Update based on comments (without a mutex...)

bin/brew

@@ -48,19 +48,14 @@ if [[ -n "$HOMEBREW_ENV_FILTERING" ]]
 then
   PATH="/usr/bin:/bin:/usr/sbin:/sbin"
 
-  export HOMEBREW_BREW_FILE
-  export HOMEBREW_PREFIX
-  export HOMEBREW_REPOSITORY
-  export HOMEBREW_LIBRARY
+#  export HOMEBREW_BREW_FILE
+#  export HOMEBREW_PREFIX
+#  export HOMEBREW_REPOSITORY
+#  export HOMEBREW_LIBRARY
 
   execution_env=()
   for key in HOME SHELL PATH TERM LOGNAME USER "${!HOMEBREW_@}"
   do
-    # ugly, unfortunate consequence of lack of `export -p NAME` in bash's export
-
-    # The following failed to find non exported vars on Bash 3.2.48
-    [[ "$(declare -p "$key" 2>/dev/null)" =~ ^declare\ -[^\ ]*x[^\ ]*\  ]] || continue
-
     execution_env+=( "${key}=${!key}" )
   done