release.sh in killbill-paypal-express-1.6.5 vs release.sh in killbill-paypal-express-1.6.6

@@ -1,6 +1,19 @@
 set -e
 
+if [ "GNU" != "$(tar --help | grep GNU | head -1 | awk '{print $1}')" ]; then
+  echo "Unable to release: make sure to use GNU tar"
+  exit 1
+fi
+
+if $(ruby -e'require "java"'); then
+  # Good
+  echo "Detected JRuby"
+else
+  echo "Unable to release: make sure to use JRuby"
+  exit 1
+fi
+
 VERSION=`grep -E '<version>([0-9]+\.[0-9]+\.[0-9]+)</version>' pom.xml | sed 's/[\t \n]*<version>\(.*\)<\/version>[\t \n]*/\1/'`
 if [ "$VERSION" != "$(cat $PWD/VERSION)" ]; then
   echo "Unable to release: make sure the versions in pom.xml and VERSION match"
   exit 1
 fi