Because you updated it in a subshell. In fact it is updated - but only in the subshell and with leaving the subshell the value is lost too.

These two are identical and they:

Code:

( command )

(
    command
)

tell the shell to open a new shell and execute everything within the braces in this new shell and then close it.

The next problem is:

Code:

tot_files=$(<...>) &

This is not working at several levels.

First: what do you want to assign to the variable tot_files? Obviously the stdout of whatever is inside the subshell ( "$(...) ). It is like this:

Code:

var=$( echo "blabla" )

The shell opens a subshell and executes echo "blabla" in this subshell. So you get some output at <stdout>, in this case a string. This output is then assigned to the variable.

The next thing is you put that assignment into background:

Code:

tot_files=<something> &

But an assignment is not a separate process, it is done within the shell internally. x=5 does not generate a process you could put into background (which is in fact just another way of saying it runs asynchronously to the main process). I am not sure about that (perhaps Don Cragun knows more about these fringe situations) but i suppose that the "&" is simply ignored in this case.

The next problem is:

Code:

tot_files=<...> & | wait ${!} | <...>

A pipeline takes the <stdout> (the "normal" output) of a process and feeds it into the input (<stdin>) of another process. The output of

Code:

var=value

is <nothing>. Try it out on the commandline. When you pour that nothing into another command, what will happen, hmm? Furthermore, the wait command does not even process any input, and neither does it have any output. So, even if there would be any output from the assignment operation it would be lost by now - for the same reasons as above. So, whatever you pipe the output of wait into, there will be nothing to process because there will be no output.

Now, after this lengthy explanation of what will not work, let us finish on some positive note:

In principle you do that the following way: first display the message for the user that he should wait, then you start the lengthy process. Finally you update (or maybe redraw, depending on which possibilities are offered by your environment) the screen with a finishing message and the result of the operation:

Code:

echo "Starting calculations, hold on...."
result=<...lengthy calculation here...>
echo "Finished. Result is: $result"

As an addendum i suggest to go over the counting command itself too (to me that looks not ideal, whatever it is supposed to do), but since i do not know exactly what you want to achieve i will not suggest an alternative yet. You are welcome to post your goals and we can do that too.

I hope this helps.

bakunin