BEGIN {
    if (-f '/opt/location1/configuration.pm') {
        ## production environment:
        unshift( @INC,
            '/opt/location1/lib',
            '/opt/location1/scripts'
        );
    }
    else {        
        ## dev environment:
        unshift( @INC, 
            '/opt/location2/lib',
            '/opt/location2/scripts',
            '/opt/location3/debug_lib'
        );
    }
}