#!/usr/bin/perl -w
use strict;

use FileHandle;
use Fcntl qw(O_RDWR O_APPEND SEEK_SET);

$| = 1;
my $flag = 1;
my $cntr = 0;
my $cntrF = shift @ARGV;

my $CF = new FileHandle $cntrF, O_RDWR | O_APPEND or die "'$cntrF' did not open: $!\n";
print $CF "$flag\n";

seek $CF, 0, SEEK_SET;

while (<$CF>) {
    while (m/\b$flag\b/g) {
        $cntr++;
    }
}
print "cntr = $cntr\n";

##</code><code>##

$ echo 1 1 1 > foo.dat
$ ./923297.pl foo.dat
cntr = 4