diff --git a/shadowsocksR b/shadowsocksR
index bc2e6d2..914b66a 100644
--- a/shadowsocksR
+++ b/shadowsocksR
@@ -24,8 +24,8 @@ fi
 RETVAL=0
 
 check_running(){
-    PID=`ps -ef | grep -v grep | grep -i "${BIN}" | awk '{print $2}'`
-    if [ ! -z "$PID" ]; then
+    PID=$(ps -ef | grep -v grep | grep -i "${BIN}" | awk '{print $2}')
+    if [ -n "$PID" ]; then
         return 0
     else
         return 1
diff --git a/shadowsocksR-debian b/shadowsocksR-debian
index ecfcff3..a109007 100644
--- a/shadowsocksR-debian
+++ b/shadowsocksR-debian
@@ -22,8 +22,8 @@ fi
 RETVAL=0
 
 check_running(){
-    PID=`ps -ef | grep -v grep | grep -i "${BIN}" | awk '{print $2}'`
-    if [ ! -z $PID ]; then
+    PID=$(ps -ef | grep -v grep | grep -i "${BIN}" | awk '{print $2}')
+    if [ -n "$PID" ]; then
         return 0
     else
         return 1