my $cmd = 'a_cmd';
my %options = (
  -d => '/home/users',
  -s => '/bin/sh',
  -g => 100,
);

$options{-c} = $realname if $realname;
$options{-d} = $base_homedir if $base_homedir;

my $cmd_str = join ' ', $cmd, map { "$_ $options{$_}" } keys %options;
my $output = qx/$cmd_str/;

##</code><code>##

my $cmd = 'a_cmd';
my @options = (
  -d => '/home/users',
  -s => '/bin/sh',
  -g => 100,
);
my $output = qx/$cmd @options/;

##</code><code>##

my @options = (
  -d => '/home/users', # you can add
  -s => '/bin/sh',     # add inline
  -g => 100,           # comments as well
  '-m',                # boolean switch
);

# instead of
my %options = (
  -d => '/home/users', # isn't it nice to be able
  -s => '/bin/sh',     # to put comments for esoteric
  -g => 100,           # external program swithces?
  -m => '',            # boolean switch
);