use Getopt::Long (); 

our $opt_float;

Getopt::Long::Configure('no_auto_abbrev','pass_through');
Getopt::Long::GetOptions('float=f')
   or die("Bad args\n");

print("\$opt_float = ", defined($opt_float) ? $opt_float : "[undef]", "\n");
print("\@ARGV      = ", join(' ', @ARGV), "\n");

##</code><code>##

>perl 551380.pl -float 1.3
$opt_float = 1.3
@ARGV      =

>perl 551380.pl -float abc
$opt_float = [undef]
@ARGV      = -float abc