From c8ff2de3b3d448d2055b6aaa75edad9afb9738c0 Mon Sep 17 00:00:00 2001
From: Matthias Radestock <matthias.radestock@gmail.com>
Date: Thu, 31 Dec 2015 12:51:16 +0000
Subject: [PATCH] properly deal with unavailable docker server api version

Fixes #1845.
---
 weave | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/weave b/weave
index 1e496569..5d88edc6 100755
--- a/weave
+++ b/weave
@@ -165,7 +165,7 @@ check_docker_server_api_version() {
     # Cope with various versions of `docker version` output format
     if ! DOCKER_API_VERSION=$(docker version -f '{{.Server.APIVersion}}' 2> /dev/null ) ; then
         if ! DOCKER_API_VERSION=$(docker version -f '{{.Server.ApiVersion}}' 2> /dev/null ) ; then
-            if ! DOCKER_API_VERSION=$(docker version | sed -n -e 's|^Server API version: *\([0-9][0-9]*\.[0-9][0-9]\).*|\1|p') ; then
+            if ! DOCKER_API_VERSION=$(docker version | sed -n -e 's|^Server API version: *\([0-9][0-9]*\.[0-9][0-9]\).*|\1|p') || [ -z "$DOCKER_API_VERSION" ] ; then
                 echo "ERROR: Unable to determine docker version" >&2
                 exit 1
             fi