diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 44bc124540..d57ad2e399 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -82,7 +82,9 @@ HOMEBREW_TEMP="${HOMEBREW_TEMP:-${HOMEBREW_DEFAULT_TEMP}}"
 # Don't need to handle a default case.
 # HOMEBREW_LIBRARY set by bin/brew
 # shellcheck disable=SC2249,SC2154
-case "$*" in
+#
+# commands that take a single or no arguments.
+case "$1" in
   --cellar)
     echo "${HOMEBREW_CELLAR}"
     exit 0
@@ -99,12 +101,6 @@ case "$*" in
     echo "${HOMEBREW_CACHE}"
     exit 0
     ;;
-  shellenv)
-    source "${HOMEBREW_LIBRARY}/Homebrew/cmd/shellenv.sh"
-    shift
-    homebrew-shellenv "$1"
-    exit 0
-    ;;
   formulae)
     source "${HOMEBREW_LIBRARY}/Homebrew/cmd/formulae.sh"
     homebrew-formulae
@@ -115,6 +111,21 @@ case "$*" in
     homebrew-casks
     exit 0
     ;;
+  shellenv)
+    source "${HOMEBREW_LIBRARY}/Homebrew/cmd/shellenv.sh"
+    shift
+    homebrew-shellenv "$1"
+    exit 0
+    ;;
+  setup-ruby)
+    source "${HOMEBREW_LIBRARY}/Homebrew/cmd/setup-ruby.sh"
+    shift
+    homebrew-setup-ruby "$1"
+    exit 0
+    ;;
+esac
+# functions that take multiple arguments or handle multiple commands.
+case "$@" in
   # falls back to cmd/--prefix.rb and cmd/--cellar.rb on a non-zero return
   --prefix* | --cellar*)
     source "${HOMEBREW_LIBRARY}/Homebrew/formula_path.sh"
@@ -497,7 +508,8 @@ HOMEBREW_CORE_REPOSITORY="${HOMEBREW_LIBRARY}/Taps/homebrew/homebrew-core"
 # shellcheck disable=SC2034
 HOMEBREW_CASK_REPOSITORY="${HOMEBREW_LIBRARY}/Taps/homebrew/homebrew-cask"
 
-case "$*" in
+# commands that take a single or no arguments.
+case "$1" in
   --version | -v)
     source "${HOMEBREW_LIBRARY}/Homebrew/cmd/--version.sh"
     homebrew-version
diff --git a/Library/Homebrew/cmd/setup-ruby.sh b/Library/Homebrew/cmd/setup-ruby.sh
index d677899dfd..e39d893909 100644
--- a/Library/Homebrew/cmd/setup-ruby.sh
+++ b/Library/Homebrew/cmd/setup-ruby.sh
@@ -1,6 +1,8 @@
-#:  * `setup-ruby`
+#:  * `setup-ruby [command]`
 #:
 #:  Installs and configures Homebrew's Ruby.
+#:  If `command` is passed, it will only run Bundler if necessary for that
+#:  command.
 #:
 
 # HOMEBREW_LIBRARY is from the user environment.
@@ -12,11 +14,29 @@ homebrew-setup-ruby() {
   source "${HOMEBREW_LIBRARY}/Homebrew/utils/ruby.sh"
   setup-ruby-path
 
-  if [[ -z "${HOMEBREW_DEVELOPER}" && -z "${HOMEBREW_RUBY3}" ]]
+  if [[ -z "${HOMEBREW_DEVELOPER}" ]]
   then
     return
   fi
 
