log_merge: Use shelcheck to harden the script

Change-Id: I1b3a35b5f7ada2dbb0401a5d90a77a53979e1183
diff --git a/log_merge.sh b/log_merge.sh
index df52cfe..dee9cc2 100755
--- a/log_merge.sh
+++ b/log_merge.sh
@@ -7,7 +7,7 @@
 #
 # the output files will be called "Module-Testcase.merged"
 
-if [ "x$1" == "x" ]; then
+if [ "x$1" = "x" ]; then
 	echo "You have to specify the Test Suite prefix"
 	exit 2
 fi
@@ -15,16 +15,16 @@
 BASE_NAME="$1"
 LOG_FILES="$BASE_NAME*.log"
 
-TEST_CASES=`ls -1 $LOG_FILES | awk 'BEGIN { FS = "-" } { print $2 }' | sort | uniq`
+TEST_CASES=$(ls -1 $LOG_FILES | awk 'BEGIN { FS = "-" } { print $2 }' | sort | uniq)
 
 for t in $TEST_CASES; do
 	PREFIX="$BASE_NAME-$t"
 	OUTPUT="$BASE_NAME.$t.merged"
-	ttcn3_logmerge $PREFIX-*.log > $OUTPUT
+	ttcn3_logmerge $PREFIX-*.log > "$OUTPUT"
 	echo "Generated $OUTPUT"
 done
 
-if [ "$2" == "--rm" ]; then
+if [ "$2" = "--rm" ]; then
 	echo "Removing Input log files !!!"
-	rm $LOG_FILES
+	rm "$LOG_FILES"
 fi