How Homebrew works?

Homebrew — The missing package manager for macOS. Here is the Official site: https://brew.sh

What is Homebrew?

Homebrew is a package manager for OS X. It allows a user to easily install software from the larger body of UNIX and open source software on the Mac. If you know linux, you can compare the brew command with the apt-get command (on Debian)

How to install?

Open terminal or iterm2 on your Mac and paste this line at a Terminal prompt.

 /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Homebrew Walkthrough by example

Install Screenfetch using brew:

  • Screenfetch is a Fetches system/theme information in terminal for Linux desktop screenshots.
  • It is a “Bash Screenshot Information Tool”. This handy Bash script can be used to generate one of those nifty terminal theme information + ASCII distribution logos you see in everyone’s screenshots nowadays. It will auto-detect your distribution and display an ASCII version of that distribution’s logo and some valuable information to the right. There are options to specify no ASCII art, colors, taking a screenshot upon displaying info, and even customizing the screenshot command! This script is very easy to add to and can easily be extended.
  • Install Screenfetch: brew install screenfetch
  • Now, you can use screenfetch command on your Mac
  • More information about screenfetch, see here: https://github.com/KittyKatt/screenFetch

Some packages of Linux that you can install on Mac using brew:

  • wget, coreutils, gcc, imagemagick, geoip
  • nmap https://nmap.org/
  • sqlmap http://sqlmap.org/
  • ncdu https://dev.yorhel.nl/ncdu
  • …

See all on Homebrew formulas index

How it works?

Overview:

  • Homebrew is based on Git and Ruby.
  • The first time you install it, it’ll set things up in /usr/local/ by default
  • Every time you run brew update it does a git pull
  • You can check all information about package like htop, you can using brew desc htop and brew info htop
DevOps at MacbookPro in /usr/local/Cellar/nmap/7.40
$ brew desc htop
htop: Improved top (interactive process viewer)
DevOps at MacbookPro in /usr/local/Cellar/nmap/7.40
$ brew info htop
htop: stable 2.0.2 (bottled), HEAD
Improved top (interactive process viewer)
https://hisham.hm/htop/
Conflicts with: htop-osx
/usr/local/Cellar/htop/2.0.2 (10 files, 183.8K) *
  Poured from bottle on 2017-01-15 at 02:50:09
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/htop.rb
==> Dependencies
Optional: homebrew/dupes/ncurses ✘
==> Options
--with-ncurses
	Build using homebrew ncurses (enables mouse scroll)
--HEAD
	Install HEAD version
==> Caveats
htop requires root privileges to correctly display all running processes,
so you will need to run `sudo htop`.
You should be certain that you trust any software you grant root privileges.
  • When you run brew install htop, Homebrew fetches the URL (here that’s https://homebrew.bintray.com/bottles/htop-2.0.2.sierra.bottle.tar.gz) using curl and stores the archive in a cache directory so you won’t download it twice
  • It computes its checksum and compares it against the one the formula provides, to ensure you’re downloading the right file.
  • Verifying htop-2.0.2.sierra.bottle.tar.gz checksum: sha256 179be9dccb80cee0c5e1a1f58c8f72ce7b2328ede30fb71dcdf336539be2f487
  • The development cutting edge of htop is decribled in url “https://github.com/hishamhm/htop.git”
  • One package can depend on other formulae; have patches and external resources; download stuff from Git, SVN, Mercurial or through FTP; and more.
  • Homebrew provide bottles (pre-built formulae); which are essentially formulae built by a bot then stored as a .tar.gz on a server so that you can download them directly instead of re-building everything from source every time. Bottles are defined in formulae and brew install use them when they’re available.
  • Need ncurses before install htop - optional
  • Here is htop.rb, it is a package definition written in Ruby. These formulae are Ruby files that describe the software they install and contain instructions to install and test it.
class Htop < Formula
  desc "Improved top (interactive process viewer)"
  homepage "https://hisham.hm/htop/"
  url "https://hisham.hm/htop/releases/2.0.2/htop-2.0.2.tar.gz"
  sha256 "179be9dccb80cee0c5e1a1f58c8f72ce7b2328ede30fb71dcdf336539be2f487"

  bottle do
    sha256 "555ff188b1990fb0a5b4634beef196ed1fb843336b99cac33d0291d592d93233" => :sierra
    sha256 "b13e6457905778a75d2627e1586e14ab20920001bed16b84c1fb64a258715741" => :el_capitan
    sha256 "f50fd11325a34da989c268f1e4bb998c4b8415079c23a95c267088e9576bef3e" => :yosemite
    sha256 "785c2806efe12a008c2fc958f567501e2931d2457261eed721ffae374f989498" => :mavericks
  end

  head do
    url "https://github.com/hishamhm/htop.git"

    depends_on "autoconf" => :build
    depends_on "automake" => :build
    depends_on "libtool" => :build
  end

  option "with-ncurses", "Build using homebrew ncurses (enables mouse scroll)"

  depends_on "homebrew/dupes/ncurses" => :optional

  conflicts_with "htop-osx", :because => "both install an `htop` binary"

  def install
    system "./autogen.sh" if build.head?
    system "./configure", "--prefix=#{prefix}"
    system "make", "install"
  end

  def caveats; <<-EOS.undent
    htop requires root privileges to correctly display all running processes,
    so you will need to run `sudo htop`.
    You should be certain that you trust any software you grant root privileges.
    EOS
  end

  test do
    pipe_output("#{bin}/htop", "q", 0)
  end
end

Reference

  1. https://www.quora.com/How-does-Homebrew-work-internally
  2. https://github.com/Homebrew/brew/blob/master/docs/Formula-Cookbook.md