[script] make property_utils.sh run on OSX + improve "if grep"

Now works on OSX: inline is required since in OSX providing '' as variable does not work.
More reliable OS independent version of this script.
Fixed incorrect backslash count in REGEX variable
Applied recommendations for "if grep" http://mywiki.wooledge.org/BashPitfalls#if_.5Bgrep_foo_myfile.5D

scripts/property_utils.sh

@@ -8,12 +8,6 @@
 
 set -euo pipefail
 
-if [[ "$OSTYPE" == "darwin"* ]]; then
-  SED_DISABLE_BACKUP=" ''"
-else
-  SED_DISABLE_BACKUP=""
-fi
-
 function cnt_lines() {
   FILE=$1
   cat $1 | wc -l
@@ -36,19 +30,27 @@ function set_property() {
   VALUE=$2
   FILE=$3
 
-  REGEXP="${1//\./\\\.}\s*="
-  if [ $(grep $REGEXP $FILE | wc -l) -eq 0 ]; then
-    write_prop $1 $2 $3
-  else
-    # delete line of specified property
+  REGEXP="${PROPERTY//\./\\.}\\s*="
+
+  if grep -q "$REGEXP" "$FILE"; then
+     # delete line of specified property
     LINE_COUNT=$(cnt_lines $FILE)
-    sed -i $SED_DISABLE_BACKUP "/${REGEXP}/d" $FILE
+
+    if [[ "$OSTYPE" == "darwin"* ]]; then
+      sed -i '' /${REGEXP}/d "$FILE"
+    else
+      sed -i /${REGEXP}/d "$FILE"
+    fi
 
     # add property if at least one line deleted
     NEW_LINE_COUNT=$(cnt_lines $FILE)
-    if [ $LINE_COUNT -gt $NEW_LINE_COUNT ]; then
+
+    if [[ $LINE_COUNT -gt $NEW_LINE_COUNT ]]; then
       write_prop $1 $2 $3
     fi
+
+  else
+    write_prop $1 $2 $3
   fi
 }