diff --git a/Library/Homebrew/brew.rb b/Library/Homebrew/brew.rb
index ca712613e4..a6299cdc44 100644
--- a/Library/Homebrew/brew.rb
+++ b/Library/Homebrew/brew.rb
@@ -85,16 +85,14 @@ begin
   ENV["PATH"] = path
 
   require "commands"
+  require "settings"
 
   if cmd
     internal_cmd = Commands.valid_internal_cmd?(cmd)
     internal_cmd ||= begin
       internal_dev_cmd = Commands.valid_internal_dev_cmd?(cmd)
       if internal_dev_cmd && !Homebrew::EnvConfig.developer?
-        if (HOMEBREW_REPOSITORY/".git/config").exist?
-          system "git", "config", "--file=#{HOMEBREW_REPOSITORY}/.git/config",
-                 "--replace-all", "homebrew.devcmdrun", "true"
-        end
+        Homebrew::Settings.write "devcmdrun", true
         ENV["HOMEBREW_DEV_CMD_RUN"] = "1"
       end
       internal_dev_cmd
diff --git a/Library/Homebrew/cmd/completions.rb b/Library/Homebrew/cmd/completions.rb
new file mode 100644
index 0000000000..3aad3aa9c8
--- /dev/null
+++ b/Library/Homebrew/cmd/completions.rb
@@ -0,0 +1,52 @@
+# typed: true
+# frozen_string_literal: true
+
+require "cli/parser"
+require "completions"
+
+module Homebrew
+  extend T::Sig
+
+  module_function
+
+  sig { returns(CLI::Parser) }
+  def completions_args
+    Homebrew::CLI::Parser.new do
+      usage_banner <<~EOS
+        `completions` [<subcommand>]
+
+        Control whether Homebrew automatically links external tap shell completion files.
+        Read more at <https://docs.brew.sh/Shell-Completion>.
+
+        `brew completions` [`state`]:
+        Display the current state of Homebrew's completions.
+
+        `brew completions` (`link`|`unlink`):
+        Link or unlink Homebrew's completions.
+      EOS
+
+      max_named 1
+    end
+  end
+
+  def completions
+    args = completions_args.parse
+
+    case args.named.first
+    when nil, "state"
+      if Completions.link_completions?
+        puts "Completions are linked."
+      else
+        puts "Completions are not linked."
+      end
+    when "link"
+      Completions.link!
+      puts "Completions are now linked."
+    when "unlink"
+      Completions.unlink!
+      puts "Completions are no longer linked."
+    else
+      raise UsageError, "unknown subcommand: #{args.named.first}"
+    end
+  end
+end
diff --git a/Library/Homebrew/cmd/update-report.rb b/Library/Homebrew/cmd/update-report.rb
index f38b341394..3a91124812 100644
--- a/Library/Homebrew/cmd/update-report.rb
+++ b/Library/Homebrew/cmd/update-report.rb
@@ -8,6 +8,7 @@ require "descriptions"
 require "cleanup"
 require "description_cache_store"
 require "cli/parser"
+require "settings"
 
 module Homebrew
   extend T::Sig
@@ -63,16 +64,12 @@ module Homebrew
       Utils::Analytics.messages_displayed! if $stdout.tty?
     end
 
-    HOMEBREW_REPOSITORY.cd do
-      donation_message_displayed =
-        Utils.popen_read("git", "config", "--get", "homebrew.donationmessage").chomp == "true"
-      if !donation_message_displayed && !args.quiet?
-        ohai "Homebrew is run entirely by unpaid volunteers. Please consider donating:"
-        puts "  #{Formatter.url("https://github.com/Homebrew/brew#donations")}\n"
+    if Settings.read("donationmessage") != "true" && !args.quiet?
+      ohai "Homebrew is run entirely by unpaid volunteers. Please consider donating:"
+      puts "  #{Formatter.url("https://github.com/Homebrew/brew#donations")}\n"
 
