Problem matching new terminal window ID with xdotool in Bash

I have a script that kicks off a new terminal window that I want to move to a specific position on the left terminal using xdotool.

After kicking off the terminal I run

xdotool search --class gnome-term

and I use the returned Window ID in the xdotool windowsize and windowmove commands to size and position the new terminal window.

xdotool windowsize $WIN_ID 1978 407
xdotool windowmove &WIN_ID -26 702

Since I have multiple terminals running I need to identify which WIN_ID is associated with the last terminal window just created.

In the script I execute the below command before launching the new terminal to get a list of existing WIN_IDs.

for i in `xdotool search --class gnome-term`; do id_list="$id_list $i"; done

Sample content of $id_list:

65011713 65011722 65103242 65019818 65029314 65027106

After launcing the new terminal, to identify the new WIN_ID, I run this test.

for WID in `xdotool search --class gnome-term`; do if [[ ! $WID =~  $id_list ]]; then echo "New Window ID = $WID"; fi; done

When I run this command, instead of getting just one (the new) Window ID, I get all the Window IDs associated with the gnome-terminal class. Why is the below command not returning only the WID that isn’t in id_list?

if [[ ! $WID =~  $id_list ]]; then ...

Script:

...
...
# Generate a list of Window IDs for existing gnome-terminal windows
for i in `xdotool search --class gnome-term`; do id_list="$id_list $i"; done

# Kick off a new terminal window
gnome-terminal

# Get the Window ID of the new terminal window
New_WID=`for WID in `xdotool search --class gnome-term`; do if [[ ! $WID =~  $id_list ]]; then echo $WID"; fi; done`
...
...

Thanks for time and feedback!

Tex