use Getopt::Long qw(GetOptions);
my $arg1;
GetOptions( 'arg1=s' => \$arg1);

##</code><code>##

use Getopt::Long qw(GetOptions);
my arg1;
my $opt = 'arg1=s => \$arg1';
my @opt = ('arg1=s', '\$arg1');
my %opt = ('arg1=s' => '\$arg1');
GetOptions($opt);   #doesn't work  
GetOptions(@opt);   #doesn't work
GetOptions(%opt);   #doesn't work