diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 5fbb120346..d7d6f8b2f2 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -315,6 +315,7 @@ then
 fi
 
 HOMEBREW_CORE_REPOSITORY="${HOMEBREW_LIBRARY}/Taps/homebrew/homebrew-core"
+HOMEBREW_CASK_REPOSITORY="${HOMEBREW_LIBRARY}/Taps/homebrew/homebrew-cask"
 
 case "$*" in
   --version|-v) source "${HOMEBREW_LIBRARY}/Homebrew/cmd/--version.sh"; homebrew-version; exit 0 ;;
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
 }
diff --git a/Library/Homebrew/cmd/casks.sh b/Library/Homebrew/cmd/casks.sh
index 4a8d866f45..aa3a75cf2b 100644
--- a/Library/Homebrew/cmd/casks.sh
+++ b/Library/Homebrew/cmd/casks.sh
@@ -3,7 +3,9 @@
 #:  List all locally installable casks including short names.
 #:
 
-source "$HOMEBREW_LIBRARY/Homebrew/items.sh"
+# HOMEBREW_LIBRARY is set in bin/brew
+# shellcheck disable=SC2154
+source "${HOMEBREW_LIBRARY}/Homebrew/items.sh"
 
 homebrew-casks() {
   homebrew-items 'Formula' 's|/Casks/|/|' '^homebrew/cask'
diff --git a/Library/Homebrew/cmd/shellenv.sh b/Library/Homebrew/cmd/shellenv.sh
index 39327d20fc..d7f2e73972 100644
--- a/Library/Homebrew/cmd/shellenv.sh
+++ b/Library/Homebrew/cmd/shellenv.sh
@@ -5,31 +5,34 @@
 #:  The variables `HOMEBREW_PREFIX`, `HOMEBREW_CELLAR` and `HOMEBREW_REPOSITORY` are also exported to avoid querying them multiple times.
 #:  Consider adding evaluation of this command's output to your dotfiles (e.g. `~/.profile`, `~/.bash_profile`, or `~/.zprofile`) with: `eval $(brew shellenv)`
 
+# HOMEBREW_CELLAR and HOMEBREW_PREFIX are set by extend/ENV/super.rb
+# HOMEBREW_REPOSITORY is set by bin/brew
+# shellcheck disable=SC2154
 homebrew-shellenv() {
-  case "$(/bin/ps -p $PPID -c -o comm=)" in
+  case "$(/bin/ps -p "${PPID}" -c -o comm=)" in
     fish|-fish)
-      echo "set -gx HOMEBREW_PREFIX \"$HOMEBREW_PREFIX\";"
-      echo "set -gx HOMEBREW_CELLAR \"$HOMEBREW_CELLAR\";"
-      echo "set -gx HOMEBREW_REPOSITORY \"$HOMEBREW_REPOSITORY\";"
-      echo "set -q PATH; or set PATH ''; set -gx PATH \"$HOMEBREW_PREFIX/bin\" \"$HOMEBREW_PREFIX/sbin\" \$PATH;"
-      echo "set -q MANPATH; or set MANPATH ''; set -gx MANPATH \"$HOMEBREW_PREFIX/share/man\" \$MANPATH;"
-      echo "set -q INFOPATH; or set INFOPATH ''; set -gx INFOPATH \"$HOMEBREW_PREFIX/share/info\" \$INFOPATH;"
+      echo "set -gx HOMEBREW_PREFIX \"${HOMEBREW_PREFIX}\";"
+      echo "set -gx HOMEBREW_CELLAR \"${HOMEBREW_CELLAR}\";"
+      echo "set -gx HOMEBREW_REPOSITORY \"${HOMEBREW_REPOSITORY}\";"
+      echo "set -q PATH; or set PATH ''; set -gx PATH \"${HOMEBREW_PREFIX}/bin\" \"${HOMEBREW_PREFIX}/sbin\" \$PATH;"
+      echo "set -q MANPATH; or set MANPATH ''; set -gx MANPATH \"${HOMEBREW_PREFIX}/share/man\" \$MANPATH;"
+      echo "set -q INFOPATH; or set INFOPATH ''; set -gx INFOPATH \"${HOMEBREW_PREFIX}/share/info\" \$INFOPATH;"
       ;;
     csh|-csh|tcsh|-tcsh)
-      echo "setenv HOMEBREW_PREFIX $HOMEBREW_PREFIX;"
-      echo "setenv HOMEBREW_CELLAR $HOMEBREW_CELLAR;"
-      echo "setenv HOMEBREW_REPOSITORY $HOMEBREW_REPOSITORY;"
-      echo "setenv PATH $HOMEBREW_PREFIX/bin:$HOMEBREW_PREFIX/sbin:\$PATH;"
-      echo "setenv MANPATH $HOMEBREW_PREFIX/share/man\`[ \${?MANPATH} == 1 ] && echo \":\${MANPATH}\"\`:;"
-      echo "setenv INFOPATH $HOMEBREW_PREFIX/share/info\`[ \${?INFOPATH} == 1 ] && echo \":\${INFOPATH}\"\`;"
+      echo "setenv HOMEBREW_PREFIX ${HOMEBREW_PREFIX};"
+      echo "setenv HOMEBREW_CELLAR ${HOMEBREW_CELLAR};"
+      echo "setenv HOMEBREW_REPOSITORY ${HOMEBREW_REPOSITORY};"
+      echo "setenv PATH ${HOMEBREW_PREFIX}/bin:${HOMEBREW_PREFIX}/sbin:\$PATH;"
+      echo "setenv MANPATH ${HOMEBREW_PREFIX}/share/man\`[ \${?MANPATH} == 1 ] && echo \":\${MANPATH}\"\`:;"
+      echo "setenv INFOPATH ${HOMEBREW_PREFIX}/share/info\`[ \${?INFOPATH} == 1 ] && echo \":\${INFOPATH}\"\`;"
       ;;
     *)
-      echo "export HOMEBREW_PREFIX=\"$HOMEBREW_PREFIX\";"
-      echo "export HOMEBREW_CELLAR=\"$HOMEBREW_CELLAR\";"
-      echo "export HOMEBREW_REPOSITORY=\"$HOMEBREW_REPOSITORY\";"
-      echo "export PATH=\"$HOMEBREW_PREFIX/bin:$HOMEBREW_PREFIX/sbin\${PATH+:\$PATH}\";"
-      echo "export MANPATH=\"$HOMEBREW_PREFIX/share/man\${MANPATH+:\$MANPATH}:\";"
-      echo "export INFOPATH=\"$HOMEBREW_PREFIX/share/info:\${INFOPATH:-}\";"
+      echo "export HOMEBREW_PREFIX=\"${HOMEBREW_PREFIX}\";"
+      echo "export HOMEBREW_CELLAR=\"${HOMEBREW_CELLAR}\";"
+      echo "export HOMEBREW_REPOSITORY=\"${HOMEBREW_REPOSITORY}\";"
+      echo "export PATH=\"${HOMEBREW_PREFIX}/bin:${HOMEBREW_PREFIX}/sbin\${PATH+:\$PATH}\";"
+      echo "export MANPATH=\"${HOMEBREW_PREFIX}/share/man\${MANPATH+:\$MANPATH}:\";"
+      echo "export INFOPATH=\"${HOMEBREW_PREFIX}/share/info:\${INFOPATH:-}\";"
       ;;
   esac
 }