Checking multiple mutually exclusive options in perl's getopt

How to check than only one of `-a` or `-b` or `-c` is defined? So not together `-a -b`, nor `-a -c`, nor `-b -c`, nor `-a -b -c`. Now have ``` use strict; use warnings; use Carp; use Getopt::Std; our($opt_a, $opt_b, $opt_c); getopts("abc"); croak("Options -a -b -c are mutually exclusive") if ( is_here_multiple($opt_a, $opt_c, $opt_c) ); sub is_here_multiple { my $x = 0; foreach my $arg (@_) { $x++ if (defined($arg) || $arg); } return $x > 1 ? 1 : 0; } ``` The above is working, but not very elegant. Here is the similar question already, but this is different, because checking two exclusive values is easy - but here is multiple ones.