use strict;
use Getopt::Long;
my $fst_a_opt_value;
my $fst_b_opt_value;

print "ARGV before = @ARGV\n";

Getopt::Long::Configure("pass_through","require_order");
GetOptions(  'a=i' => \$fst_a_opt_value,
             'b'   => \$fst_b_opt_value,
          );
          
print "first  a = $fst_a_opt_value \n";
print "first  b = $fst_b_opt_value \n";
print "ARGV after = @ARGV\n";
#
#prints 
#   ARGV before = -a 1 -b b.pl -a 2 -b 2 -c 1
#   first  a = 1
#   first  b = 1
#   ARGV after = b.pl -a 2 -b 2 -c 1