From 00ba2caaa683f7ca74d4b5d715c7dc02107b1c57 Mon Sep 17 00:00:00 2001
From: Filip Matzner <floop@floop.cz>
Date: Mon, 7 Aug 2017 23:48:15 +0200
Subject: [PATCH] Fix expr statement with unset $SHELL variable

In the official Ubuntu image from dockerhub, the SHELL variable
is unset. This commit makes the installation script handle it.
---
 tools/install.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/install.sh b/tools/install.sh
index 5c1a0a2ef..d7dcb069e 100755
--- a/tools/install.sh
+++ b/tools/install.sh
@@ -101,7 +101,7 @@ main() {
   mv -f ~/.zshrc-omztemp ~/.zshrc
 
   # If this user's login shell is not already "zsh", attempt to switch.
-  TEST_CURRENT_SHELL=$(expr "$SHELL" : '.*/\(.*\)')
+  TEST_CURRENT_SHELL=$(expr "${SHELL:=/bin/false}" : '.*/\(.*\)')
   if [ "$TEST_CURRENT_SHELL" != "zsh" ]; then
     # If this platform provides a "chsh" command (not Cygwin), do it, man!
     if hash chsh >/dev/null 2>&1; then