-        # Consider the message possibly missed if not a TTY.
-        safe_system "git", "config", "--replace-all", "homebrew.donationmessage", "true" if $stdout.tty?
-      end
+      # Consider the message possibly missed if not a TTY.
+      Settings.write "donationmessage", true if $stdout.tty?
     end
 
     install_core_tap_if_necessary
@@ -89,19 +86,14 @@ module Homebrew
       puts "Updated Homebrew from #{shorten_revision(initial_revision)} to #{shorten_revision(current_revision)}."
       updated = true
 
-      old_tag = if (HOMEBREW_REPOSITORY/".git/config").exist?
-        Utils.popen_read(
-          "git", "config", "--file=#{HOMEBREW_REPOSITORY}/.git/config", "--get", "homebrew.latesttag"
-        ).chomp.presence
-      end
+      old_tag = Settings.read "latesttag"
 
       new_tag = Utils.popen_read(
         "git", "-C", HOMEBREW_REPOSITORY, "tag", "--list", "--sort=-version:refname", "*.*"
       ).lines.first.chomp
 
       if new_tag != old_tag
-        system "git", "config", "--file=#{HOMEBREW_REPOSITORY}/.git/config",
-               "--replace-all", "homebrew.latesttag", new_tag
+        Settings.write "latesttag", new_tag
         new_repository_version = new_tag
       end
     end
diff --git a/Library/Homebrew/completions.rb b/Library/Homebrew/completions.rb
new file mode 100644
index 0000000000..880ac0d8e4
--- /dev/null
+++ b/Library/Homebrew/completions.rb
@@ -0,0 +1,69 @@
+# typed: true
+# frozen_string_literal: true
+
+require "utils/link"
+require "settings"
+
+module Homebrew
+  # Helper functions for generating shell completions.
+  #
+  # @api private
+  module Completions
+    extend T::Sig
+
+    module_function
+
+    SHELLS = %w[bash fish zsh].freeze
+
+    sig { void }
+    def link!
+      Settings.write :linkcompletions, true
+      Tap.each do |tap|
+        Utils::Link.link_completions tap.path, "brew completions link"
+      end
+    end
+
+    sig { void }
+    def unlink!
+      Settings.write :linkcompletions, false
+      Tap.each do |tap|
+        next if tap.official?
+
+        Utils::Link.unlink_completions tap.path
+      end
+    end
+
+    sig { returns(T::Boolean) }
+    def link_completions?
+      Settings.read(:linkcompletions) == "true"
+    end
+
+    sig { returns(T::Boolean) }
+    def completions_to_link?
+      Tap.each do |tap|
+        next if tap.official?
+
+        SHELLS.each do |shell|
+          return true if (tap.path/"completions/#{shell}").exist?
+        end
+      end
+
+      false
+    end
+
+    sig { void }
+    def show_completions_message_if_needed
+      return if Settings.read(:completionsmessageshown) == "true"
+      return unless completions_to_link?
+
+      ohai "Homebrew completions for external commands are unlinked by default!"
+      puts <<~EOS
+        To opt-in to automatically linking external tap shell competion files, run:
+          brew completions link
+        Then, follow the directions at #{Formatter.url("https://docs.brew.sh/Shell-Completion")}
+      EOS
+
+      Settings.write :completionsmessageshown, true
+    end
+  end
+end
diff --git a/Library/Homebrew/completions.rbi b/Library/Homebrew/completions.rbi
new file mode 100644
index 0000000000..8c4746bcaf
--- /dev/null
+++ b/Library/Homebrew/completions.rbi
@@ -0,0 +1,7 @@
+# typed: strict
+
+module Homebrew
+  module Completions
+    include Kernel
+  end
+end
diff --git a/Library/Homebrew/settings.rb b/Library/Homebrew/settings.rb
new file mode 100644
index 0000000000..30d5567bd5
--- /dev/null
+++ b/Library/Homebrew/settings.rb
@@ -0,0 +1,41 @@
+# typed: true
+# frozen_string_literal: true
+
+module Homebrew
+  # Helper functions for reading and writing settings.
+  #
+  # @api private
+  module Settings
+    extend T::Sig
+
+    module_function
+
+    sig { params(setting: T.any(String, Symbol), repo: Pathname).returns(T.nilable(String)) }
+    def read(setting, repo: HOMEBREW_REPOSITORY)
+      return unless (repo/".git/config").exist?
+
+      repo.cd do
+        Utils.popen_read("git", "config", "--get", "homebrew.#{setting}").chomp.presence
+      end
+    end
+
+    sig { params(setting: T.any(String, Symbol), value: T.any(String, T::Boolean), repo: Pathname).void }
+    def write(setting, value, repo: HOMEBREW_REPOSITORY)
+      return unless (repo/".git/config").exist?
+
+      repo.cd do
+        safe_system "git", "config", "--replace-all", "homebrew.#{setting}", value.to_s
+      end
+    end
+
+    sig { params(setting: T.any(String, Symbol), repo: Pathname).void }
+    def delete(setting, repo: HOMEBREW_REPOSITORY)
+      return unless (repo/".git/config").exist?
+      return if read(setting, repo: repo).blank?
+
+      repo.cd do
+        safe_system "git", "config", "--unset-all", "homebrew.#{setting}"
+      end
+    end
+  end
+end
diff --git a/Library/Homebrew/settings.rbi b/Library/Homebrew/settings.rbi
new file mode 100644
index 0000000000..289622fd41
--- /dev/null
+++ b/Library/Homebrew/settings.rbi
@@ -0,0 +1,7 @@
+# typed: strict
+
+module Homebrew
+  module Settings
+    include Kernel
+  end
+end
diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index a5e580249c..2e75f812fa 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -2,8 +2,10 @@
 # frozen_string_literal: true
 
