#!/usr/bin/perl
use warnings;
use strict;

sub add_one_day {
    my $timestamp_file = 'timestamp.txt';

    open my $read_fh, '<', $timestamp_file;
    chomp ( my $timestamp = <$read_fh> );
    close $read_fh;

    $timestamp += 86400;

    open my $write_fh, '>', $timestamp_file;
    print   $write_fh "$timestamp\n";
    close   $write_fh;
}
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incrementing the previous timestamp by 86400, and have the crond handle it daily, but am not real sure how to go about it. I guess I need to keep track of the last timestamp in a file or something..

Here is one way of doing it. There are many:

#!/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);
[download]

That is an oversimplified IMHO way of doing it and let me outline some of the issues with this method:

• No file locking. If another instance of this script starts up then they both will attempt to update the file.
• No checking of the data in the file for validity

What you didn't say in your post is why you are doing this in the first place. In your script that uses epoch time stamps why not use time system call to generate your epoch stamp?

perl -i -pe 's/(\d+)/$1 + 86400/e' timestamp.txt
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perl -le "print+unpack'N',pack'B32','00000000000000000000001010000001'"