diff --git a/Library/Homebrew/cmd/update.sh b/Library/Homebrew/cmd/update.sh
index a7c384a5af..19ece3f2d0 100644
--- a/Library/Homebrew/cmd/update.sh
+++ b/Library/Homebrew/cmd/update.sh
@@ -599,7 +599,6 @@ EOS
         -d "$HOMEBREW_LIBRARY/LinkedKegs" ||
         (-n "$HOMEBREW_DEVELOPER" && -z "$HOMEBREW_UPDATE_PREINSTALL") ]]
   then
-    unset HOMEBREW_RUBY_PATH
     brew update-report "$@"
     return $?
   elif [[ -z "$HOMEBREW_UPDATE_PREINSTALL" ]]
diff --git a/Library/Homebrew/utils/ruby.sh b/Library/Homebrew/utils/ruby.sh
index bd36c4d7d7..1792359767 100644
--- a/Library/Homebrew/utils/ruby.sh
+++ b/Library/Homebrew/utils/ruby.sh
@@ -1,82 +1,93 @@
+test-ruby () {
+  [[ ! -x $1 ]] && { echo "false"; return 1; }
+  "$1" --enable-frozen-string-literal --disable=gems,did_you_mean,rubyopt -rrubygems -e \
+    "puts Gem::Version.new(RUBY_VERSION.to_s.dup).to_s.split('.').first(2) == \
+          Gem::Version.new('$required_ruby_version').to_s.split('.').first(2)" 2>/dev/null
+}
+
 setup-ruby-path() {
   local vendor_dir
-  local vendor_ruby_current_version
   local vendor_ruby_path
+  local vendor_ruby_latest_version
+  local vendor_ruby_current_version
   local usable_ruby_version
   # When bumping check if HOMEBREW_MACOS_SYSTEM_RUBY_NEW_ENOUGH (in brew.sh)
   # also needs to be changed.
   local required_ruby_version="2.6"
-
-  vendor_dir="$HOMEBREW_LIBRARY/Homebrew/vendor"
-  vendor_ruby_current_version="$vendor_dir/portable-ruby/current"
-  vendor_ruby_path="$vendor_ruby_current_version/bin/ruby"
-
-  if [[ -z "$HOMEBREW_DEVELOPER" ]]
-  then
-    unset HOMEBREW_RUBY_PATH
-  fi
-
-  if [[ -z "$HOMEBREW_RUBY_PATH" && "$HOMEBREW_COMMAND" != "vendor-install" ]]
-  then
-    if [[ -x "$vendor_ruby_path" ]]
-    then
-      HOMEBREW_RUBY_PATH="$vendor_ruby_path"
-
-      if [[ $(readlink "$vendor_ruby_current_version") != "$(<"$vendor_dir/portable-ruby-version")" ]]
-      then
-        if ! brew vendor-install ruby
-        then
-          if [[ -n "$HOMEBREW_MACOS" ]]
-          then
-            odie "Failed to upgrade Homebrew Portable Ruby!"
-          else
-            odie <<-EOS
-Failed to upgrade Homebrew Portable Ruby!
+  local ruby_exec
+  local advice="
 If there's no Homebrew Portable Ruby available for your processor:
 - install Ruby $required_ruby_version with your system package manager (or rbenv/ruby-build)
 - make it first in your PATH
 - try again
-EOS
-          fi
-        fi
-      fi
-    else
-      if [[ -n "$HOMEBREW_MACOS" ]]
-      then
-        HOMEBREW_RUBY_PATH="/System/Library/Frameworks/Ruby.framework/Versions/Current/usr/bin/ruby"
-      else
-        HOMEBREW_RUBY_PATH="$(type -P ruby)"
-      fi
+"
 
