#!/usr/bin/perl  -w 
#######################################################
use strict;
use warnings;
use diagnostics;
use FileHandle;

my $fh=new FileHandle("< /var/run/mystamp.txt")
      or die "/var/run/mystamp.txt: $!";
my $stamp=<$fh>;

chomp $stamp;

undef $fh;

$stamp += 86400;

$fh=new FileHandle("> /var/run/mystamp.txt")
   or die "/var/run/mystamp.txt:$!";
printf $fh "%d\n",$stamp;

undef $fh;

exit(0);