Add View The Source For A Brew Formula as a Unix TIL

unix/view-the-source-for-a-brew-formula.md

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+# View The Source For A Brew Formula
+
+[Homebrew](https://brew.sh/) uses formulas to know how to install things. If
+you want to see what a given thing's formula file (written in Ruby) looks like,
+there are two ways to get at it.
+
+If you already have the thing installed, the formula is available on your
+machine. You can `cat` it to stdout with `brew cat`.
+
+```bash
+❯ brew cat bat
+```
+
+Here is what `bat` looks like:
+
+```ruby
+class Bat < Formula
+  desc "Clone of cat(1) with syntax highlighting and Git integration"
+  homepage "https://github.com/sharkdp/bat"
+  url "https://github.com/sharkdp/bat/archive/v0.17.1.tar.gz"
+  sha256 "16d39414e8a3b80d890cfdbca6c0e6ff280058397f4a3066c37e0998985d87c4"
+  license "Apache-2.0"
+
+  depends_on "rust" => :build
+
+  uses_from_macos "zlib"
+
+  def install
+    ENV["SHELL_COMPLETIONS_DIR"] = buildpath
+    system "cargo", "install", *std_cargo_args
+
+    assets_dir = Dir["target/release/build/bat-*/out/assets"].first
+    man1.install "#{assets_dir}/manual/bat.1"
+    fish_completion.install "#{assets_dir}/completions/bat.fish"
+    zsh_completion.install "#{assets_dir}/completions/bat.zsh" => "_bat"
+  end
+
+  test do
+    pdf = test_fixtures("test.pdf")
+    output = shell_output("#{bin}/bat #{pdf} --color=never")
+    assert_match "Homebrew test", output
+  end
+end
+```
+
+If you don't have the thing installed, you'll have to access the formula
+remotely.
+
+```bash
+❯ brew info --github bat
+```
+
+This will open up the formula on GitHub in your default browser.