add post_push tagging for semantic versioning

hooks/post_push

@@ -0,0 +1,41 @@
+#!/bin/bash
+# hooks/post_push
+
+# https://docs.docker.com/docker-cloud/builds/advanced/
+# https://semver.org/
+
+function add_tag() {
+    echo "Adding tag ${1}"
+    docker tag $IMAGE_NAME $DOCKER_REPO:$1
+    docker push $DOCKER_REPO:$1
+}
+
+TAG=`git describe --tag --match "v*"`
+
+MAJOR=`echo ${TAG} | awk -F'-' '{print $1}' | awk -F'.' '{print $1}' | sed 's/v//'`
+MINOR=`echo ${TAG} | awk -F'-' '{print $1}' | awk -F'.' '{print $2}' | sed 's/v//'`
+PATCH=`echo ${TAG} | awk -F'-' '{print $1}' | awk -F'.' '{print $3}' | sed 's/v//'`
+PRLS=`echo ${TAG} | awk -F'-' '{print $2}'`
+
+num='^[0-9]+$'
+pre='^[0-9A-Za-z\.]+$'
+
+echo "Current Build: ${TAG}"
+
+if [ ! -z $MAJOR ] && [[ $MAJOR =~ $num ]]; then
+    add_tag ${MAJOR}
+
+    if [ ! -z $MINOR ] && [[ $MINOR =~ $num ]]; then
+        add_tag ${MAJOR}.${MINOR}
+
+        if [ ! -z $PATCH ] && [[ $PATCH =~ $num ]]; then
+            add_tag ${MAJOR}.${MINOR}.${PATCH}
+
+            if [ ! -z $PRLS ] && [[ ! $PRLS =~ $num ]] && [[ $PRLS =~ $pre ]]; then
+                add_tag ${MAJOR}.${MINOR}.${PATCH}-${PRLS}
+            fi
+        fi
+    fi
+fi
+
+exit $?