use Getopt::Mixed;
{
    Getopt::Mixed::init('
        a b c d e
        alpha>a
        bravo>b
        charlie>c
        delta>d
        echo>e
    ');
    my $restricted = 0;
    my %go;
    while( my( $option, $value, $pretty ) = Getopt::Mixed::nextOption() ) {
        ++$restricted;
        $go{$option}++;
    }
    Getopt::Mixed::cleanup();

    sub go {
        my $stage = shift;
        return 1 unless $restricted;
        $go{$stage} ? 1 : 0;
    }
}

go('a') and stage_a();
go('b') and stage_b();
...

sub stage_a {
    ...
}

##</code><code>##

use Getopt::Mixed;
{
    Getopt::Mixed::init('
        a b c d e
        alpha>a
        bravo>b
        charlie>c
        delta>d
        echo>e
    ');

    my %go;
    while( my( $option, $value, $pretty ) = Getopt::Mixed::nextOption() ) {
        $go{$option}++;
    }
    Getopt::Mixed::cleanup();

    sub go {
        0 == scalar keys %go or defined( $go{$_[0]} )
    }
}

go('a') and stage_a();
go('b') and stage_b();
...

sub stage_a {
    ...
}