use 5.026000;
use warnings;

use Getopt::Long;
GetOptions (
    "B|before=i" => \my $before, # An integer argument is required
    ) or die "User-friendly message\n");

##</code><code>##

GetOptions (
    "B|before:42" => \my $before, # An integer argument is optional and defaults to 42 when -B used without arg
    ) or die "User-friendly message\n");

##</code><code>##

GetOptions (
    "B|before:42" => \(my $before = 2),
    ) or die "User-friendly message\n");