diff --git a/Library/Homebrew/cmd/--version.sh b/Library/Homebrew/cmd/--version.sh
index c1d92a7a0d..bcd2d21264 100644
--- a/Library/Homebrew/cmd/--version.sh
+++ b/Library/Homebrew/cmd/--version.sh
@@ -2,30 +2,32 @@
 #:
 #:  Print the version numbers of Homebrew, Homebrew/homebrew-core and Homebrew/homebrew-cask (if tapped) to standard output.
 
+# HOMEBREW_CORE_REPOSITORY, HOMEBREW_CASK_REPOSITORY, HOMEBREW_VERSION are set by brew.sh
+# shellcheck disable=SC2154
 version_string() {
   local repo="$1"
-  if ! [ -d "$repo" ]; then
+  if ! [ -d "${repo}" ]; then
     echo "N/A"
     return
   fi
 
   local pretty_revision
-  pretty_revision="$(git -C "$repo" rev-parse --short --verify --quiet HEAD)"
-  if [ -z "$pretty_revision" ]; then
+  pretty_revision="$(git -C "${repo}" rev-parse --short --verify --quiet HEAD)"
+  if [ -z "${pretty_revision}" ]; then
     echo "(no Git repository)"
     return
   fi
 
   local git_last_commit_date
-  git_last_commit_date=$(git -C "$repo" show -s --format='%cd' --date=short HEAD)
+  git_last_commit_date=$(git -C "${repo}" show -s --format='%cd' --date=short HEAD)
   echo "(git revision ${pretty_revision}; last commit ${git_last_commit_date})"
 }
 
 homebrew-version() {
-  echo "Homebrew $HOMEBREW_VERSION"
-  echo "Homebrew/homebrew-core $(version_string "$HOMEBREW_CORE_REPOSITORY")"
+  echo "Homebrew ${HOMEBREW_VERSION}"
+  echo "Homebrew/homebrew-core $(version_string "${HOMEBREW_CORE_REPOSITORY}")"
 
-  if [ -d "$HOMEBREW_CASK_REPOSITORY" ]; then
-    echo "Homebrew/homebrew-cask $(version_string "$HOMEBREW_CASK_REPOSITORY")"
+  if [ -d "${HOMEBREW_CASK_REPOSITORY}" ]; then
+    echo "Homebrew/homebrew-cask $(version_string "${HOMEBREW_CASK_REPOSITORY}")"
   fi
 }