[SPARK-4504][Examples] fix run-example failure if multiple assembly jars exist

Fix run-example script to fail fast with useful error message if multiple
example assembly JARs are present.

Author: Venkata Ramana Gollamudi <ramana.gollamudi@huawei.com>

Closes #3377 from gvramana/run-example_fails and squashes the following commits:

fa7f481 [Venkata Ramana Gollamudi] Fixed review comments, avoiding ls output scanning.
6aa1ab7 [Venkata Ramana Gollamudi] Fix run-examples script error during multiple jars

1 files changed, 15 insertions, 12 deletions

diff --git a/bin/compute-classpath.sh b/bin/compute-classpath.sh
index 8f3b396ffd..9e8d0b7851 100755
--- a/bin/compute-classpath.sh
+++ b/bin/compute-classpath.sh
@@ -72,22 +72,25 @@ else
   assembly_folder="$ASSEMBLY_DIR"
 fi
 
-num_jars="$(ls "$assembly_folder" | grep "spark-assembly.*hadoop.*\.jar$" | wc -l)"
-if [ "$num_jars" -eq "0" ]; then
-  echo "Failed to find Spark assembly in $assembly_folder"
-  echo "You need to build Spark before running this program."
-  exit 1
-fi
+num_jars=0
+
+for f in ${assembly_folder}/spark-assembly*hadoop*.jar; do
+  if [[ ! -e "$f" ]]; then
+    echo "Failed to find Spark assembly in $assembly_folder" 1>&2
+    echo "You need to build Spark before running this program." 1>&2
+    exit 1
+  fi
+  ASSEMBLY_JAR="$f"
+  num_jars=$((num_jars+1))
+done
+
 if [ "$num_jars" -gt "1" ]; then
-  jars_list=$(ls "$assembly_folder" | grep "spark-assembly.*hadoop.*.jar$")
-  echo "Found multiple Spark assembly jars in $assembly_folder:"
-  echo "$jars_list"
-  echo "Please remove all but one jar."
+  echo "Found multiple Spark assembly jars in $assembly_folder:" 1>&2
+  ls ${assembly_folder}/spark-assembly*hadoop*.jar 1>&2
+  echo "Please remove all but one jar." 1>&2
   exit 1
 fi
 
-ASSEMBLY_JAR="$(ls "$assembly_folder"/spark-assembly*hadoop*.jar 2>/dev/null)"
-
 # Verify that versions of java used to build the jars and run Spark are compatible
 jar_error_check=$("$JAR_CMD" -tf "$ASSEMBLY_JAR" nonexistent/class/path 2>&1)
 if [[ "$jar_error_check" =~ "invalid CEN header" ]]; then