$ pm_moose_default_params.pl
Option --colour = 
Option --shape = 
Moose colour = red
Moose shape = circle

$ pm_moose_default_params.pl --colour=blue
Option --colour = blue
Option --shape = 
Param colour = blue
Moose colour = blue
Moose shape = circle

$ pm_moose_default_params.pl --shape=square
Option --colour = 
Option --shape = square
Param shape = square
Moose colour = red
Moose shape = square

$ pm_moose_default_params.pl --colour=blue --shape=square
Option --colour = blue
Option --shape = square
Param colour = blue
Param shape = square
Moose colour = blue
Moose shape = square