fix: test -s /tmp/duplicates.txt inside if

containers/jug/dev.Dockerfile

@@ -211,12 +211,14 @@ set -e
 make --jobs ${jobs} --keep-going --directory /opt/spack-environment \
   SPACK_ENV=${SPACK_ENV} SPACK_INSTALL_FLAGS="--use-buildcache only"
 spack gc --yes-to-all
-spack find --long --no-groups
 spack find --long --no-groups \
 | sed -e '1,/Installed packages/d;s/\([^@]*\).*/\1/g' \
 | uniq -D -f1 | grep -v -w -e "\(epic\|py-pip\|py-cython\)" \
 | tee /tmp/duplicates.txt
-test -s /tmp/duplicates.txt && ( cat /tmp/duplicates.txt | while read hash spec ; do spack spec --long /${hash} ; done ) && exit 1
+if [ -s /tmp/duplicates.txt ] ; then
+  cat /tmp/duplicates.txt | while read hash spec ; do spack spec --long /${hash} ; done
+  exit 1
+fi
 EOF
 
 ## Create views at /opt/local and /opt/detector