You can generalize the code somewhat:

#!/usr/bin/perl
use strict;
use warnings;

my @options = qw(yes no);
my $var = 'Yes';
my $isOption = join '|', @options;

if ($var =~ /^($isOption)$/i) {
    print "Matched '$1'\n";
} else {
    print "Want one of: @options\n";
}
[download]

Prints:

Matched 'Yes'
[download]

Not that the match is now case insensitive (the /i on the regex) and it is now trivial to add new options to be matched.