From f999a57620d761065415bcd2d2a4141208a96eb9 Mon Sep 17 00:00:00 2001
From: Mike McQuaid <mike@mikemcquaid.com>
Date: Sat, 4 Nov 2017 16:30:54 +0000
Subject: [PATCH] brew.sh: cleanup some environment pollution.

---
 Library/Homebrew/brew.sh | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 241fa1c2e8..1e2b0f3ed8 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -69,9 +69,15 @@ then
   odie "Cowardly refusing to continue at this prefix: $HOMEBREW_PREFIX"
 fi
 
-# Save value to use for installing gems
-export HOMEBREW_GEM_HOME="$GEM_HOME"
-export HOMEBREW_GEM_PATH="$GEM_PATH"
+# Save values to use for installing gems
+if [[ -n "$GEM_HOME" ]]
+then
+  export HOMEBREW_GEM_HOME="$GEM_HOME"
+fi
+if [[ -n "$GEM_PATH" ]]
+then
+  export HOMEBREW_GEM_PATH="$GEM_PATH"
+fi
 
 # Users may have these set, pointing the system Ruby
 # at non-system gem paths
@@ -308,9 +314,6 @@ update-preinstall() {
   [[ -z "$HOMEBREW_NO_AUTO_UPDATE" ]] || return
   [[ -z "$HOMEBREW_UPDATE_PREINSTALL" ]] || return
 
-  # Allow auto-update migration now we have a fix in place (below in this function).
-  export HOMEBREW_ENABLE_AUTO_UPDATE_MIGRATION="1"
-
   if [[ "$HOMEBREW_COMMAND" = "install" || "$HOMEBREW_COMMAND" = "upgrade" || "$HOMEBREW_COMMAND" = "tap" ]]
   then
     if [[ -z "$HOMEBREW_VERBOSE" ]]
@@ -319,6 +322,9 @@ update-preinstall() {
       timer_pid=$!
     fi
 
+    # Allow auto-update migration now we have a fix in place (below in this function).
+    export HOMEBREW_ENABLE_AUTO_UPDATE_MIGRATION="1"
+
     brew update --preinstall
 
     if [[ -n "$timer_pid" ]]