 require "commands"
+require "completions"
 require "extend/cachable"
 require "description_cache_store"
+require "settings"
 
 # A {Tap} is used to extend the formulae provided by Homebrew core.
 # Usually, it's synced with a remote Git repository. And it's likely
@@ -340,7 +342,13 @@ class Tap
   def link_completions_and_manpages
     command = "brew tap --repair"
     Utils::Link.link_manpages(path, command)
-    Utils::Link.link_completions(path, command)
+
+    Homebrew::Completions.show_completions_message_if_needed
+    if official? || Homebrew::Completions.link_completions?
+      Utils::Link.link_completions(path, command)
+    else
+      Utils::Link.unlink_completions(path)
+    end
   end
 
   # Uninstall this {Tap}.
@@ -814,18 +822,14 @@ class TapConfig
     return unless tap.git?
     return unless Utils::Git.available?
 
-    tap.path.cd do
-      Utils.popen_read("git", "config", "--get", "homebrew.#{key}").chomp.presence
-    end
+    Homebrew::Settings.read key, repo: tap.path
   end
 
   def []=(key, value)
     return unless tap.git?
     return unless Utils::Git.available?
 
-    tap.path.cd do
-      safe_system "git", "config", "--replace-all", "homebrew.#{key}", value.to_s
-    end
+    Homebrew::Settings.write key, value.to_s, repo: tap.path
   end
 end
 
