Use the Bash trap Statement to Clean Up Temporary Files

The example script works for me.

The exit commands could be quoted when calling add_on_exit but they don't have to be. The entire command line (to add_on_exit) is quoted when it is added to the array:

    on_exit_items[$n]="$*"

and the commands are added to a new element of the array:

    local n=${#on_exit_items[*]}
    on_exit_items[$n]="$*"

The syntax that you suggest for appending to the array does not preserve the existing elements.

There's not a "keyboard" trap that you can catch and beyond that since you haven't opened a terminal you don't even have a keyboard "connected" to your script. This is actually an important point: when you run a shell script from a GUI launcher, things aren't as you perhaps expect them to be. If you run ls -la /proc/$$/fd from a terminal window you'll see something like:

lrwx------ 1 user users 64 2009-07-28 09:12 0 -> /dev/pts/1
lrwx------ 1 user users 64 2009-07-28 09:12 1 -> /dev/pts/1
lrwx------ 1 user users 64 2009-07-28 09:12 2 -> /dev/pts/1

showing your stdin/stdout/stderr connected to the terminal.

If however you were to run that same command from a script launced by a GUI launcher you would see something like this:

lr-x------ 1 user users 64 2009-07-28 09:12 0 -> /dev/null
l-wx------ 1 user users 64 2009-07-28 09:12 1 -> /home/user/.xsession-errors
l-wx------ 1 user users 64 2009-07-28 09:12 2 -> /home/user/.xsession-errors

So all output ends up in your ~/.xsession-errors file and your input (stdin) is not even connected to anything useful. Note that when I said see above, I meant you'd see it in your ~/.xsession-errors file.

That said, seems to me there's a simple solution to this problem: since you don't want to open a terminal why don't you use zenity or something to ask the question in a GUI dialog box, eg:

if zenity --timeout 2 --question --text 'Connect BT mouse? '; then
    # connect mouse
    ...

or:

zenity --timeout 2 --question --text 'Connect BT mouse? '
if [ $? -eq 0 ]; then
    # connect mouse
    ...