From 3c5f007bfa1a469ef3e1a048ee163f3eaa73cb71 Mon Sep 17 00:00:00 2001
From: Martin Afanasjew <martin@afanasjew.de>
Date: Wed, 29 Jun 2016 16:20:47 +0200
Subject: [PATCH] bin/brew: fix corner cases in prefix computation

If `bin/brew` happens to be symlinked to `/brew`, `/bin/brew`, or some
similar location or (worse yet) Homebrew is installed to `/`, then
computation of the prefix and/or repository path could break down and
result in an invalid or empty path.

Closes Homebrew/homebrew-core#2430.
---
 bin/brew | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/bin/brew b/bin/brew
index b49b961e12..77611c153d 100755
--- a/bin/brew
+++ b/bin/brew
@@ -5,10 +5,13 @@ quiet_cd() {
   cd "$@" >/dev/null
 }
 
-BREW_FILE_DIRECTORY="$(quiet_cd "${0%/*}" && pwd -P)"
-HOMEBREW_BREW_FILE="$BREW_FILE_DIRECTORY/${0##*/}"
+BREW_FILE_DIRECTORY="$(quiet_cd "${0%/*}/" && pwd -P)"
+HOMEBREW_BREW_FILE="${BREW_FILE_DIRECTORY%/}/${0##*/}"
 
 HOMEBREW_PREFIX="${HOMEBREW_BREW_FILE%/*/*}"
+[[ -n "$HOMEBREW_PREFIX" && "$HOMEBREW_PREFIX" != "$HOMEBREW_BREW_FILE" ]] \
+  || HOMEBREW_PREFIX="/"
+
 HOMEBREW_REPOSITORY="$HOMEBREW_PREFIX"
 
 if [[ -L "$HOMEBREW_BREW_FILE" ]]