Background processes in Perl

Problem: i don't know how to set a task as a background process. My code's running on GNU/Linux, btw. I've tried adding an & before the last backticks, but it still waits for the process to end.
What it does is run the external program, so that it's output goes to a file. And i want it to run in the background.
I've tried this:
`$exe_file > $tmp_file &`;

BTW, my program is run by the user in a web browser.
I could see the perl script running by running "ps"
And i know my code works, because simple operations gives the right output.

What i plan to do is to run that binary file as an executable, and make my script check if there's already a file outputed by that binary - by refreshing the page every 5 seconds, using a meta tag (html) - and if there already is a file, it'll read the file and print it to the page.
I checked the documentation (perldoc perlfunc), but found that only "fork" is related to backgrounding - i "grepped" the documentation for "background" and only the fork part has that word.

Any help would be appreciated.

Input configuration files for EMANS

At first, the configuration files, specifically, lp_in.conf looked like this:

# shows how the input will be asked
defaults=m:2,n:2
Title=t:title
no of variables=s:n
no of constraints=s:m
Objective Function=(f:c,"x")[n]
Constraints={(f:a,"x")[n],"GLE",f:b}[m]
lower-bound=(f:lval,"x"," ")[n]
upper-bound=(f:uval,"x"," ")[n]

Cords, Fritz, Lindsay, and Adrian, however, suggested another way to write it. That is, to make it more "expandable." The above configuration just works with up to two-dimensions. This is quite ideal, since the part i'm working on is the web interface, which would only have virtually up to two-dimensional input. However, one could devise a way to allow users to input data in n-dimensions, like having them input in multiple pages, or in multiple color schemes, etc...
Now, it looks like this:

# shows how the input will be asked
defaults=m:2,n:2
Title=t:title
no of variables=s:n
no of constraints=s:m
Objective Function=(f:c,"x",$n)[n:'ADD']
Constraints=((f:a,"x",$n)[n:'ADD'],"GLE",f:b)[m]
lower-bound=(f:lval,"x",$n," ")[n]
upper-bound=(f:uval,"x",$n," ")[n]

Notice that the braces "{}" are replaced by parenthesis "()" and at the part where you'd indicate the number of elements are in an array (the one enclosed by brackets "[]"), the "joining action" done to each element in that array. For this, each element - as indicated by 'ADD' - is added to each other.