CocoaPodsのバージョンチェックを実行しました。

$ pod --version
Ignoring json-1.8.6 because its extensions are not built. Try: gem pristine json --version 1.8.6
…
Ignoring unf_ext-0.0.7.7 because its extensions are not built. Try: gem pristine unf_ext --version 0.0.7.7
1.8.4
</code></pre>

なにかワーニングが出てしまっていますが、バージョン v1.8.4 がインストールされているようです。

 次に、CocoaPodsのインストールを実行しました。

<pre><code>
$ brew install cocoapods
Error: Can't create update lock in /usr/local/var/homebrew/locks!
Fix permissions by running:
  sudo chown -R $(whoami) /usr/local/var/homebrew
…

ユーザ権限系エラーになって、正常に実行できませんでした。

インストール時の警告の通り、chownでオーナー変更しました

$ sudo chown -R $(whoami) /usr/local/var/homebrew
$ brew install cocoapods
Warning: No remote 'origin' in /usr/local/Homebrew, skipping update!
Warning: No remote 'origin' in /usr/local/Homebrew/Library/Taps/caskformula/homebrew-caskformula, skipping update!
Warning: No remote 'origin' in /usr/local/Homebrew/Library/Taps/mono0926/homebrew-license-plist, skipping update!
==> Homebrew collects anonymous analytics.
Read the analytics documentation (and how to opt-out) here:
  https://docs.brew.sh/Analytics
No analytics have been recorded yet (nor will be during this `brew` run).

fatal: not in a git directory
Error: Command failed with exit 128: git
Warning: Treating cocoapods as a formula. For the cask, use homebrew/cask/cocoapods
Error: The following directories are not writable by your user:
…
Error: undefined method `[]' for nil:NilClass
Please report this issue:
  https://docs.brew.sh/Troubleshooting
/usr/local/Homebrew/Library/Homebrew/utils/analytics.rb:316:in `default_fields_influx'
/usr/local/Homebrew/Library/Homebrew/utils/analytics.rb:39:in `report_influx'
/usr/local/Homebrew/Library/Homebrew/utils/analytics.rb:87:in `report_influx_event'
/usr/local/Homebrew/Library/Homebrew/utils/analytics.rb:76:in `report_event'
…

他の権限エラーになって、まだ正常に実行できませんでした。

fatal: not in a git directoryの警告と、ネット検索した結果、Homebrewが管理しているgitの操作がインストール時にできていないっぽいので、git resetを実行しました。

$ git config --global --add safe.directory /usr/local/Homebrew
$ cd "$(brew --repository)"
$ git reset --hard FETCH_HEAD
fatal: Unable to create '/usr/local/Homebrew/.git/index.lock': Permission denied
</code></pre>
$(brew --repository)の配下のファイル・フォルダのオーナーが自身と別ユーザ担っていたため、chownでオーナーを自身に変更しました。その後、git resetを実行しました。
<pre><code>
$ git reset --hard FETCH_HEAD
HEAD is now at 4564628ea Merge pull request #15896 from branchvincent/pypi-excludes

git resetは成功したので、次にライブラリフォルダ内のデータをクリーンにします。

$ cd "$(brew --repository)/Library"
$ git clean -fd

gitリポジトリは、クリーンな状態なので、Homebrewを更新で正常に実行できるはずです。

brew update、brew upgradeで更新させました。

$ brew update
fatal: couldn't find remote ref refs/heads/master
To restore the stashed changes to /usr/local/Homebrew, run:
  cd /usr/local/Homebrew && git stash pop
Error: Fetching /usr/local/Homebrew/Library/Taps/mono0926/homebrew-license-plist failed!
Installing from the API is now the default behaviour!
You can save space and time by running:
  brew untap homebrew/core
Error: Some taps failed to update!
The following taps can not read their remote branches:
  mono0926/license-plist
This is happening because the remote branch was renamed or deleted.
Reset taps to point to the correct remote branches by running `brew tap --repair`
$ brew upgrade
==> Upgrading 45 outdated packages:
tree 1.8.0 -> 2.1.1_1
…
==> Upgrading readline
  8.2.1 -> 8.2.7 
…
==> Pouring carthage--0.39.1.ventura.bottle.tar.gz
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink bin/carthage
Target /usr/local/bin/carthage
already exists. You may want to remove it:
  rm '/usr/local/bin/carthage'

To force the link and overwrite all conflicting files:
  brew link --overwrite carthage

To list all files that would be deleted:
  brew link --overwrite --dry-run carthage

Possible conflicting files are:
/usr/local/bin/carthage
…
==> carthage
zsh completions have been installed to:
  /usr/local/share/zsh/site-functions
==> subversion
svntools have been installed to:
  /usr/local/opt/subversion/libexec

The perl bindings are located in various subdirectories of:
  /usr/local/opt/subversion/lib/perl5

警告は出てましたが、Homebrewの更新自体は、成功しました。

失敗した場合の参考例として、権限系がおかしな場合、brew upgradeでError: Failure...が出力されました。

$ brew update
f