EXPORT

NAME

SG::Cfg - Perl extension to provide a config repository.

SYNOPSIS

        use SG::Cfg;

        my %cfg;
        tie %cfg, 'SG::Cfg';

        $cfg{hostname} = sub {
                print "Enter the hostname: ";
                my $hn = <STDIN>;
                chomp $hn;
                return $hn;
        };

        print "The hostname is $cfg{hostname}\n";

DESCRIPTION

Cfg is a reimplementation of the very flexibile config system used by Unattended (unattended.sourceforge.net). The idea is that it manages a tied hash of config variables. This appears as a normal hash to your program, but actually has some code behind the scenes.

You can either initialise the hash values with normal variables:

        $cfg{proxy} = "proxy.domain.com";

or they can be initialised with a perl function (sub) that calculates the variable value.

        $cfg{hostname} = sub {
                print "Enter the hostname: ";
                my $hn = <STDIN>;
                chomp $hn;
                return $hn;
        };

Whether a variable holds a sub or a value, you access it the same way.

        print $cfg{hostname};

The sub is only called the first time the variable is accessed. When it returns, the return value replaces it in the hash. So it is returned directly the next time.

So however many times you access the variable, the sub is only ever called once.

The sub doesn't have to ask the user for the value, it can calculate or retrieve it however it wants.

        use SG::Cfg;

        tie %cfg, 'SG::Cfg';

        $cfg{hostname} = sub {
                print "Enter the hostname: ";
                my $hn = <STDIN>;
                chomp $hn;
                return $hn;
        };

        $cfg{domain} = sub {
                print "Enter the domain: ";
                my $hn = <STDIN>;
                chomp $hn;
                return $hn;
        };

        $cfg{fqdn} = sub {
                return $cfg{hostname} . "." . $cfg{domain};
        };

        my $fqdn = $cfg{fqdn};

        print "The fully qualified domain name is: $fqdn\n";

When this is run you will see:

        Enter the hostname: www
        Enter the domain: microsoft.com
        The fully qualifified domain name is www.microsoft.com.

As the sub is only run once, this is no good for items which change over time. As Cfg operates as a cache, it will always return the same value.

EXPORT

None by default.

AUTHOR

Darryl Luff, darryl@snakegully.nu.

COPYRIGHT AND LICENSE