Only add group and user if they don't exist

install.sh

@@ -1,12 +1,20 @@
 #!/usr/bin/env bash
 
-echo "Add tablet group..."
-/usr/sbin/groupadd tablet
+set -eu
+
+GROUP=tablet
+
+if ! [ $(getent group "$GROUP") ]; then
+    echo "Add tablet group..."
+    /usr/sbin/groupadd tablet
+fi
 
 read -p "Enter your local username: " user
 
-echo "Add user to group..."
-usermod -a -G tablet "$user"
+if ! [ $(groupmems -g "$GROUP" -l | grep "$user" ) ]; then
+    echo "Add user to group..."
+    usermod -a -G tablet "$user"
+fi
 
 echo "Copy files..."
 cp -r tabletmode/ /usr/local/lib/python3.11/dist-packages