my $before;
my $arg_index = 0;
while ($arg_index < $#ARGV) {
    my $arg = $ARGV[$arg_index];
    if( $arg =~ /^-B(\d+)$/ ) {  # months Before
        $before = $1;
    } elsif( $arg =~ /^-B$/ ) {
        $before = $ARGV[++$arg_index];
        if( $before !~ /^\d+/ ) {
            die "Bad before argument ($before)\n";
        }
    }
} continue {
    ++$arg_index;
}