diff --git a/Library/Homebrew/utils/analytics.sh b/Library/Homebrew/utils/analytics.sh
index 456e2d5490..fe26e0bbed 100644
--- a/Library/Homebrew/utils/analytics.sh
+++ b/Library/Homebrew/utils/analytics.sh
@@ -1,43 +1,46 @@
 # Migrate analytics UUID to its new home in Homebrew repo's git config and
 # remove the legacy UUID file if detected.
+# HOMEBREW_LINUX, HOMEBREW_REPOSITORY is set by bin/brew
+# HOMEBREW_NO_ANALYTICS is from the user environment.
+# shellcheck disable=SC2154
 migrate-legacy-uuid-file() {
   local legacy_uuid_file analytics_uuid
 
-  legacy_uuid_file="$HOME/.homebrew_analytics_user_uuid"
+  legacy_uuid_file="${HOME}/.homebrew_analytics_user_uuid"
 
-  if [[ -f "$legacy_uuid_file" ]]
+  if [[ -f "${legacy_uuid_file}" ]]
   then
-    analytics_uuid="$(<"$legacy_uuid_file")"
-    if [[ -n "$analytics_uuid" ]]
+    analytics_uuid="$(<"${legacy_uuid_file}")"
+    if [[ -n "${analytics_uuid}" ]]
     then
-      git config --file="$HOMEBREW_REPOSITORY/.git/config" --replace-all homebrew.analyticsuuid "$analytics_uuid" 2>/dev/null
+      git config --file="${HOMEBREW_REPOSITORY}/.git/config" --replace-all homebrew.analyticsuuid "${analytics_uuid}" 2>/dev/null
     fi
-    rm -f "$legacy_uuid_file"
+    rm -f "${legacy_uuid_file}"
   fi
 }
 
 setup-analytics() {
-  local git_config_file="$HOMEBREW_REPOSITORY/.git/config"
+  local git_config_file="${HOMEBREW_REPOSITORY}/.git/config"
 
   migrate-legacy-uuid-file
 
-  if [[ -n "$HOMEBREW_NO_ANALYTICS" ]]
+  if [[ -n "${HOMEBREW_NO_ANALYTICS}" ]]
   then
     return
   fi
 
   local message_seen analytics_disabled
-  message_seen="$(git config --file="$git_config_file" --get homebrew.analyticsmessage 2>/dev/null)"
-  analytics_disabled="$(git config --file="$git_config_file" --get homebrew.analyticsdisabled 2>/dev/null)"
-  if [[ "$message_seen" != "true" || "$analytics_disabled" = "true" ]]
+  message_seen="$(git config --file="${git_config_file}" --get homebrew.analyticsmessage 2>/dev/null)"
+  analytics_disabled="$(git config --file="${git_config_file}" --get homebrew.analyticsdisabled 2>/dev/null)"
+  if [[ "${message_seen}" != "true" || "${analytics_disabled}" = "true" ]]
   then
     # Internal variable for brew's use, to differentiate from user-supplied setting
     export HOMEBREW_NO_ANALYTICS_THIS_RUN="1"
     return
   fi
 
-  HOMEBREW_ANALYTICS_USER_UUID="$(git config --file="$git_config_file" --get homebrew.analyticsuuid 2>/dev/null)"
-  if [[ -z "$HOMEBREW_ANALYTICS_USER_UUID" ]]
+  HOMEBREW_ANALYTICS_USER_UUID="$(git config --file="${git_config_file}" --get homebrew.analyticsuuid 2>/dev/null)"
+  if [[ -z "${HOMEBREW_ANALYTICS_USER_UUID}" ]]
   then
     if [[ -x /usr/bin/uuidgen ]]
     then
@@ -49,16 +52,16 @@ setup-analytics() {
       HOMEBREW_ANALYTICS_USER_UUID="$(uuidgen)"
     fi
 
-    if [[ -z "$HOMEBREW_ANALYTICS_USER_UUID" ]]
+    if [[ -z "${HOMEBREW_ANALYTICS_USER_UUID}" ]]
     then
       # Avoid sending bogus analytics if no UUID could be generated.
       export HOMEBREW_NO_ANALYTICS_THIS_RUN="1"
       return
     fi
-    git config --file="$git_config_file" --replace-all homebrew.analyticsuuid "$HOMEBREW_ANALYTICS_USER_UUID" 2>/dev/null
+    git config --file="${git_config_file}" --replace-all homebrew.analyticsuuid "${HOMEBREW_ANALYTICS_USER_UUID}" 2>/dev/null
   fi
 
-  if [[ -n "$HOMEBREW_LINUX" ]]
+  if [[ -n "${HOMEBREW_LINUX}" ]]
   then
     # For Homebrew on Linux's analytics.
     HOMEBREW_ANALYTICS_ID="UA-76492262-1"