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my $cmd = 'a_cmd';
my %options = (
...

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

my $cmd = 'a_cmd';
my @options = (
...
  -g => 100,
);
my $output = qx/$cmd @options/;

my @options = (
  -d => '/home/users', # you can add
...
  -g => 100,           # external program swithces?
  -m => '',            # boolean switch
);