Install old version using Homebrew

gistfile1.md

1. brew info [formula name] and look for From: to get url of current formula

$ brew info heroku                                                                                                                                                                                                 
heroku: stable 6.15.24 (bottled), HEAD
Command-line client for the cloud PaaS
https://cli.heroku.com
/usr/local/Cellar/heroku/3.42.10 (985 files, 6.2MB)
  Built from source on 2015-10-07 at 17:33:25
/usr/local/Cellar/heroku/3.42.20 (985 files, 6.2MB)
  Built from source on 2015-11-24 at 11:11:11
/usr/local/Cellar/heroku/3.42.22 (985 files, 6.2MB)
  Built from source on 2015-11-24 at 11:12:26
/usr/local/Cellar/heroku/3.43.2 (993 files, 6.2MB)
  Built from source on 2016-07-22 at 09:31:30
/usr/local/Cellar/heroku/6.11.3 (6,922 files, 73.1MB) *
  Built from source on 2017-08-04 at 10:33:41
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/heroku.rb
==> Dependencies
Required: node ✘
==> Options
--HEAD
	Install HEAD version

1. Go to: https://github.com/Homebrew/homebrew-core/blob/master/Formula/[formula name].rb example
2. Click "History" example
3. Find commit with version number you want. Usually the commit messages will have version numbers in them, if not, sorry. example
4. Click "View" to view the formula.rb file at that commit example
5. Click "Raw" to get direct link to file example
6. Install using url to the formula.rb you want to use: brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/15dde21700bd71e98eb0ba4afdf652f64063bbce/Formula/heroku.rb