Introduce docker version check into scope script, error on <1.5.0

scope

@@ -29,6 +29,34 @@ WEAVESCOPE_DOCKER_ARGS=${WEAVESCOPE_DOCKER_ARGS:-}
 COMMAND=$1
 shift 1
 
+# - The image embeds the weave script & Docker 1.3.1 client
+# - Docker versions prior to 1.5.0 do not support --pid=host
+MIN_DOCKER_VERSION=1.5.0
+
+check_docker_version() {
+    if ! DOCKER_VERSION=$(docker -v | sed -n -e 's|^Docker version \([0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\).*|\1|p') || [ -z "$DOCKER_VERSION" ] ; then
+        echo "ERROR: Unable to parse docker version" >&2
+        exit 1
+    fi
+
+    DOCKER_VERSION_MAJOR=$(echo "$DOCKER_VERSION" | cut -d. -f 1)
+    DOCKER_VERSION_MINOR=$(echo "$DOCKER_VERSION" | cut -d. -f 2)
+    DOCKER_VERSION_PATCH=$(echo "$DOCKER_VERSION" | cut -d. -f 3)
+
+    MIN_DOCKER_VERSION_MAJOR=$(echo "$MIN_DOCKER_VERSION" | cut -d. -f 1)
+    MIN_DOCKER_VERSION_MINOR=$(echo "$MIN_DOCKER_VERSION" | cut -d. -f 2)
+    MIN_DOCKER_VERSION_PATCH=$(echo "$MIN_DOCKER_VERSION" | cut -d. -f 3)
+
+    if [ \( "$DOCKER_VERSION_MAJOR" -lt "$MIN_DOCKER_VERSION_MAJOR" \) -o \
+        \( "$DOCKER_VERSION_MAJOR" -eq "$MIN_DOCKER_VERSION_MAJOR" -a \
+        \( "$DOCKER_VERSION_MINOR" -lt "$MIN_DOCKER_VERSION_MINOR" -o \
+        \( "$DOCKER_VERSION_MINOR" -eq "$MIN_DOCKER_VERSION_MINOR" -a \
+        \( "$DOCKER_VERSION_PATCH" -lt "$MIN_DOCKER_VERSION_PATCH" \) \) \) \) ] ; then
+        echo "ERROR: scope requires Docker version $MIN_DOCKER_VERSION or later; you are running $DOCKER_VERSION" >&2
+        exit 1
+    fi
+}
+
 # Check that a container named $1 with image $2 is not running
 check_not_running() {
     case $(docker inspect --format='{{.State.Running}} {{.Config.Image}}' $1 2>/dev/null) in
@@ -57,6 +85,8 @@ check_not_running() {
     esac
 }
 
+check_docker_version
+
 case "$COMMAND" in
 
     launch)