diff --git a/test/e2e-common.sh b/test/e2e-common.sh
index 91237f716..8a8a8104d 100755
--- a/test/e2e-common.sh
+++ b/test/e2e-common.sh
@@ -43,7 +43,7 @@ export INGRESS_CLASS=${INGRESS_CLASS:-istio.ingress.networking.knative.dev}
 GENERATE_SERVING_YAML=0
 
 readonly OPERATOR_DIR="$(dirname "${BASH_SOURCE[0]}")/.."
-readonly KNATIVE_DIR=$(dirname ${OPERATOR_DIR})
+readonly KNATIVE_DIR=$(dirname "${OPERATOR_DIR}")
 release_yaml="$(mktemp)"
 release_eventing_yaml="$(mktemp)"
 
@@ -62,10 +62,10 @@ function add_trap() {
   local cmd=$1
   shift
   for trap_signal in $@; do
-    local current_trap="$(trap -p $trap_signal | cut -d\' -f2)"
+    local current_trap="$(trap -p "$trap_signal" | cut -d\' -f2)"
     local new_cmd="($cmd)"
     [[ -n "${current_trap}" ]] && new_cmd="${current_trap};${new_cmd}"
-    trap -- "${new_cmd}" $trap_signal
+    trap -- "${new_cmd}" "$trap_signal"
   done
 }
 
@@ -80,7 +80,7 @@ function test_setup_logging() {
   fi
 
   # Capture all logs.
-  kail > ${ARTIFACTS}/k8s.log-$(basename ${E2E_SCRIPT}).txt &
+  kail > "${ARTIFACTS}"/k8s.log-$(basename "${E2E_SCRIPT}").txt &
   local kail_pid=$!
   # Clean up kail so it doesn't interfere with job shutting down
   add_trap "kill $kail_pid || true" EXIT
@@ -102,30 +102,30 @@ function download_knative() {
   component_repo=$1
   component_name=$2
   # Go the directory to download the source code of knative
-  cd ${KNATIVE_DIR}
+  cd "${KNATIVE_DIR}" || exit
   # Download the source code of knative
   git clone "https://github.com/${component_repo}.git" "${component_name}"
-  cd "${component_name}"
+  cd "${component_name}" || exit
   local branch=$3
   if [ -n "${branch}" ] ; then
-    git fetch origin ${branch}:${branch}
-    git checkout ${branch}
+    git fetch origin "${branch}":"${branch}"
+    git checkout "${branch}"
   fi
-  cd ${OPERATOR_DIR}
+  cd "${OPERATOR_DIR}" || exit
 }
 
 # Install Istio.
 function install_istio() {
   echo ">> Installing Istio"
   curl -sL https://istio.io/downloadIstioctl | sh -
-  $HOME/.istioctl/bin/istioctl install -y
+  "$HOME"/.istioctl/bin/istioctl install -y
 }
 
 function create_namespace() {
   echo ">> Creating test namespaces for knative serving and eventing"
   # All the custom resources and Knative Serving resources are created under this TEST_NAMESPACE.
-  kubectl get ns ${TEST_NAMESPACE} || kubectl create namespace ${TEST_NAMESPACE}
-  kubectl get ns ${TEST_EVENTING_NAMESPACE} || kubectl create namespace ${TEST_EVENTING_NAMESPACE}
+  kubectl get ns "${TEST_NAMESPACE}" || kubectl create namespace "${TEST_NAMESPACE}"
+  kubectl get ns "${TEST_EVENTING_NAMESPACE}" || kubectl create namespace "${TEST_EVENTING_NAMESPACE}"
 }
 
 function download_latest_release() {