macOSでv2系のHelmをインストールする

そんな日もあります。

```shell
$ brew install helm@2
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 3 taps (homebrew/core, homebrew/cask and aws/tap).
==> Updated Formulae
Updated 110 formulae.
==> New Casks
box-tools                          cloudflare-warp                    marathon-infinity                  marathon2
==> Updated Casks
1password-cli                      eloston-chromium                   mathpix-snipping-tool              sequel-ace
4k-stogram                         eve-launcher                       matterhorn                         shift
abstract                           final-cut-library-manager          microsoft-azure-storage-explorer   signal
activedock                         freeplane                          mongodb-compass                    sipgate-softphone
appcode                            grids                              mongodb-compass-isolated-edition   skype
audirvana                          http-toolkit                       mongodb-compass-readonly           slack
aws-vault                          ibored                             odrive                             slite
axure-rp                           icollections                       openphone                          snes9x
backblaze                          icq                                opera                              streamlabs-obs
baidunetdisk                       intune-company-portal              pagico                             supercollider
blender                            jami                               permute                            telavox-flow
bootstrap-studio                   joplin                             pixelsnap                          tiger-trade
bria                               keep-it                            plex                               ubersicht
cacher                             keysmith                           portfolioperformance               upwork
camo-studio                        kodelife                           privatevpn                         vmware-horizon-client
chef-workstation                   launchbar                          proclaim                           watchguard-mobile-vpn-with-ssl
chirp                              libreoffice                        qcad                               webots
cryo                               libreoffice-language-pack          quickhash                          whalebird
dcp-o-matic-batch-converter        loaf                               quip                               workflowy
downie                             logos                              refined-github-safari
dynobase                           mailmate                           remember-the-milk
element                            marginnote                         sensei
==> Deleted Casks
box-edit                                                              phiewer

==> Downloading https://homebrew.bintray.com/bottles/helm%402-2.16.10.catalina.bottle.tar.gz
==> Downloading from https://d29vzk4ow07wi7.cloudfront.net/c29eda468036c44de62924d971cbe13bb3073ac0306dce23dd1089173ce127c5?response-conten
######################################################################## 100.0%
==> Pouring helm@2-2.16.10.catalina.bottle.tar.gz
==> Caveats
helm@2 is keg-only, which means it was not symlinked into /usr/local,
because this is an alternate version of another formula.

If you need to have helm@2 first in your PATH run:
  echo 'export PATH="/usr/local/opt/helm@2/bin:$PATH"' >> ~/.zshrc


Bash completion has been installed to:
  /usr/local/opt/helm@2/etc/bash_completion.d

zsh completions have been installed to:
  /usr/local/opt/helm@2/share/zsh/site-functions
==> Summary
🍺  /usr/local/Cellar/helm@2/2.16.10: 51 files, 87.5MB

$ ls /uls /usr/local/Cellar/helm@2/2.16.10/bin 
helm   tiller

$ alias helm2=/usr/local/Cellar/helm@2/2.16.10/bin/helm
$ helm2 version
Client: &version.Version{SemVer:"v2.16.10", GitCommit:"bceca24a91639f045f22ab0f41e47589a932cf5e", GitTreeState:"clean"}
Server: &version.Version{SemVer:"v2.16.8", GitCommit:"145206680c1d5c28e3fcf30d6f596f0ba84fcb47", GitTreeState:"clean"}

$ helm version 
version.BuildInfo{Version:"v3.1.1", GitCommit:"afe70585407b420d0097d07b21c47dc511525ac8", GitTreeState:"clean", GoVersion:"go1.13.8"}
```

特定バージョン

```shell

$ curl -fsSL -o get_helm.sh https://raw.githubusercontent.com/helm/helm/master/scripts/get
$ chmod 700 get_helm.sh
$ ./get_helm.sh -v v2.13.0
```