Not used this before myself, no idea whether there is an established pattern. Here is my proposal:

use strict;
use warnings;
use Getopt::Long;

my %parms = (
    "os|o"   =>\(my $showos   =0),
    "rel|r"  =>\(my $showrel  =0),
    "arch|a" =>\(my $showarch =0),
    "iface|i"=>\(my $showiface=0),
    "hd|h"   =>\(my $showhd   =0),
    "mem|m"  =>\(my $showmem  =0),
    "user|u" =>\(my $showuser =0),
);

GetOptions (
    %parms,
    "all|A"  => sub { $$_=1 for values %parms },
    "help|h" => sub { &help; exit 0; }
    );

$showos=5;
print "$showos,$showrel,$showarch,$showiface,$showhd,$showmem,$showuse
+r\n";
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