Update start

Author: eeholmes

start

@@ -8,7 +8,7 @@ set -euo pipefail
 # pop open GUIs
 export DISPLAY=":1.0"
 # source this file to get the variables defined in the rocker Dockerfile
-source ${REPO_DIR}/env.txt
+[ -f "${REPO_DIR}/env.txt" ] && source "${REPO_DIR}/env.txt"
 
 # The for loops will fail if they return null (no files). Set shell option nullglob
 shopt -s nullglob