From 52f4ab315791dc639454ec593066d23e3d0ceea3 Mon Sep 17 00:00:00 2001
From: Joe Carstairs <me@joeac.net>
Date: Fri, 3 Jul 2026 12:00:02 +0100
Subject: [PATCH] more portable conditon

---
 install.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/install.sh b/install.sh
index e4be37f..2333b4a 100644
--- a/install.sh
+++ b/install.sh
@@ -87,7 +87,7 @@ do
       continue
     fi
 
-    if [ -z "${!var_name}" ]
+    if [ -z "$(expr "$(env | grep "^${var_name}=")" : "^${var_name}=\(.*\)\$")" ]
     then
       default_value="$(expr "${line}" : "^[[:alnum:]_]\+=\(.*\)\$")"
       read -sp "${var_name}: " ${var_name}