installer: allow chsh to work in termux

tools/install.sh

@@ -165,6 +165,13 @@ setup_shell() {
 		*) echo "Invalid choice. Shell change skipped."; return ;;
 	esac
 
+	# Check if we're running on Termux
+	case "$PREFIX" in
+		*com.termux*) termux=true; zsh=zsh ;;
+		*) termux=false ;;
+	esac
+
+	if [ "$termux" != true ]; then
 		# Test for the right location of the "shells" file
 		if [ -f /etc/shells ]; then
 			shells_file=/etc/shells
@@ -185,9 +192,10 @@ setup_shell() {
 				return
 			fi
 		fi
+	fi
 
 	# We're going to change the default shell, so back up the current one
-	if [ -n $SHELL ]; then
+	if [ -n "$SHELL" ]; then
 		echo $SHELL > ~/.shell.pre-oh-my-zsh
 	else
 		grep "^$USER:" /etc/passwd | awk -F: '{print $7}' > ~/.shell.pre-oh-my-zsh