make ADB_DEVICE environment variable optional

README.md

@@ -25,7 +25,9 @@ Steps:
 1. Build <br> 
     ```docker build  -t magiskupdate .```
 2. Run <br>
-    ```docker run --env ADB_DEVICE=<PUT YOUR ADB ADDR HERE> magiskupdate```
+    ```docker run --env ADB_DEVICE=<PUT YOUR ADB ADDR HERE> magiskupdate``` \
+    or, if you're lazy do: 
+    ```docker run magiskupdate```
 
 
 ## Bash

reinstall-magisk-on-lineageos

@@ -3,6 +3,9 @@
 set -e
 
 PHONE_ADB_SERIAL_NUMBER=${ADB_DEVICE} # The adb serial number can be found by running `adb devices`.
+if [$PHONE_ADB_SERIAL_NUMBER = '']; then
+    PHONE_ADB_SERIAL_NUMBER=$(echo $(adb devices) | sed -rn 's/(^|(.* ))([^ ]*) device(( .*)|$)/\3/; T; p; q')
+fi
 
 print_message() {
     printf "$1\n"