diff --git a/Library/Homebrew/test/cmd/completions_spec.rb b/Library/Homebrew/test/cmd/completions_spec.rb
new file mode 100644
index 0000000000..721fa184ae
--- /dev/null
+++ b/Library/Homebrew/test/cmd/completions_spec.rb
@@ -0,0 +1,22 @@
+# typed: false
+# frozen_string_literal: true
+
+require "cmd/shared_examples/args_parse"
+
+describe "brew completions" do
+  describe "Homebrew.completions_args" do
+    it_behaves_like "parseable arguments"
+  end
+
+  it "runs the status subcommand correctly", :integration_test do
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "init"
+    end
+
+    brew "completions", "link"
+    expect { brew "completions" }
+      .to output(/Completions are linked/).to_stdout
+      .and not_to_output.to_stderr
+      .and be_a_success
+  end
+end
diff --git a/Library/Homebrew/test/completions_spec.rb b/Library/Homebrew/test/completions_spec.rb
new file mode 100644
index 0000000000..efdcee115e
--- /dev/null
+++ b/Library/Homebrew/test/completions_spec.rb
@@ -0,0 +1,140 @@
+# typed: false
+# frozen_string_literal: true
+
+require "completions"
+
+describe Homebrew::Completions do
+  let(:internal_path) { HOMEBREW_REPOSITORY/"Library/Taps/homebrew/homebrew-bar" }
+  let(:external_path) { HOMEBREW_REPOSITORY/"Library/Taps/foo/homebrew-bar" }
+
+  before do
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "init"
+    end
+    internal_path.mkpath
+    external_path.mkpath
+  end
+
+  def setup_completions(external:)
+    (internal_path/"completions/bash/foo_internal").write "#foo completions"
+    if external
+      (external_path/"completions/bash/foo_external").write "#foo completions"
+    elsif (external_path/"completions/bash/foo_external").exist?
+      (external_path/"completions/bash/foo_external").delete
+    end
+  end
+
+  def setup_completions_setting(state, setting: "linkcompletions")
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "config", "--replace-all", "homebrew.#{setting}", state.to_s
+    end
+  end
+
+  def read_completions_setting(setting: "linkcompletions")
+    HOMEBREW_REPOSITORY.cd do
+      Utils.popen_read("git", "config", "--get", "homebrew.#{setting}").chomp.presence
+    end
+  end
+
+  def delete_completions_setting(setting: "linkcompletions")
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "config", "--unset-all", "homebrew.#{setting}"
+    end
+  end
+
+  after do
+    FileUtils.rm_rf internal_path
+    FileUtils.rm_rf external_path.dirname
+  end
+
+  describe ".link!" do
+    it "sets homebrew.linkcompletions to true" do
+      setup_completions_setting false
+      expect { described_class.link! }.not_to raise_error
+      expect(read_completions_setting).to eq "true"
+    end
+
+    it "sets homebrew.linkcompletions to true if unset" do
+      delete_completions_setting
+      expect { described_class.link! }.not_to raise_error
+      expect(read_completions_setting).to eq "true"
+    end
+
+    it "keeps homebrew.linkcompletions set to true" do
+      setup_completions_setting true
+      expect { described_class.link! }.not_to raise_error
+      expect(read_completions_setting).to eq "true"
+    end
+  end
+
+  describe ".unlink!" do
+    it "sets homebrew.linkcompletions to false" do
+      setup_completions_setting true
+      expect { described_class.unlink! }.not_to raise_error
+      expect(read_completions_setting).to eq "false"
+    end
+
+    it "sets homebrew.linkcompletions to false if unset" do
+      delete_completions_setting
+      expect { described_class.unlink! }.not_to raise_error
+      expect(read_completions_setting).to eq "false"
+    end
+
+    it "keeps homebrew.linkcompletions set to false" do
+      setup_completions_setting false
+      expect { described_class.unlink! }.not_to raise_error
+      expect(read_completions_setting).to eq "false"
+    end
+  end
+
+  describe ".link_completions?" do
+    it "returns true if homebrew.linkcompletions is true" do
+      setup_completions_setting true
+      expect(described_class.link_completions?).to be true
+    end
+
+    it "returns false if homebrew.linkcompletions is false" do
+      setup_completions_setting false
