If I have a file with two numbers, say: numbers.txt:

2+3
[download]

I want to create a program which will output the sum of those numbers in a different file called sum: sum.txt:

5
[download]

Here is what I have so far: sum.pl

#!/usr/bin/perl -w
use warnings 'all';
use strict;

my $filename = 'numbers.txt';
open(N, '<', $filename);
chomp (my $numbers = <N>);
my $sum = eval $numbers;

my $outfile = "sum.txt";
open FILE, '>'.$outfile;
print FILE $sum;
close FILE;
[download]

Use of uninitialized value $sum in print at sum.pl line 17, <N> line 1.

The file could actually have more than two numbers, the program just needs to read the string expression in the file, and output the sum to another file. Thanks for help.