-      if [[ -n "$HOMEBREW_MACOS_SYSTEM_RUBY_NEW_ENOUGH" ]]
-      then
-        usable_ruby_version="true"
-      elif [[ -n "$HOMEBREW_RUBY_PATH" && -z "$HOMEBREW_FORCE_VENDOR_RUBY" ]]
-      then
-        usable_ruby_version="$("$HOMEBREW_RUBY_PATH" --enable-frozen-string-literal --disable=gems,did_you_mean,rubyopt -rrubygems -e "puts Gem::Version.new(RUBY_VERSION.to_s.dup).to_s.split('.').first(2) == Gem::Version.new('$required_ruby_version').to_s.split('.').first(2)")"
-      fi
+  vendor_dir="$HOMEBREW_LIBRARY/Homebrew/vendor"
+  vendor_ruby_path="$vendor_dir/portable-ruby/current/bin/ruby"
+  vendor_ruby_latest_version=$(<"$vendor_dir/portable-ruby-version")
+  vendor_ruby_current_version=$(readlink "$vendor_dir/portable-ruby/current")
 
-      if [[ -z "$HOMEBREW_RUBY_PATH" || -n "$HOMEBREW_FORCE_VENDOR_RUBY" || "$usable_ruby_version" != "true" ]]
+  unset HOMEBREW_RUBY_PATH
+
+  if [[ "$HOMEBREW_COMMAND" == "vendor-install" ]]
+  then
+    return 0
+  fi
+
+  if [[ -x "$vendor_ruby_path" ]]
+  then
+    HOMEBREW_RUBY_PATH="$vendor_ruby_path"
+    if [[ $vendor_ruby_current_version != $vendor_ruby_latest_version ]]
+    then
+      if ! brew vendor-install ruby
       then
-        brew vendor-install ruby
-        if [[ ! -x "$vendor_ruby_path" ]]
+        if [[ -n "$HOMEBREW_MACOS" ]]
         then
-          if [[ -n "$HOMEBREW_MACOS" ]]
-          then
-            odie "Failed to install Homebrew Portable Ruby (and your system version is too old)!"
-          else
-            odie <<-EOS
-Failed to install Homebrew Portable Ruby and cannot find another Ruby $required_ruby_version!
-If there's no Homebrew Portable Ruby available for your processor:
-- install $required_ruby_version with your system package manager (or rbenv/ruby-build)
-- make it first in your PATH
-- try again
-EOS
-          fi
+          odie "Failed to upgrade Homebrew Portable Ruby!"
+        else
+          odie "Failed to upgrade Homebrew Portable Ruby!$advice"
         fi
-        HOMEBREW_RUBY_PATH="$vendor_ruby_path"
       fi
     fi
+  else
+    if [[ -n "$HOMEBREW_MACOS" ]]
+    then
+      HOMEBREW_RUBY_PATH="/System/Library/Frameworks/Ruby.framework/Versions/Current/usr/bin/ruby"
+    else
+      IFS=$'\n' # Do word splitting on new lines only
+      for ruby_exec in $(which -a ruby) $(PATH=$HOMEBREW_PATH which -a ruby)
+      do
+        if [[ $(test-ruby "$ruby_exec") == "true" ]]; then
+          HOMEBREW_RUBY_PATH=$ruby_exec
+          break
+        fi
+      done
+      IFS=$' \t\n' # Restore IFS to its default value
+      [[ -z $HOMEBREW_RUBY_PATH ]] && onoe "Failed to find usable Ruby $required_ruby_version!"
+    fi
+
+    if [[ -n "$HOMEBREW_MACOS_SYSTEM_RUBY_NEW_ENOUGH" ]]
+    then
+      usable_ruby_version="true"
+    elif [[ -n "$HOMEBREW_RUBY_PATH" && -z "$HOMEBREW_FORCE_VENDOR_RUBY" ]]
+    then
+      usable_ruby_version=$(test-ruby "$HOMEBREW_RUBY_PATH")
+    fi
+
+    if [[ -z "$HOMEBREW_RUBY_PATH" || -n "$HOMEBREW_FORCE_VENDOR_RUBY" || "$usable_ruby_version" != "true" ]]
+    then
+      brew vendor-install ruby
+      if [[ ! -x "$vendor_ruby_path" ]]
+      then
+        if [[ -n "$HOMEBREW_MACOS" ]]
+        then
+          odie "Failed to install Homebrew Portable Ruby (and your system version is too old)!"
+        else
+          odie "Failed to install Homebrew Portable Ruby and cannot find another Ruby $required_ruby_version!$advice"
+        fi
+      fi
+      HOMEBREW_RUBY_PATH="$vendor_ruby_path"
+    fi
   fi
 
   export HOMEBREW_RUBY_PATH