use WarnUsedOnce;

    my $var1 = 1;
    my $var2 = 1;
    my @array;

    $var2 = 1; # $var2 used twice

    # Turn the warnings off for the following code
    no WarnUsedOnce;

    my $var3 = 2;

    __END__
    Warnings:

    Name "main::array" used only once: possible typo at test.pl line 5.
    Name "main::var1" used only once: possible typo at test.pl line 3.