diff --git a/tests/4_container_images.sh b/tests/4_container_images.sh
index 3c7dec3..b319a5f 100644
--- a/tests/4_container_images.sh
+++ b/tests/4_container_images.sh
@@ -52,13 +52,13 @@ fi
 check_4_6="4.6  - Add HEALTHCHECK instruction to the container image"
 fail=0
 for img in $images; do
-  docker inspect --format='{{.Config.Healthcheck}}' $img 2>/dev/null | grep -e "<nil>" >/dev/null 2>&1
+  docker inspect --format='{{.Config.Healthcheck}}' "$img" 2>/dev/null | grep -e "<nil>" >/dev/null 2>&1
   if [ $? -eq 0 ]; then
     if [ $fail -eq 0 ]; then
       fail=1
       warn "$check_4_6"
     fi
-    imgName=`docker inspect --format='{{.RepoTags}}' $img 2>/dev/null`
+    imgName=$(docker inspect --format='{{.RepoTags}}' "$img" 2>/dev/null)
     warn "     * No Healthcheck found : $imgName"
   fi
 done
@@ -70,13 +70,13 @@ fi
 check_4_7="4.7  - Do not use update instructions alone in the Dockerfile"
 fail=0
 for img in $images; do
-  docker history $img 2>/dev/null | grep -e "update" >/dev/null 2>&1
+  docker history "$img" 2>/dev/null | grep -e "update" >/dev/null 2>&1
   if [ $? -eq 0 ]; then
     if [ $fail -eq 0 ]; then
       fail=1
       info "$check_4_7"
     fi
-    imgName=`docker inspect --format='{{.RepoTags}}' $img 2>/dev/null`
+    imgName=$(docker inspect --format='{{.RepoTags}}' "$img" 2>/dev/null)
     info "     * Update instruction found in history of $imgName"
   fi
 done
@@ -88,13 +88,13 @@ fi
 check_4_9="4.9  - Use COPY instead of ADD in Dockerfile"
 fail=0
 for img in $images; do
-  docker history $img 2> /dev/null | grep 'ADD' >/dev/null 2>&1
+  docker history "$img" 2> /dev/null | grep 'ADD' >/dev/null 2>&1
   if [ $? -eq 0 ]; then
     if [ $fail -eq 0 ]; then
       fail=1
       info "$check_4_9"
     fi
-    imgName=`docker inspect --format='{{.RepoTags}}' $img 2>/dev/null`
+    imgName=$(docker inspect --format='{{.RepoTags}}' "$img" 2>/dev/null)
     info "     * Found ADD in docker history of $imgName"
   fi
 done
diff --git a/tests/5_container_runtime.sh b/tests/5_container_runtime.sh
index dd984e9..6ff1557 100644
--- a/tests/5_container_runtime.sh
+++ b/tests/5_container_runtime.sh
@@ -591,7 +591,7 @@ else
 
   fail=0
   for c in $containers; do
-    pidslimit=`docker inspect --format '{{.HostConfig.PidsLimit }}' "$c"`
+    pidslimit=$(docker inspect --format '{{.HostConfig.PidsLimit }}' "$c")
 
     if [ $pidslimit -le 0 ]; then
       # If it's the first container, fail the test
@@ -613,12 +613,12 @@ else
   check_5_29="5.29 - Do not use Docker's default bridge docker0"
 
   fail=0
-  networks=`docker network ls -q 2>/dev/null`
+  networks=$(docker network ls -q 2>/dev/null)
   for net in $networks; do
     docker network inspect --format '{{ .Options }}' "$net" 2>/dev/null | grep "com.docker.network.bridge.name:docker0" >/dev/null 2>&1
 
     if [ $? -eq 0 ]; then
-      docker0Containers=`docker network inspect --format='{{ range $k, $v := .Containers }} {{ $k }} {{ end }}' "$net" 2>/dev/null`
+      docker0Containers=$(docker network inspect --format='{{ range $k, $v := .Containers }} {{ $k }} {{ end }}' "$net" 2>/dev/null)
       if [ -n "$docker0Containers" ]; then
         if [ $fail -eq 0 ]; then
           warn "$check_5_29"