fix build to update the git submodules.

cmake/build.sh

@@ -1,4 +1,29 @@
+# Get the location of this script, it is assumed you already cloned "main" and you are running the
+# script from that repo.  It will then put everything else in a ROS workspace at "../catkin_ws"
+SCRIPT=$(readlink -f "$0")
+SCRIPTPATH=$(dirname "$SCRIPT")
+pushd $SCRIPTPATH
+
+# update the rpclib git submodule
+pushd ..
+git submodule update --init --recursive 
+popd
+
+if [ -f "CMakeCache.txt" ]; then
 rm CMakeCache.txt 
+fi
+
+if [ -f "CMakeFiles" ]; then
 rm -rf CMakeFiles
-cmake -D CMAKE_BUILD_TYPE=Debug -D CMAKE_C_COMPILER=gcc-6 -D CMAKE_CXX_COMPILER=g++-6 CMakeLists.txt
+fi
+
+GCCARGS="-D CMAKE_BUILD_TYPE=Debug"
+
+GCCVERSION=$(gcc -v 2>&1 | sed -n "/^gcc version/p" | sed -e "s/^gcc version \([0-9]\)/\1/g" | cut -d"." -f1)
+if [ $GCCVERSION -lt 7 ]; then
+  GCCARGS="$GCCARGS -D CMAKE_C_COMPILER=gcc-6 -D CMAKE_CXX_COMPILER=g++-6"
+fi
+
+cmake $GCCARGS CMakeLists.txt
+
 make

docs/linux_build.md

@@ -8,6 +8,7 @@ If you don't have cmake version 3.* (for example, that is not the default on Ubu
 ````
 sudo add-apt-repository ppa:george-edison55/cmake-3.x -y
 sudo apt-get update
+sudo apt-get install cmake
 ````
 
 Then get the right version of Eigen, see [Install Eigen](install_eigen.md).