+      expect(described_class.link_completions?).to be false
+    end
+
+    it "returns false if homebrew.linkcompletions is not set" do
+      expect(described_class.link_completions?).to be false
+    end
+  end
+
+  describe ".completions_to_link?" do
+    it "returns false if only internal taps have completions" do
+      setup_completions external: false
+      expect(described_class.completions_to_link?).to be false
+    end
+
+    it "returns true if external taps have completions" do
+      setup_completions external: true
+      expect(described_class.completions_to_link?).to be true
+    end
+  end
+
+  describe ".show_completions_message_if_needed" do
+    it "doesn't show the message if there are no completions to link" do
+      setup_completions external: false
+      delete_completions_setting setting: :completionsmessageshown
+      expect { described_class.show_completions_message_if_needed }.not_to output.to_stdout
+    end
+
+    it "doesn't show the message if there are completions to link but the message has already been shown" do
+      setup_completions external: true
+      setup_completions_setting true, setting: :completionsmessageshown
+      expect { described_class.show_completions_message_if_needed }.not_to output.to_stdout
+    end
+
+    it "shows the message if there are completions to link and the message hasn't already been shown" do
+      setup_completions external: true
+      delete_completions_setting setting: :completionsmessageshown
+
+      message = /Homebrew completions for external commands are unlinked by default!/
+      expect { described_class.show_completions_message_if_needed }
+        .to output(message).to_stdout
+    end
+  end
+end
diff --git a/Library/Homebrew/test/settings_spec.rb b/Library/Homebrew/test/settings_spec.rb
new file mode 100644
index 0000000000..8df4063fc2
--- /dev/null
+++ b/Library/Homebrew/test/settings_spec.rb
@@ -0,0 +1,74 @@
+# typed: false
+# frozen_string_literal: true
+
+require "settings"
+
+describe Homebrew::Settings do
+  before do
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "init"
+    end
+  end
+
+  def setup_setting
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "config", "--replace-all", "homebrew.foo", "true"
+    end
+  end
+
+  describe ".read" do
+    it "returns the correct value for a setting" do
+      setup_setting
+      expect(described_class.read("foo")).to eq "true"
+    end
+
+    it "returns the correct value for a setting as a symbol" do
+      setup_setting
+      expect(described_class.read(:foo)).to eq "true"
+    end
+
+    it "returns nil when setting is not set" do
+      setup_setting
+      expect(described_class.read("bar")).to be_nil
+    end
+
+    it "runs on a repo without a configuration file" do
+      expect { described_class.read("foo", repo: HOMEBREW_REPOSITORY/"bar") }.not_to raise_error
+    end
+  end
+
+  describe ".write" do
+    it "writes over an existing value" do
+      setup_setting
+      described_class.write :foo, false
+      expect(described_class.read("foo")).to eq "false"
+    end
+
+    it "writes a new value" do
+      setup_setting
+      described_class.write :bar, "abcde"
+      expect(described_class.read("bar")).to eq "abcde"
+    end
+
+    it "returns if the repo doesn't have a configuration file" do
+      expect { described_class.write("foo", repo: HOMEBREW_REPOSITORY/"bar") }.not_to raise_error
+    end
+  end
+
+  describe ".delete" do
+    it "deletes an existing setting" do
+      setup_setting
+      described_class.delete(:foo)
+      expect(described_class.read("foo")).to be_nil
+    end
+
+    it "deletes a non-existing setting" do
+      setup_setting
+      expect { described_class.delete(:bar) }.not_to raise_error
+    end
+
+    it "returns if the repo doesn't have a configuration file" do
+      expect { described_class.delete("foo", repo: HOMEBREW_REPOSITORY/"bar") }.not_to raise_error
+    end
+  end
+end
diff --git a/Library/Homebrew/test/tap_spec.rb b/Library/Homebrew/test/tap_spec.rb
index 3a5ddf8197..691e5fa61c 100644
--- a/Library/Homebrew/test/tap_spec.rb
+++ b/Library/Homebrew/test/tap_spec.rb
@@ -84,6 +84,14 @@ describe Tap do
     end
   end
 