+  # Avoid running Bundler if the command doesn't need it.
+  local command="$1"
+  if [[ -n "${command}" ]]
+  then
+    source "${HOMEBREW_LIBRARY}/Homebrew/command_path.sh"
+
+    command_path="$(homebrew-command-path "${command}")"
+    if [[ -n "${command_path}" && "${command_path}" != *"/dev-cmd/"* ]]
+    then
+      return
+    fi
+
+    if ! grep -q "Homebrew.install_bundler_gems\!" "${command_path}"
+    then
+      return
+    fi
+  fi
+
   GEM_VERSION="$("${HOMEBREW_RUBY_PATH}" "${HOMEBREW_RUBY_DISABLE_OPTIONS}" /dev/stdin <<<'require "rbconfig"; puts RbConfig::CONFIG["ruby_version"]')"
   echo "${GEM_VERSION}"
   GEM_HOME="${HOMEBREW_LIBRARY}/Homebrew/vendor/bundle/ruby/${GEM_VERSION}"
diff --git a/Library/Homebrew/command_path.sh b/Library/Homebrew/command_path.sh
index b3288a7adc..362b654abe 100644
--- a/Library/Homebrew/command_path.sh
+++ b/Library/Homebrew/command_path.sh
@@ -6,7 +6,8 @@ homebrew-command-path() {
   case "$1" in
     # check we actually have command and not e.g. commandsomething
     command) ;;
-    *) return 1 ;;
+    command*) return 1 ;;
+    *) ;;
   esac
 
   local first_command found_command
diff --git a/Library/Homebrew/rubocops/all.rb b/Library/Homebrew/rubocops/all.rb
index 7c92c16e59..b42f50665e 100644
--- a/Library/Homebrew/rubocops/all.rb
+++ b/Library/Homebrew/rubocops/all.rb
@@ -12,6 +12,7 @@ require_relative "presence"
 require_relative "present"
 require_relative "safe_navigation_with_blank"
 require_relative "shell_commands"
+require_relative "install_bundler_gems"
 
 # formula audit cops
 require_relative "bottle"
diff --git a/Library/Homebrew/rubocops/extend/formula_cop.rb b/Library/Homebrew/rubocops/extend/formula_cop.rb
index 02f1ad1ec1..b443c5e615 100644
--- a/Library/Homebrew/rubocops/extend/formula_cop.rb
+++ b/Library/Homebrew/rubocops/extend/formula_cop.rb
@@ -20,7 +20,7 @@ module RuboCop
 
       # This method is called by RuboCop and is the main entry point.
       def on_class(node)
-        @file_path = processed_source.buffer.name
+        @file_path = processed_source.file_path
         return unless file_path_allowed?
         return unless formula_class?(node)
 
@@ -228,10 +228,9 @@ module RuboCop
       end
 
       def file_path_allowed?
-        paths_to_exclude = [%r{/Library/Homebrew/test/}]
         return true if @file_path.nil? # file_path is nil when source is directly passed to the cop, e.g. in specs
 
-        !@file_path.match?(Regexp.union(paths_to_exclude))
+        !@file_path.include?("/Library/Homebrew/test/")
       end
 
       def on_system_methods
diff --git a/Library/Homebrew/rubocops/install_bundler_gems.rb b/Library/Homebrew/rubocops/install_bundler_gems.rb
new file mode 100644
index 0000000000..c65a2931a4
--- /dev/null
+++ b/Library/Homebrew/rubocops/install_bundler_gems.rb
@@ -0,0 +1,21 @@
+# typed: true
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Homebrew
+      # Enforces the use of `Homebrew.install_bundler_gems!` in dev-cmd.
+      class InstallBundlerGems < Base
+        MSG = "Only use `Homebrew.install_bundler_gems!` in dev-cmd."
+        RESTRICT_ON_SEND = [:install_bundler_gems!].freeze
+
+        def on_send(node)
+          file_path = processed_source.file_path
+          return if file_path.match?(%r{/(dev-cmd/.+|standalone/init|startup/bootsnap)\.rb\z})
+
+          add_offense(node)
+        end
+      end
+    end
+  end
+end
diff --git a/Library/Homebrew/test/rubocops/install_bundler_gems_spec.rb b/Library/Homebrew/test/rubocops/install_bundler_gems_spec.rb
new file mode 100644
index 0000000000..032ddd5c25
--- /dev/null
+++ b/Library/Homebrew/test/rubocops/install_bundler_gems_spec.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "rubocops/install_bundler_gems"
+
+RSpec.describe RuboCop::Cop::Homebrew::InstallBundlerGems, :config do
+  it "registers an offense and corrects when using `Homebrew.install_bundler_gems!`" do
+    expect_offense(<<~RUBY)
+      Homebrew.install_bundler_gems!
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Only use `Homebrew.install_bundler_gems!` in dev-cmd.
+    RUBY
+  end
+end