If the 1st line of your flashcount.txt file contains "5", then the following code: 
#!/usr/bin/env perl
use warnings;
use strict;

my $file = './flashcount.txt';
open my $fh, '<', $file or die "Can not open file $file: !$\n";
my $count = <$fh>;
close $fh or die "Can not close file $file: !$\n";

chomp $count;
my $outcome = $count + 1;
print "outcome = $outcome\n";

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prints (Update): 

outcome = 6

[download]

Another update: added chomp.

In reply to Re: Writing to a New File by toolic
in thread Writing to a New File by SillyMonk

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