+  def setup_completion(link:)
+    HOMEBREW_REPOSITORY.cd do
+      system "git", "init"
+      system "git", "config", "--replace-all", "homebrew.linkcompletions", link.to_s
+      system "git", "config", "--replace-all", "homebrew.completionsmessageshown", "true"
+    end
+  end
+
   specify "::fetch" do
     expect(described_class.fetch("Homebrew", "core")).to be_kind_of(CoreTap)
     expect(described_class.fetch("Homebrew", "homebrew")).to be_kind_of(CoreTap)
@@ -285,6 +293,7 @@ describe Tap do
   specify "#install and #uninstall" do
     setup_tap_files
     setup_git_repo
+    setup_completion link: true
 
     tap = described_class.new("Homebrew", "bar")
 
@@ -308,9 +317,49 @@ describe Tap do
     (HOMEBREW_PREFIX/"share").rmtree if (HOMEBREW_PREFIX/"share").exist?
   end
 
-  specify "#link_completions_and_manpages" do
+  specify "#link_completions_and_manpages when completions are enabled for non-official tap" do
     setup_tap_files
     setup_git_repo
+    setup_completion link: true
+    tap = described_class.new("NotHomebrew", "baz")
+    tap.install clone_target: subject.path/".git"
+    (HOMEBREW_PREFIX/"share/man/man1/brew-tap-cmd.1").delete
+    (HOMEBREW_PREFIX/"etc/bash_completion.d/brew-tap-cmd").delete
+    (HOMEBREW_PREFIX/"share/zsh/site-functions/_brew-tap-cmd").delete
+    (HOMEBREW_PREFIX/"share/fish/vendor_completions.d/brew-tap-cmd.fish").delete
+    tap.link_completions_and_manpages
+    expect(HOMEBREW_PREFIX/"share/man/man1/brew-tap-cmd.1").to be_a_file
+    expect(HOMEBREW_PREFIX/"etc/bash_completion.d/brew-tap-cmd").to be_a_file
+    expect(HOMEBREW_PREFIX/"share/zsh/site-functions/_brew-tap-cmd").to be_a_file
+    expect(HOMEBREW_PREFIX/"share/fish/vendor_completions.d/brew-tap-cmd.fish").to be_a_file
+    tap.uninstall
+  ensure
+    (HOMEBREW_PREFIX/"etc").rmtree if (HOMEBREW_PREFIX/"etc").exist?
+    (HOMEBREW_PREFIX/"share").rmtree if (HOMEBREW_PREFIX/"share").exist?
+  end
+
+  specify "#link_completions_and_manpages when completions are disabled for non-official tap" do
+    setup_tap_files
+    setup_git_repo
+    setup_completion link: false
+    tap = described_class.new("NotHomebrew", "baz")
+    tap.install clone_target: subject.path/".git"
+    (HOMEBREW_PREFIX/"share/man/man1/brew-tap-cmd.1").delete
+    tap.link_completions_and_manpages
+    expect(HOMEBREW_PREFIX/"share/man/man1/brew-tap-cmd.1").to be_a_file
+    expect(HOMEBREW_PREFIX/"etc/bash_completion.d/brew-tap-cmd").not_to be_a_file
+    expect(HOMEBREW_PREFIX/"share/zsh/site-functions/_brew-tap-cmd").not_to be_a_file
+    expect(HOMEBREW_PREFIX/"share/fish/vendor_completions.d/brew-tap-cmd.fish").not_to be_a_file
+    tap.uninstall
+  ensure
+    (HOMEBREW_PREFIX/"etc").rmtree if (HOMEBREW_PREFIX/"etc").exist?
+    (HOMEBREW_PREFIX/"share").rmtree if (HOMEBREW_PREFIX/"share").exist?
+  end
+
+  specify "#link_completions_and_manpages when completions are enabled for official tap" do
+    setup_tap_files
+    setup_git_repo
+    setup_completion link: false
     tap = described_class.new("Homebrew", "baz")
     tap.install clone_target: subject.path/".git"
     (HOMEBREW_PREFIX/"share/man/man1/brew-tap-cmd.1").delete
diff --git a/Library/Homebrew/utils/analytics.rb b/Library/Homebrew/utils/analytics.rb
index 6dca9a2001..3d20136514 100644
--- a/Library/Homebrew/utils/analytics.rb
+++ b/Library/Homebrew/utils/analytics.rb
@@ -3,6 +3,7 @@
 
 require "context"
 require "erb"
+require "settings"
 
 module Utils
   # Helper module for fetching and reporting analytics data.
@@ -102,27 +103,27 @@ module Utils
       end
 
       def uuid
-        config_get(:analyticsuuid)
+        Homebrew::Settings.read :analyticsuuid
       end
 
       def messages_displayed!
-        config_set(:analyticsmessage, true)
-        config_set(:caskanalyticsmessage, true)
+        Homebrew::Settings.write :analyticsmessage, true
+        Homebrew::Settings.write :caskanalyticsmessage, true
       end
 
       def enable!
-        config_set(:analyticsdisabled, false)
+        Homebrew::Settings.write :analyticsdisabled, false
         messages_displayed!
       end
 
       def disable!
-        config_set(:analyticsdisabled, true)
+        Homebrew::Settings.write :analyticsdisabled, true
         regenerate_uuid!
       end
 
       def regenerate_uuid!
         # it will be regenerated in next run unless disabled.
-        config_delete(:analyticsuuid)
+        Homebrew::Settings.delete :analyticsuuid
       end
 
