmccann/drone-terraform:latest jmccann/drone-terraform:${major}
 docker tag jmccann/drone-terraform:latest jmccann/drone-terraform:${major}.${minor}