$ brew install emacs --cocoa
==> Downloading
Already downloaded: /Library/Caches/Homebrew/emacs-24.3.tar.gz
==> ./configure --prefix=/usr/local/Cellar/emacs/24.3 --without-dbus --enable-locallisppath=/usr/local/share/emacs/site-lisp --infodir=/usr/local/Cellar/emacs/24.3/share/info/emacs --without-gnutls --with-n
==> make
==> make install
==> Caveats was installed to:

 To link the application to a normal Mac OS X location:
   brew linkapps
   ln -s /usr/local/Cellar/emacs/24.3/ /Applications

 A command line wrapper for the cocoa app was installed to:
Warning: Could not link emacs. Unlinking...
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
You can try again using `brew link emacs'

Possible conflicting files are:
/usr/local/bin/etags -> /usr/local/Cellar/emacs/HEAD/bin/etags
/usr/local/bin/emacsclient -> /usr/local/Cellar/emacs/HEAD/bin/emacsclient
/usr/local/bin/emacs -> /usr/local/Cellar/emacs/HEAD/bin/emacs
==> Summary
🍺  /usr/local/Cellar/emacs/24.3: 3851 files, 111M, built in 2.6 minutes
$ brew link emacs
Linking /usr/local/Cellar/emacs/24.3... Warning: Could not link emacs. Unlinking...

Error: Could not symlink file: /usr/local/Cellar/emacs/24.3/bin/etags
Target /usr/local/bin/etags already exists as a symlink to ../Cellar/emacs/HEAD/bin/etags.
If this file is from another formula, you may need to
`brew unlink` it. Otherwise, you may want to delete it.
To force the link and overwrite all other conflicting files, do:
  brew link --overwrite formula_name

To list all files that would be deleted:
  brew link --overwrite --dry-run formula_name
$  brew link emacs  --overwrite --dry-run emacs
Would remove:
/usr/local/bin/etags -> /usr/local/Cellar/emacs/HEAD/bin/etags
/usr/local/bin/emacsclient -> /usr/local/Cellar/emacs/HEAD/bin/emacsclient
/usr/local/bin/emacs -> /usr/local/Cellar/emacs/HEAD/bin/emacs

$ brew link emacs  --overwrite emacs
Linking /usr/local/Cellar/emacs/24.3... 21 symlinks created

$  cp -rf /usr/local/Cellar/emacs/24.3/ /Applications/