bin/brew: simplify filtering of BIN_BREW_EXPORTED_VARS

Looping over `BIN_BREW_EXPORTED_VARS` for each line of an env file is
relatively inefficient. We can avoid this by constructing a regex before
the loop and using that regex to match against the lines we want to
skip.

Author: carlocab

bin/brew

@@ -113,21 +113,23 @@ BIN_BREW_EXPORTED_VARS=(
 # Load Homebrew's variable configuration files from disk.
 export_homebrew_env_file() {
   local env_file
+  local bin_brew_exported_vars_regex
 
   env_file="${1}"
   [[ -r "${env_file}" ]] || return 0
+
+  bin_brew_exported_vars_regex="^($(
+    IFS='|'
+    echo "${BIN_BREW_EXPORTED_VARS[*]}"
+  ))"
+
   while read -r line
   do
     # only load variables defined in env_config.rb
     [[ "${line}" =~ ^(HOMEBREW_|SUDO_ASKPASS=|(all|no|ftp|https?)_proxy=) ]] || continue
 
     # forbid overriding variables that are set in this file
-    local invalid_variable
-    for VAR in "${BIN_BREW_EXPORTED_VARS[@]}"
-    do
-      [[ "${line}" = "${VAR}"* ]] && invalid_variable="${VAR}"
-    done
-    [[ -n "${invalid_variable:-}" ]] && continue
+    [[ "${line}" =~ ${bin_brew_exported_vars_regex} ]] && continue
 
     export "${line?}"
   done <"${env_file}"