HomebrewのFormulaのソースコードを確認する ref: http://qiita.com/shinespark/items/34a2980353c8f3bba30b

file0.txt

$ brew unpack tree
==> Unpacking tree to: /Users/metroid/tmp/tree-1.7.0
==> Downloading http://mama.indstate.edu/users/ice/tree/src/tree-1.7.0.tgz
Already downloaded: /Users/metroid/Library/Caches/Homebrew/tree-1.7.0.tgz
==> Verifying tree-1.7.0.tgz checksum
tar xzf /Users/metroid/Library/Caches/Homebrew/tree-1.7.0.tgz

$ ll
total 0
drwxr-xr-x   3 metroid  staff   102B 12 16 00:42 ./
drwxr-xr-x+ 78 metroid  staff   2.6K 12 16 00:42 ../
drwxr-xr-x  19 metroid  admin   646B 12 16 00:42 tree-1.7.0/

file1.txt

$ brew help unpack
brew unpack [--git|--patch] [--destdir=path] formulae:
    Unpack the source files for formulae into subdirectories of the current
    working directory. If --destdir=path is given, the subdirectories will
    be created in the directory named by path instead.

    If --patch is passed, patches for formulae will be applied to the
    unpacked source.

    If --git is passed, a Git repository will be initialized in the unpacked
    source. This is useful for creating patches for the software.