Adding improved error message when multiple assembly jars are present.

This can happen easily if building different hadoop versions.

spark-class

@@ -95,10 +95,17 @@ export JAVA_OPTS
 
 if [ ! -f "$FWDIR/RELEASE" ]; then
   # Exit if the user hasn't compiled Spark
-  ls "$FWDIR"/assembly/target/scala-$SCALA_VERSION/spark-assembly*hadoop*.jar >& /dev/null
-  if [[ $? != 0 ]]; then
-    echo "Failed to find Spark assembly in $FWDIR/assembly/target" >&2
-    echo "You need to build Spark with sbt/sbt assembly before running this program" >&2
+  num_jars=$(ls "$FWDIR"/assembly/target/scala-$SCALA_VERSION/ | grep "spark-assembly.*hadoop.*.jar" | wc -l)
+  jars_list=$(ls "$FWDIR"/assembly/target/scala-$SCALA_VERSION/ | grep "spark-assembly.*hadoop.*.jar")
+  if [ "$num_jars" -eq "0" ]; then
+    echo "Failed to find Spark assembly in $FWDIR/assembly/target/scala-$SCALA_VERSION/" >&2
+    echo "You need to build Spark with 'sbt/sbt assembly' before running this program." >&2
+    exit 1
+  fi
+  if [ "$num_jars" -gt "1" ]; then
+    echo "Found multiple Spark assembly jars in $FWDIR/assembly/target/scala-$SCALA_VERSION:" >&2
+    echo "$jars_list"
+    echo "Please remove all but one jar."
     exit 1
   fi
 fi