diff --git a/update.sh b/update.sh
index 1f53cfc44e..0cb0bef356 100755
--- a/update.sh
+++ b/update.sh
@@ -48,17 +48,17 @@ function update_node_version() {
     shift
   fi
 
-  fullVersion="$(curl -sSL --compressed "$baseuri" | grep '<a href="v'"$version." | sed -E 's!.*<a href="v([^"/]+)/?".*!\1!' | cut -d'.' -f2,3 | sort -n | tail -1)"
+  fullVersion="$(curl -sSL --compressed "${baseuri}" | grep '<a href="v'"${version}." | sed -E 's!.*<a href="v([^"/]+)/?".*!\1!' | cut -d'.' -f2,3 | sort -n | tail -1)"
   (
-    cp "$template" "$dockerfile"
+    cp "${template}" "${dockerfile}"
     local fromprefix=""
-    if [ "$arch" != "amd64" ] && [ "$variant" != "onbuild" ]; then
-      fromprefix="$arch\\/"
+    if [ "${arch}" != "amd64" ] && [ "${variant}" != "onbuild" ]; then
+      fromprefix="${arch}\\/"
     fi
 
-    sed -E -i.bak 's/^FROM (.*)/FROM '"$fromprefix"'\1/' "$dockerfile" && rm "$dockerfile".bak
-    sed -E -i.bak 's/^(ENV NODE_VERSION |FROM .*node:).*/\1'"$version.${fullVersion:-0}"'/' "$dockerfile" && rm "$dockerfile".bak
-    sed -E -i.bak 's/^(ENV YARN_VERSION ).*/\1'"$yarnVersion"'/' "$dockerfile" && rm "$dockerfile".bak
+    sed -Ei -e 's/^FROM (.*)/FROM '"${fromprefix}"'\1/' "${dockerfile}"
+    sed -Ei -e 's/^(ENV NODE_VERSION |FROM .*node:).*/\1'"${version}.${fullVersion:-0}"'/' "${dockerfile}"
+    sed -Ei -e 's/^(ENV YARN_VERSION ).*/\1'"${yarnVersion}"'/' "$dockerfile"
 
     # shellcheck disable=SC1004
     new_line=' \\\
@@ -67,18 +67,16 @@ function update_node_version() {
     # Add GPG keys
     for key_type in "node" "yarn"; do
       while read -r line; do
-        pattern="\"\\$\\{$(echo "$key_type" | tr '[:lower:]' '[:upper:]')_KEYS\\[@\\]\\}\""
-        sed -E -i.bak -e "s/([ \\t]*)($pattern)/\\1${line}${new_line}\\1\\2/" "$dockerfile" && rm "$dockerfile".bak
+        pattern="\"\\$\\{$(echo "${key_type}" | tr '[:lower:]' '[:upper:]')_KEYS\\[@\\]\\}\""
+        sed -Ei -e "s/([ \\t]*)(${pattern})/\\1${line}${new_line}\\1\\2/" "${dockerfile}"
       done <"keys/$key_type.keys"
-      sed -E -i.bak "/$pattern/d" "$dockerfile" && rm "$dockerfile".bak
+      sed -Ei -e "/${pattern}/d" "${dockerfile}"
     done
 
     if [ "${version/.*/}" -ge 10 ]; then
-      sed -E -i.bak 's/FROM (.*)alpine:3.4/FROM \1alpine:3.7/' "$dockerfile"
-      rm "$dockerfile.bak"
+      sed -Ei -e 's/FROM (.*)alpine:3.4/FROM \1alpine:3.7/' "${dockerfile}"
     elif [ "${version/.*/}" -ge 8 ] || [ "$arch" = "ppc64le" ] || [ "$arch" = "s390x" ] || [ "$arch" == "arm64" ] || [ "$arch" == "arm32v7" ]; then
-      sed -E -i.bak 's/FROM (.*)alpine:3.4/FROM \1alpine:3.6/' "$dockerfile"
-      rm "$dockerfile.bak"
+      sed -Ei -e 's/FROM (.*)alpine:3.4/FROM \1alpine:3.6/' "${dockerfile}"
     fi
   )
 }
@@ -94,8 +92,8 @@ function add_stage() {
   echo '
     - stage: Build
       env:
-        - NODE_VERSION: "'"$version"'"
-        - VARIANT: "'"$variant"'"' >>.travis.yml
+        - NODE_VERSION: "'"${version}"'"
+        - VARIANT: "'"${variant}"'"' >>.travis.yml
 }
 
 echo '#### DO NOT MODIFY. THIS FILE IS AUTOGENERATED ####
@@ -103,18 +101,18 @@ echo '#### DO NOT MODIFY. THIS FILE IS AUTOGENERATED ####
 
 for version in "${versions[@]}"; do
   # Skip "docs" and other non-docker directories
-  [ -f "$version/Dockerfile" ] || continue
+  [ -f "${version}/Dockerfile" ] || continue
 
   parentpath=$(dirname "$version")
   versionnum=$(basename "$version")
   baseuri=$(get_config "$parentpath" "baseuri")
   update=$(in_versions_to_update "$version")
 
-  add_stage "$baseuri" "$version" "default"
+  add_stage "${baseuri}" "${version}" "default"
 
-  if [ "$update" -eq 0 ]; then
+  if [ "${update}" -eq 0 ]; then
     info "Updating version $version..."
-    update_node_version "$baseuri" "$versionnum" "$parentpath/Dockerfile.template" "$version/Dockerfile" &
+    update_node_version "${baseuri}" "${versionnum}" "${parentpath}/Dockerfile.template" "${version}/Dockerfile" &
   fi
 
   # Get supported variants according the target architecture
@@ -123,11 +121,11 @@ for version in "${versions[@]}"; do
 
   for variant in "${variants[@]}"; do
     # Skip non-docker directories
-    [ -f "$version/$variant/Dockerfile" ] || continue
-    add_stage "$baseuri" "$version" "$variant"
+    [ -f "${version}/${variant}/Dockerfile" ] || continue
+    add_stage "${baseuri}" "${version}" "${variant}"
 
-    if [ "$update" -eq 0 ]; then
-      update_node_version "$baseuri" "$versionnum" "$parentpath/Dockerfile-$variant.template" "$version/$variant/Dockerfile" "$variant" &
+    if [ "${update}" -eq 0 ]; then
+      update_node_version "${baseuri}" "${versionnum}" "${parentpath}/Dockerfile-${variant}.template" "${version}/${variant}/Dockerfile" "${variant}" &
     fi
   done
 done