diff --git a/Library/Homebrew/utils/shell_env.sh b/Library/Homebrew/utils/shell_env.sh
new file mode 100755
index 0000000000..fc7e1c9726
--- /dev/null
+++ b/Library/Homebrew/utils/shell_env.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+set +o posix
+
+IFS="="
+
+while read -r key value
+do
+  export "$key=$value"
+done < /tmp/homebrew-env
+
+# Need to reset IFS to default value for later shell functions like 'printf -v HOMEBREW_MACOS_VERSION_NUMERIC ...' to work
+unset IFS
+
+# HOMEBREW_LIBRARY will have been readded above having been added originally in 'bin/brew'
+source "$HOMEBREW_LIBRARY/Homebrew/brew.sh"
diff --git a/bin/brew b/bin/brew
index 593043f9f2..846758c30a 100755
--- a/bin/brew
+++ b/bin/brew
@@ -44,4 +44,82 @@ fi
 
 HOMEBREW_LIBRARY="$HOMEBREW_REPOSITORY/Library"
 
-source "$HOMEBREW_LIBRARY/Homebrew/brew.sh"
+# Refactor of code from '/Library/Homebrew/brew.sh'
+export HOMEBREW_BREW_FILE
+export HOMEBREW_PREFIX
+export HOMEBREW_REPOSITORY
+export HOMEBREW_LIBRARY
+
+# Set to system default value to avoid any possible later mis-direction based on the user's shell env
+export PATH=/usr/bin:/bin:/usr/sbin:/sbin
+
+# -------------------------------------------------------------------------------------------------------------------------
+# Setting 'HOMEBREW_OLD_ENV' would be removed with 'env -i' so would need to be passed as another arg to the 'env -i' cmd.
+
+# The resulting '/tmp/homebrew-env' for an update prior to install was 
+# (which may run into bash arg limits, so I suggest keeping the tmp file):
+
+#HOMEBREW_PROCESSOR=Intel
+#HOMEBREW_DEV_CMD_RUN=1
+#HOMEBREW_USER_AGENT=Homebrew/1.X.Y (Macintosh; Intel macOS 10.6.8)
+#HOMEBREW_UPDATE_BEFORE=f7bccee2145547d21b2629cab8b5fddff3299bda
+#HOMEBREW_LIBRARY=/usr/local/Homebrew/Library
+#HOMEBREW_COMMAND_DEPTH=2
+#TERM=xterm-color
+#HOMEBREW_OS_VERSION=macOS 10.6.8
+#HOMEBREW_UPDATE_AFTER_HOMEBREW_HOMEBREW_BUNDLE=a32e4559ef653c648426a4d52abdb570db09fccf
+#HOMEBREW_REPOSITORY=/usr/local/Homebrew
+#HOMEBREW_ENABLE_AUTO_UPDATE_MIGRATION=1
+#HOMEBREW_UPDATE_AFTER_HOMEBREW_HOMEBREW_CORE=350aa1a6b9f5d31dabb9d2cfeeffb960a64509e6
+#HOMEBREW_GIT_CONFIG_FILE=/usr/local/Homebrew/.git/config
+#HOMEBREW_RUBY_PATH=/usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/current/bin/ruby
+#HOMEBREW_NO_AUTO_UPDATE=1
+#HOMEBREW_UPDATE_BEFORE_HOMEBREW_HOMEBREW_CORE=9bc16f465e1d7697426dd6dad685d161f1f4ee1d
+#HOMEBREW_ANALYTICS_USER_UUID=B2E8D13A-443F-4686-B946-DE6C797064D7
+#HOMEBREW_CACHE=/Users/doug/Library/Caches/Homebrew
+#HOMEBREW_USER_AGENT_CURL=Homebrew/1.X.Y (Macintosh; Intel macOS 10.6.8) curl/7.52.1
+#PATH=/usr/bin:/bin:/usr/sbin:/sbin
+#HOMEBREW_UPDATE_BEFORE_HOMEBREW_HOMEBREW_VERSIONS=c94a1b18d5c2c198b4be302b604dd0c845a4344b
+#HOMEBREW_UPDATE_BEFORE_CASKROOM_HOMEBREW_CASK=258fd55c9c3d4fc3699753f363927c51a6fe9c18
+#HOMEBREW_UPDATE_BEFORE_HOMEBREW_HOMEBREW_BUNDLE=a32e4559ef653c648426a4d52abdb570db09fccf
+#HOMEBREW_BREW_FILE=/usr/local/bin/brew
+#HOMEBREW_MACOS_VERSION=10.6.8
+#HOMEBREW_ANALYTICS_ID=UA-76679469-1
+#HOMEBREW_UPDATE_AFTER_HOMEBREW_HOMEBREW_VERSIONS=c94a1b18d5c2c198b4be302b604dd0c845a4344b
+#HOMEBREW_UPDATE_AFTER_CASKROOM_HOMEBREW_CASK=258fd55c9c3d4fc3699753f363927c51a6fe9c18
+#HOMEBREW_PRODUCT=Homebrew
+#HOMEBREW_UPDATE_AFTER_HOMEBREW_HOMEBREW_DUPES=25fa9b53f943de00fc83c5a85fa0d29180eb1030
+#HOME=/Users/doug
+#HOMEBREW_UPDATE_BEFORE_HOMEBREW_HOMEBREW_DUPES=25fa9b53f943de00fc83c5a85fa0d29180eb1030
+#HOMEBREW_PREFIX=/usr/local
+#HOMEBREW_VERSION=>1.1.0 (no git repository)
+#HOMEBREW_CELLAR=/usr/local/Cellar
+#HOMEBREW_CURL=/usr/local/opt/curl/bin/curl
+#HOMEBREW_UPDATE_PREINSTALL=1
+#HOMEBREW_NO_UPDATE_CLEANUP=1
+#HOMEBREW_UPDATE_AFTER=f7bccee2145547d21b2629cab8b5fddff3299bda
+#HOMEBREW_SYSTEM=Macintosh
+
+# from an original of:
+
+#HOMEBREW_LIBRARY=/usr/local/Homebrew/Library
+#TERM=xterm-color
+#HOMEBREW_REPOSITORY=/usr/local/Homebrew
+#PATH=/usr/bin:/bin:/usr/sbin:/sbin
+#HOMEBREW_BREW_FILE=/usr/local/bin/brew
+#HOME=/Users/doug
+#HOMEBREW_PREFIX=/usr/local
+# -------------------------------------------------------------------------------------------------------------------------
+
+if [[ -n "$HOMEBREW_ENV_FILTERING" ]]
+then
+  echo "----- HOMEBREW_ENV_FILTERING set -----"
+
+  # Needed TERM to prevent "tput: No value for $TERM and no -T specified"
+  env | grep -E '^(HOMEBREW.*|HOME|PATH|TERM)=.*$' > /tmp/homebrew-env
+  env -i "$HOMEBREW_LIBRARY/Homebrew/utils/shell_env.sh" "$@"
+else
+  echo "----- HOMEBREW_ENV_FILTERING NOT set! -----"
+
+  source "$HOMEBREW_LIBRARY/Homebrew/brew.sh"
+fi