[FLINK-27754][shell] Add stderr when singular flink-dist*.jar cannot …

…be resolved for config.sh.

README.md

@@ -75,7 +75,7 @@ Prerequisites for building Flink:
 ```
 git clone https://github.com/apache/flink.git
 cd flink
-mvn clean package -DskipTests # this will take up to 10 minutes
+./mvnw clean package -DskipTests # this will take up to 10 minutes
 ```
 
 Flink is now installed in `build-target`.

flink-dist/src/main/flink-bin/bin/config.sh

@@ -31,25 +31,35 @@ constructFlinkClassPath() {
         fi
     done < <(find "$FLINK_LIB_DIR" ! -type d -name '*.jar' -print0 | sort -z)
 
+    local FLINK_DIST_COUNT
+    FLINK_DIST_COUNT="$(echo "$FLINK_DIST" | wc -l)"
+
+    # If flink-dist*.jar cannot be resolved write error messages to stderr since stdout is stored
+    # as the classpath and exit function with empty classpath to force process failure
     if [[ "$FLINK_DIST" == "" ]]; then
-        # write error message to stderr since stdout is stored as the classpath
         (>&2 echo "[ERROR] Flink distribution jar not found in $FLINK_LIB_DIR.")
-
-        # exit function with empty classpath to force process failure
+        exit 1
+    elif [[ "$FLINK_DIST_COUNT" -gt 1 ]]; then
+        (>&2 echo "[ERROR] Multiple flink-dist*.jar found in $FLINK_LIB_DIR. Please resolve.")
         exit 1
     fi
 
     echo "$FLINK_CLASSPATH""$FLINK_DIST"
 }
 
 findFlinkDistJar() {
-    local FLINK_DIST="`find "$FLINK_LIB_DIR" -name 'flink-dist*.jar'`"
+    local FLINK_DIST
+    FLINK_DIST="$(find "$FLINK_LIB_DIR" -name 'flink-dist*.jar')"
+    local FLINK_DIST_COUNT
+    FLINK_DIST_COUNT="$(echo "$FLINK_DIST" | wc -l)"
 
+    # If flink-dist*.jar cannot be resolved write error messages to stderr since stdout is stored
+    # as the classpath and exit function with empty classpath to force process failure
     if [[ "$FLINK_DIST" == "" ]]; then
-        # write error message to stderr since stdout is stored as the classpath
         (>&2 echo "[ERROR] Flink distribution jar not found in $FLINK_LIB_DIR.")
-
-        # exit function with empty classpath to force process failure
+        exit 1
+    elif [[ "$FLINK_DIST_COUNT" -gt 1 ]]; then
+        (>&2 echo "[ERROR] Multiple flink-dist*.jar found in $FLINK_LIB_DIR. Please resolve.")
         exit 1
     fi