If you want to test if something was passed, you need to test the reference that the options affects. GetOptions doesn't return anything of use.

#!/usr/bin/perl -w
use strict;
use Getopt::Long;

my $fVal = 0;

GetOptions(
           f   => \$fVal,
          )
# if "-f" is used, this will print "1" else "0"
print "$fVal\n";
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