       def output(args:, filter: nil)
@@ -313,25 +314,7 @@ module Utils
       end
 
       def config_true?(key)
-        config_get(key) == "true"
-      end
-
-      def config_get(key)
-        HOMEBREW_REPOSITORY.cd do
-          Utils.popen_read("git", "config", "--get", "homebrew.#{key}").chomp
-        end
-      end
-
-      def config_set(key, value)
-        HOMEBREW_REPOSITORY.cd do
-          safe_system "git", "config", "--replace-all", "homebrew.#{key}", value.to_s
-        end
-      end
-
-      def config_delete(key)
-        HOMEBREW_REPOSITORY.cd do
-          system "git", "config", "--unset-all", "homebrew.#{key}"
-        end
+        Homebrew::Settings.read(key) == "true"
       end
 
       def formulae_brew_sh_json(endpoint)
diff --git a/completions/internal_commands_list.txt b/completions/internal_commands_list.txt
index f1a952a9e1..13e278cc73 100644
--- a/completions/internal_commands_list.txt
+++ b/completions/internal_commands_list.txt
@@ -25,6 +25,7 @@ cat
 cleanup
 command
 commands
+completions
 config
 configure
 create
diff --git a/docs/Manpage.md b/docs/Manpage.md
index bda3f0502c..7061af5693 100644
--- a/docs/Manpage.md
+++ b/docs/Manpage.md
@@ -94,6 +94,17 @@ Show lists of built-in and external commands.
 * `--include-aliases`:
   Include aliases of internal commands.
 
+### `completions` [*`subcommand`*]
+
+Control whether Homebrew automatically links external tap shell completion files.
+Read more at <https://docs.brew.sh/Shell-Completion>.
+
+`brew completions` [`state`]
+<br>Display the current state of Homebrew's completions.
+
+`brew completions` (`link`|`unlink`)
+<br>Link or unlink Homebrew's completions.
+
 ### `config`
 
 Show Homebrew and system configuration info useful for debugging. If you file
diff --git a/docs/Shell-Completion.md b/docs/Shell-Completion.md
index bb5aa592f5..b68d23744b 100644
--- a/docs/Shell-Completion.md
+++ b/docs/Shell-Completion.md
@@ -4,7 +4,9 @@ Homebrew comes with completion definitions for the `brew` command. Some packages
 
 `zsh`, `bash` and `fish` are currently supported.
 
-You must configure your shell to enable its completion support. This is because the Homebrew-managed completions are stored under `HOMEBREW_PREFIX` which your system shell may not be aware of, and since it is difficult to automatically configure `bash` and `zsh` completions in a robust manner, the Homebrew installer does not do it for you.
+You must then configure your shell to enable its completion support. This is because the Homebrew-managed completions are stored under `HOMEBREW_PREFIX` which your system shell may not be aware of, and since it is difficult to automatically configure `bash` and `zsh` completions in a robust manner, the Homebrew installer does not do it for you.
+
+Shell completions for external Homebrew commands are not automatically installed. To opt-in to using completions for external commands (if provided), they need to be linked to `HOMEBREW_PREFIX` by running `brew completions link`.
 
 ## Configuring Completions in `bash`
 
diff --git a/manpages/brew.1 b/manpages/brew.1
index 09132afcc7..3734944d13 100644
--- a/manpages/brew.1
+++ b/manpages/brew.1
@@ -93,6 +93,17 @@ List only the names of commands without category headers\.
 \fB\-\-include\-aliases\fR
 Include aliases of internal commands\.
 .
+.SS "\fBcompletions\fR [\fIsubcommand\fR]"
+Control whether Homebrew automatically links external tap shell completion files\. Read more at \fIhttps://docs\.brew\.sh/Shell\-Completion\fR\.
+.
+.P
+\fBbrew completions\fR [\fBstate\fR]
+    Display the current state of Homebrew\'s completions\.
+.
+.P
+\fBbrew completions\fR (\fBlink\fR|\fBunlink\fR)
+    Link or unlink Homebrew\'s completions\.
+.
 .SS "\fBconfig\fR"
 Show Homebrew and system configuration info useful for debugging\. If you file a bug report, you will be required to provide this information\.
 .