diff --git a/Library/Homebrew/dev-cmd/rubocop.sh b/Library/Homebrew/dev-cmd/rubocop.sh
index 3351d2a245..9ef5e239ac 100644
--- a/Library/Homebrew/dev-cmd/rubocop.sh
+++ b/Library/Homebrew/dev-cmd/rubocop.sh
@@ -2,22 +2,27 @@
 #:
 #:  Installs, configures and runs Homebrew's `rubocop`.
 
+# HOMEBREW_LIBRARY is from the user environment.
+# HOMEBREW_RUBY_PATH is set by utils/ruby.sh
+# RUBY_DISABLE_OPTIONS is set by brew.sh
+# HOMEBREW_BREW_FILE is set by extend/ENV/super.rb
+# shellcheck disable=SC2154
 homebrew-rubocop() {
   # Don't need shellcheck to follow this `source`.
   # shellcheck disable=SC1090
-  source "$HOMEBREW_LIBRARY/Homebrew/utils/ruby.sh"
+  source "${HOMEBREW_LIBRARY}/Homebrew/utils/ruby.sh"
   setup-ruby-path
 
-  GEM_VERSION="$("$HOMEBREW_RUBY_PATH" "$RUBY_DISABLE_OPTIONS" -rrbconfig -e 'puts RbConfig::CONFIG["ruby_version"]')"
-  GEM_HOME="$HOMEBREW_LIBRARY/Homebrew/vendor/bundle/ruby/$GEM_VERSION"
+  GEM_VERSION="$("${HOMEBREW_RUBY_PATH}" "${RUBY_DISABLE_OPTIONS}" -rrbconfig -e 'puts RbConfig::CONFIG["ruby_version"]')"
+  GEM_HOME="${HOMEBREW_LIBRARY}/Homebrew/vendor/bundle/ruby/${GEM_VERSION}"
 
-  if ! [[ -f "$GEM_HOME/bin/rubocop" ]]; then
-    "$HOMEBREW_BREW_FILE" install-bundler-gems
+  if ! [[ -f "${GEM_HOME}/bin/rubocop" ]]; then
+    "${HOMEBREW_BREW_FILE}" install-bundler-gems
   fi
 
   export GEM_HOME
-  export PATH="$GEM_HOME/bin:$PATH"
+  export PATH="${GEM_HOME}/bin:${PATH}"
 
-  RUBOCOP="$HOMEBREW_LIBRARY/Homebrew/utils/rubocop.rb"
-  exec "$HOMEBREW_RUBY_PATH" "$RUBOCOP" "$@"
+  RUBOCOP="${HOMEBREW_LIBRARY}/Homebrew/utils/rubocop.rb"
+  exec "${HOMEBREW_RUBY_PATH}" "${RUBOCOP}" "$@"
 }