diff --git a/helper/check-for-mysql b/helper/check-for-mysql
index c2a1970e..5500c082 100755
--- a/helper/check-for-mysql
+++ b/helper/check-for-mysql
@@ -8,7 +8,7 @@ else
   CONF="/etc/mysql/my.cnf"
 fi
 
-if [ $COUNT -le 0 ] ; then
+if [ "$COUNT" -le 0 ] ; then
   echo "Usage: $0 <number_of_seconds> [<mysqlid>]" >&2
   exit 1
 fi
@@ -45,8 +45,8 @@ mysqld_status () {
     ps_alive=1
   fi
 
-  if [ "$1" = "check_alive" -a $ping_alive = 1 ] ||
-     [ "$1" = "check_dead"  -a $ping_alive = 0 -a $ps_alive = 0 ]; then
+  if { [ "$1" = "check_alive" ] && [ "$ping_alive" = 1 ]; } ||
+      { [ "$1" = "check_dead" ] && [ "$ping_alive" = 0 ] && [ "$ps_alive" = 0 ]; }; then
     return 0
   fi
 
@@ -54,7 +54,7 @@ mysqld_status () {
 }
 
 printf "Checking MySQL service status (for a maximum of %s seconds): " "$COUNT"
-for _ in $(seq 1 $COUNT) ; do
+for _ in $(seq 1 "$COUNT") ; do
   if mysqld_status check_alive warn; then
     printf "available.\n"
     exit 0
diff --git a/scripts/services b/scripts/services
index 38faf6e3..042b2e58 100755
--- a/scripts/services
+++ b/scripts/services
@@ -193,6 +193,7 @@ find_instance() {
   local target
 
   # get rid of "./" and "//"
+  # shellcheck disable=SC2001
   service_file=$(echo "$1" | sed -e 's_\./_/_g ; s_//_/_g')
 
   for instance in "${INSTANCES[@]}"; do
@@ -228,7 +229,9 @@ find_changed_instance_services() {
   local target_file
 
   # get rid of "./" and "//"
+  # shellcheck disable=SC2001
   file=$(echo "$1"| sed -e 's_\./_/_g ; s_//_/_g')
+  # shellcheck disable=SC2001
   dir=$(echo "$2"| sed -e 's_\./_/_g ; s_//_/_g')
 
   for instance in "${INSTANCES[@]}"; do
diff --git a/t/fixtures/apply_instances/etc/kamailio/lb/ngcpcfg.services b/t/fixtures/apply_instances/etc/kamailio/lb/ngcpcfg.services
index 99a2369a..7fd44e49 100755
--- a/t/fixtures/apply_instances/etc/kamailio/lb/ngcpcfg.services
+++ b/t/fixtures/apply_instances/etc/kamailio/lb/ngcpcfg.services
@@ -1,3 +1,3 @@
 #!/bin/sh
 echo "INSTANCE_NAME:${INSTANCE_NAME:-}" > \
-  ${OUTPUT_DIRECTORY:-/tmp}/ngcpcfg.service${INSTANCE_NAME:-}
+  "${OUTPUT_DIRECTORY:-/tmp}/ngcpcfg.service${INSTANCE_NAME:-}"
diff --git a/t/fixtures/build_instances/etc/kamailio/lb/ngcpcfg.services b/t/fixtures/build_instances/etc/kamailio/lb/ngcpcfg.services
index 99a2369a..7fd44e49 100755
--- a/t/fixtures/build_instances/etc/kamailio/lb/ngcpcfg.services
+++ b/t/fixtures/build_instances/etc/kamailio/lb/ngcpcfg.services
@@ -1,3 +1,3 @@
 #!/bin/sh
 echo "INSTANCE_NAME:${INSTANCE_NAME:-}" > \
-  ${OUTPUT_DIRECTORY:-/tmp}/ngcpcfg.service${INSTANCE_NAME:-}
+  "${OUTPUT_DIRECTORY:-/tmp}/ngcpcfg.service${INSTANCE_NAME:-}"