#!/usr/bin/perl
# 529755.pl

use strict;
use diagnostics;

my $importantdatatomangle = 1;

sub checkfornew {
	my $newversionfilename	= '529755.pl.newversion';
	if (
		-e $newversionfilename	# does the new file exist?
		and
		(time - (stat $newversionfilename)[9] > 2)
		# is it older than 2 sec, i.e. has it been completely
		# transferred to this here box?
	) {
		# save the current state of the program out to harddisk
		# i.e. $importantdatatomangle
	# ...
		warn "found a new version, running updater";
		exec 'perl updater.pl' or die "could not exec updater: $!";
		# run the updater
		# see perldoc -f exec why I included error checking
	};
};

# main program starts below here
while (1) { # loop for "many hours", actually forever :p
	{
		# do important work
		$importantdatatomangle	= -$importantdatatomangle;
		warn "data is now $importantdatatomangle";
		sleep 5;
		warn "zzzzz";
	};
	checkfornew;	# periodically check for newer version
};