Re: Creating a persistent state for File::Monitor

[tobyink]

Here's an example module for saved state between script runs. Save it as STATE.pm in one of your Perl library directories...

{
    package STATE;
    use strict;
    use warnings;
    use Storable qw( retrieve store );
    use constant FILENAME => sprintf '%s.state', $0;
    sub import {
        no strict 'refs';
        my $p = caller;
        *{"$p\::STATE"} = (${^STATE}{$p}||={});
    }
    sub BEGIN {
        %{^STATE} = %{ -f FILENAME ? retrieve FILENAME : {} }
    }
    sub END {
        store \%{^STATE} => FILENAME;
    }
}
1;

Now you can load that module with use STATE. Once loaded, there will be a global hash called %{^STATE} which all modules have access to. Also, within any packages that call use STATE there will also be a hash called %STATE which acts as an alias for %{${^STATE}{(__PACKAGE__)}}.

So you can write a script like this:

#!/usr/bin/perl
use STATE;
print $STATE{counter}++, "\n";

... and it will retain state between runs, the counter being incremented each time.

It does this in a rather simplistic way, using a state file with the same name as the script, just with ".state" tacked onto the end of the filename.

This is not necessarily how you'd want to do things in a major project (often the permissions of the directory where you keep the script would preclude you from storing the state there!) but serves as a good simple example I think.